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Unread 02-19-2012, 03:19 AM   #31
JugaLug
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1983 CJ7 
 
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I installed my own JY TBI system. I have had the same problem. I took mine in to have it Dyno tuned, this took care of the problem of running poorly, but left me with the Jeep shutting off when I would slow down or stop. It is a problem with the IAC. Get some TB cleaner and spray it into the IAC. Carbon will build up in the IAC and give you problems faster than you think.

After talking to the Dyno Shop employees, I have learned that even the complete systems need tuning after installed. The chip supplied with the kit is a generic chip meant to work with all installs, but not all engines are the same.

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Unread 02-19-2012, 04:42 AM   #32
james04si
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The Howell kit is pretty close to tuned as compared to the junkyard TBI. They went through and tuned it pretty good for the 258. Even with a different cam and the 4.0 head on mine it was pretty close to begain with. I did however spend some time on binderplanet.com and thirdgen.org and dialed it in the rest of the way. If you have a stock motor you shouldn't have to make any changes from the Howell bin file.
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Unread 02-19-2012, 05:39 AM   #33
BioTex
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Closed or open loop, the engine should still run. Sounds exactly like a bad ignition component. Like a failing module.
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'85 CJ7, BDS 4" lift, 1" Body lift, 33x12.5, Shrockworks Sliders, 304 V8 with RV cam., T-176, D300, Dana 30, AMC 20.
1986 CJ10-A SD-33 Diesel/727/np208
1971 800B with 345/T-19
06' TJ Rubicon, 4" R.C. springs, BFG/AT 35s M.C. 6" fenders, rockers and surrounds, Currie front & rear adj. tracbars, tattons DC rear shaft, adj. upper - lower CA's. Bilstein 5100's
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Unread 02-19-2012, 05:48 AM   #34
james04si
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I agree that open loop or closed loop shouldn't make much difference. I just got carried away talking about the TBI. I do still feel there is an issue that needs to be addressed as to why the check engine light is not on while cranking after it dies.
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Unread 02-19-2012, 05:53 AM   #35
BioTex
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Quote:
Originally Posted by james04si View Post
I agree that open loop or closed loop shouldn't make much difference. I just got carried away talking about the TBI. I do still feel there is an issue that needs to be addressed as to why the check engine light is not on while cranking after it dies.
I don't believe a failing module will cause the light.
__________________
'85 CJ7, BDS 4" lift, 1" Body lift, 33x12.5, Shrockworks Sliders, 304 V8 with RV cam., T-176, D300, Dana 30, AMC 20.
1986 CJ10-A SD-33 Diesel/727/np208
1971 800B with 345/T-19
06' TJ Rubicon, 4" R.C. springs, BFG/AT 35s M.C. 6" fenders, rockers and surrounds, Currie front & rear adj. tracbars, tattons DC rear shaft, adj. upper - lower CA's. Bilstein 5100's
YJ Buggy Build Current project. Stroker/FI ?
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Unread 02-19-2012, 07:36 AM   #36
walkerhoundvm
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Quote:
Originally Posted by BioTex View Post
I don't believe a failing module will cause the light.
There's a bunch of things that won't cause a CE light to pop on, some of them within the system, some out. I think you might be on to something here, BT. If JeepHammer were here I bet he'd give a sermon on why this has every indication of a failing module.
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Unread 02-19-2012, 07:58 AM   #37
gmakra
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The ECM has a learn block mode so it will tune its self to a degree and it takes about 10-20 times for it to really learn they engine. I borrowed this from. www.thirdgen.orgmaybe this will shed some light on open and closed loop.

Modern Engine Controls: More than I can say or remember in 20 minutes

JETHROIROC Mar 31 2006 - 3:39pm I. Introduction:

1. Fundamental needs of a four-stroke IC engine – Fuel and air in the correct proportions accompanied by a reliable and properly timed spark.

2. Engine control – A means of meeting the above needs of IC engines.
· Past – Mechanical, Thermal-Fluid
· Present – Electrical, Computers

3. Motivation for computer controlled engines
· Increased fuel economy
· Environmental regulation (EPA, 1970’s)
· Optimum performance as restricted by environmental concerns
· The evolution of solid-state electronics
· Improved driveability/reliability
· System failure diagnosis/warnings of engine malfunction (generally via “Service Engine Soon” dummy light, but control problems especially easy to pinpoint by technicians equipped with diagnostic computers)

4. Engine systems that are electronically controlled/monitored
· Fuel/Air delivery system
· Ignition system
· Exhaust system


II. Greater Engine Control Subsystems:

1. Fuel/Air – This system is equipped to determine intake air mass flowrate, and subsequently control fuel metering so as to ensure a stoichiometric AF mass ratio (14.7:1) in each cylinder during closed loop operation, although there is no AF ratio that minimizes all harmful combustion byproducts simultaneously (but most are optimized at stoichiometric conditions). This system seldom allows greater than a ±1.0 deviation from stoichiometric conditions instantaneously, and the average AF ratio is maintained to within ±0.05 on most modern automobiles equipped with three-way catalytic converters.

Components of modern Fuel/Air Regulation Systems:

a. Throttle Position Sensor (TPS) – Generally uses a potentiometer device to measure the instantaneous position of the throttle plate, which is mechanically linked to the accelerator pedal. This sensor is almost always positioned on the throttle body itself. Accordingly, conditions of hard acceleration and heavy engine load or deceleration will be detected by this device and the fuel/air system will increase or decrease fuel injector pulse duration accordingly. This action is “overriding” in the sense that it allows rapid maximum engine performance in the event of an evasive maneuver as dictated by the driver, at the expense of emissions and fuel economy control. Such action is permissible by the EPA, mainly for safety considerations. Note: Throttle angle may also be used in conjunction with vehicle and engine speed to initiate idle speed control operation of the fuel/air system. A bypass (IAC) valve is generally used to permit the intake of combustion air under closed throttle conditions.

b. Mass Air Flow Sensor (MAF) – Located in the air intake duct between the filter element and the throttle body, input from this sensor regulates the amount of fuel to be metered to each cylinder in an attempt to achieve the stoichiometric ratio. A derivative of the hot-wire anemometer (a heated wire cooled by the air passing over it), using a Wheatstone bridge and a variable-resistance heated element the MAF can produce a near-linear signal from which the mass flowrate of air is easily determined by the engine control module. The greater the mass flowrate of air over the sensor, the greater the voltage required to heat the wire element. The actual airflow measurement is likely the most important variable in determining the amount of fuel to be metered to the engine. Although this device is very accurate, it tends to be somewhat delicate and expensive.

c. Manifold Absolute Pressure Sensor (MAP) – Used on all “speed-density” systems (those not measuring airflow directly), this device measures the absolute pressure of air in the intake manifold using a silicon diaphragm strain sensor and the piezoresistivity phenomenon. The output of the MAP sensor is used in conjunction with intake manifold air temperature, engine displacement, RPM, exhaust gas recirculation amount and various constants to determine the amount of incoming combustion air and consequently the amount of fuel to be metered. Closed throttle plate would represent close to a vacuum in the intake manifold, whereas wide-open throttle should be near atmospheric pressure, the maximum intake manifold pressure for a normally aspirated engine.

· Speed-density method used in MAP systems is described as follows:
Recall that the mass flowrate of air is represented by the product of the air density and its volumetric flowrate. The instantaneous density is calculated by multiplying the density of air at standard conditions by the ratios of MAP and MAT data with respect to standard atmospheric conditions for temperature and pressure. The volume flow rate of air into the engine is simply the product of engine RPM and half of the displacement (it only draws one half the total engine displacement in one revolution under ideal conditions). Figure in corrections for exhaust gas recirculation and other small factors, and the mass flowrate of air into the intake manifold at any given instant is easily determined by the onboard engine computer.
· Note: Some vehicles are equipped with both MAF and MAP systems, relying on MAF data unless a malfunction is encountered, whereupon the engine control module will default to the speed-density method.

d. Manifold Absolute Temperature Sensor (MAT) – Measures the temperature of incoming combustion air to be used in those systems performing speed-density calculations to determine airflow.

e. Fuel Injectors (FI) – Solenoid actuators that deliver atomized fuel to cylinders based upon other sensor input, mainly MAF (or airflow by speed-density method) and engine crankshaft position (CPS). The volumetric flowrate allowed by fuel injector nozzles is essentially constant and determined by the pressure of the fuel system itself. Therefore, the amount of fuel actually delivered by injectors is regulated only by the duration in which they spray fuel, called the “pulse width.”

· Throttle Body Injection (TBI) – This system delivers fuel in much the same way as a carburetor, generally above the throttle plate at the top of the intake manifold (usually right under the air filter cover plate in the center of the filter element). Actual fuel delivery, however, is accomplished by the engine control module and two or four fuel injectors. Therefore, this system is described as a “wet” system, as the fuel and air must travel through the intake runners together. Accordingly, this can cause some of the atomized fuel to settle out (condense), leading to somewhat ineffective and uneven charge delivery to the cylinders. The biggest advantage of this system is that the fuel is precisely metered each time, without the physical sensitivity of a carburetor.

· Multiport Injection (MPI) – This system locates one or two injectors directly above each intake valve, where the fuel can be delivered very precisely. A vehicle equipped with MPI is said to have a “dry” system, as only air must travel through the intake runners. High fuel pressure (about 65 psi in the system and 40 psi at the injector nozzles) is also applied to sufficiently atomize the fuel discharged by injector nozzles. As one might guess, fuel condensation is eliminated by this system, resulting in more power, better throttle response and increased fuel economy. The only drawback of this system is the increased cost and complexity of a vehicle equipped with at least one injector per cylinder. Otherwise, MPI systems are superior to both TBI and carbureted systems.

· Sequential Fuel Injection vs. Batch Fire – Although these are not physical injector configurations, the manner in which injector pulses are dictated is very important to engine performance and environmental variables as well. A sequential fuel injection system triggers one injector at a time following the firing sequence of the engine. Batch fire systems trigger multiple injectors simultaneously, sometimes grouping cylinders to receive fuel in “banks.” Due to the fact that batch fired injectors pulse more than once per cylinder cycle (usually twice), only half the fuel is delivered at a time. Essentially, the first pulse of fuel is fired with the intake valve closed, and then a second pulse is released just when the valve opens. SFI systems are more precise and optimize all engine performance characteristics, although such systems require more involved electronic controls.

Ž Sequential, multiport fuel injection (SMPI or SFI) is the most sophisticated means of fuel delivery as of now, and many newer vehicles are equipped with this system.

f. Ignition System (IGN) – Must provide an electric spark of the proper timing using intake manifold pressure data, engine RPM, crankshaft position and temperature measurements. This system is included here as it sometimes is not controlled by a separate module, simply because many of the important ignition timing calculation factors are stored/determined by the fuel/air system.

g. Oxygen Sensors (EGO) – An integral part of the system’s closed-loop feedback control once heated above 300oC, oxygen sensors most commonly utilize zirconium dioxide (ZrO2) for its tendency to attract oxygen ions and are generally located in more than one section of the exhaust system. To achieve the most accurate results, EGO sensors should be located at the first point where they will receive a multicylinder mix reading (usually in the tubing just beyond the exhaust manifold, before the catalytic converter), and some vehicles have more than one EGO sensor in different locations (exhaust manifolds, one past the catalytic converter). This device generates a voltage based upon the concentration of oxygen in engine exhaust and sensor temperature which is then used to indirectly relay the fuel/air system’s effectiveness in achieving the stoichiometric AF ratio, operating as a correction factor to the MAF data. It is also notable that heated EGO sensors are now used on many vehicles, allowing closed loop operation and thusly optimum system control to begin much sooner after startup.

h. Coolant Temperature Sensor (CTS) – Determines the temperature of engine coolant via direct insertion with a thermistor, usually threaded into a coolant passage in the intake manifold. This data is then used to determine the point at which the engine is warmed and a leaner mixture may be used by the fuel/air system in an open loop fashion prior to oxygen sensor warm-up. Coolant temperature is also used during engine cranking to set the starting AF ratio to a value between 2:1 and 12:1.

i. Crankshaft Position Sensor (CPS) – Recall that one complete engine cycle (four-stroke) requires a 720o rotation of the crankshaft. The crankshaft angular position can be measured as referenced to top dead center (TDC) for each cylinder, generally via magnetic or optical means. The camshaft may also be used as an indirect measurement of crankshaft position, as it rotates at ½ the crankshaft speed. Crankshaft position data is then used for ignition timing and fuel delivery timing, and may also be used to determine engine speed.


2. Ignition/Spark – Must provide a reliable and properly timed electric spark to each cylinder to ignite combustion reactants and promote proper flame propagation rather than detonation. Ignition of combustion reactants takes place before top dead center of the compression piston stroke. The ignition system operates most effectively at the minimum advance for best timing (MBT) decided upon by engine RPM, crankshaft position, temperature and manifold absolute pressure data. The spark advance is measured in degrees before TDC, and must vary according to the type of fuel used as well as those variables previously mentioned. When the spark is advanced too far, autoignition (detonation, “knock”) of some fraction of the fuel and air mixture may occur. Recall that autoignition is generally caused by one of two things, although there are many others; fuel of an octane rating that is too low for physical engine parameters (compression ratio), or excessive spark advance. The ignition system must maximize performance under fixed AF ratio conditions as dictated by the fuel/air system. It can either function as a separate unit, or as an integrated system within the fuel/air system.

a. Crankshaft Position – Provides the direct timing signal to the ignition system and all other sensor input is essentially an elaboration on this value. Obviously, the ignition system must know the actual engine position before any spark advance can be computed!

b. Manifold Absolute Pressure – Contributes to the overall calculation of spark advance, which is generally reduced for an increase in this variable. This value is applied to a table in read-only memory (ROM) of the engine control module to determine an appropriate advance correction factor.

c. Coolant Temperature – Used with ROM tables to obtain yet another correction factor, the determination of which is beyond discussion here.

d. Engine RPM – A correction factor based mostly on engine characteristics is obtained from pre-programmed tables in accordance with engine RPM data. As a general rule, spark advance should increase with increasing engine RPM to a certain point (2500 RPM or so) and then remain close to constant in performance engines. It is a known phenomenon that flame propagation speed can increase proportionally with engine speed, but it only does so enough to avoid advance with increasing RPM in racing/high compression engines with increased turbulence in the combustion chamber (especially above 3000 RPM, where the spark may even be retarded at high engine speeds > 5000RPM). In stock cars and trucks that most of us drive (low compression, less combustion chamber turbulence), flame propagation increases much more slowly than does RPM and therefore further spark advance is essential up to around 5000RPM, by either a centrifugal and/or vacuum advance mechanism or electronic control. Although fast (about 1 millisecond), a spark still requires a finite amount of time in which to take place, and an increase in RPM shrinks this “window.” The exception to this is under idle conditions, where the spark must be advanced as well to compensate for longer combustion time under low manifold pressure conditions. At any rate, ignition science literally varies from car to car, and fuel to fuel. There is no exact method for all cars, or an exact method for any one car…only a “best timing” for a given set of conditions.

e. Knock Sensor – This device senses the presence of “knock,” or excessive cylinder pressure via magnetostriction, piezoresistivity or piezoelectric crystal accelerometers. The knock sensor is generally threaded into the cylinder block itself to sense vibration. Accordingly, the ignition is retarded when a knock is sensed and until the point at which knocking ceases. Essentially, the addition of this sensor can provide for closed-loop operation of the ignition system.

Ž You may have noticed that spark advance decreases with increasing manifold absolute pressure, but increases with increasing RPM. Ironically, manifold absolute pressure increases with increasing RPM, and this is the reason for their separate correction factors and combined use. Spark timing is still debatable and far from an exact science, and generally the spark advance at a given instant is simply a compromise between many factors that conflict one another but are summed to provide a decent result.


3. Exhaust/Exhaust Gas Recirculation – A system designed to evacuate the cylinders of spent combustion products and protect the environment from harmful byproducts, including nitric oxides (NOx), fuel remnants (HC) and carbon monoxide (CO), while redirecting a portion of exhaust gases back into cylinders for mixing with fresh environmental air and fuel. Recirculation can greatly minimize the expulsion of NOx to the environment by lowering peak combustion temperature.

a. Oxidizing Catalyst – Use permits a reduction in harmful combustion product emission via an increased reaction rate, thereby allowing better engine performance calibration under strict environmental regulations. May require the incorporation of additional environmental air to operate effectively; the effectiveness of this device is also directly related to temperature.
· Oxidizes hydrocarbons to CO2 and H2O
· Oxidizes CO to CO2
· Reduces NOx to diatomic nitrogen and oxygen

b. Three-Way Catalyst (TWC) – Found in most modern systems, the TWC uses a mixture of platinum, palladium and rhodium to reduce all three major harmful emissions concurrently. The efficiency of this device is largely affected by AF, with stoichiometric conditions being the optimum working range. Although fluctuations from 14.7:1 for a finite duration are tolerable, the average AF ratio must be very near stoichiometric. This device is only effective when used in conjunction with a modern fuel/air control system and unleaded fuel, whereupon it is capable of reducing pollutants by up to 90%.

c. Exhaust Gas Recirculation Valve (EGR) – Recirculates a controlled amount of exhaust gases back into the intake, lowering combustion temperature and resulting in a profound decrease in NOx even in the event that only small amounts of exhaust gas are reconsumed. Generally uses a solenoid or vacuum actuated valve that is precisely controlled by the engine computer via an exhaust and intake manifold differential pressure sensor (DPS) to provide EGR as a function of engine load. However, a decrease in performance and an increase in fuel consumption are undesirable side effects of this device and process.


III. Putting Things Together – The Modes of Operation:

1. Closed loop vs. Open Loop Control – While operating in an open loop fashion, the onboard computer functions without the input of exhaust gas oxygen sensors, and therefore will use only MAF or MAP and RPM to determine the correct amount of fuel and EGR to be metered, and the proper spark advance. When the EGO sensor warms sufficiently, closed loop control is initiated wherein a correction factor based upon EGO output is applied to the fuel injector pulse duration calculation as made in open loop operation. This is where the fine-tuning takes place.

2. Start Mode – The only concern at this point is quick and reliable engine start.

· RPM is set to cranking speed
· Engine coolant is at environmental temperature
· Low AF ratio (2:1 to 12:1)
· Spark timing retarded
· No exhaust gas recirculation
· Fuel economy and emissions not under optimum control

3. Warm-up Mode – The main concern at this point is a clean and fast transition from engine start to normal operating conditions.

· RPM may be adjusted by the driver almost instantly
· Engine coolant temperature rises to minimum operating value (before opening of the thermostat)
· Low AF ratio (12:1 to 14:1)
· Spark timing adjusted by ignition control system
· No exhaust gas recirculation
· Fuel economy and emissions not under optimum control

4. Open Loop Mode – Fuel economy and emissions controlled and of concern, without the aid of EGO sensors.

· RPM readily adjusted by driver
· Engine coolant is warmed to operating temperature
· AF ratio roughly controlled to 14.7:1
· EGR is used
· Spark timing adjusted by ignition control system
· Fuel economy and emissions controlled without help of EGO sensors

5. Closed Loop Mode – Fuel economy and emissions controlled to the closest extent possible.

· RPM controlled by driver
· Engine coolant at operating temperature
· AF ratio controlled closely at 14.7:1 ± 0.05
· EGO sensor warmed sufficiently to enter the control loop
· System resumes open loop operation if EGO fails to operate properly
· EGR system in operation
· Fuel and emissions strictly controlled

6. Hard Acceleration Mode (WOT) – Maximum performance and safety of concern in this mode, with fuel economy and emissions of little consideration.

· Throttle plate wide open as dictated by driver
· Engine coolant temperature in normal range
· AF ratio rich (13:1)
· EGR and EGO are not used at all
· Poor fuel economy and emissions control

7. Deceleration and Idle Mode – Fuel economy and emissions of primary concern, as is preventing engine stall.

· RPM dropping quickly or constant at idle speed
· Engine coolant at normal operating temperature
· AF ratio lean
· Idle mode engaged to minimize RPM fluctuations in the event that accessories are used by the driver (air conditioning, etc.)
· Emissions sometimes drastically reduced with deceleration
· EGR is in operation
· Poor fuel economy at idle, but good fuel economy with deceleration

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Unread 02-19-2012, 08:01 AM   #38
gmakra
Registered User
1985 CJ7 
 
Join Date: Jun 2008
Location: Chicago area
Posts: 2,746
The ECM has a learn block mode so it will tune its self to a degree and it takes about 10-20 times for it to really learn they engine. I borrowed this from. www.thirdgen.orgmaybe this will shed some light on open and closed loop.

Modern Engine Controls: More than I can say or remember in 20 minutes

JETHROIROC Mar 31 2006 - 3:39pm I. Introduction:

1. Fundamental needs of a four-stroke IC engine – Fuel and air in the correct proportions accompanied by a reliable and properly timed spark.

2. Engine control – A means of meeting the above needs of IC engines.
· Past – Mechanical, Thermal-Fluid
· Present – Electrical, Computers

3. Motivation for computer controlled engines
· Increased fuel economy
· Environmental regulation (EPA, 1970’s)
· Optimum performance as restricted by environmental concerns
· The evolution of solid-state electronics
· Improved driveability/reliability
· System failure diagnosis/warnings of engine malfunction (generally via “Service Engine Soon” dummy light, but control problems especially easy to pinpoint by technicians equipped with diagnostic computers)

4. Engine systems that are electronically controlled/monitored
· Fuel/Air delivery system
· Ignition system
· Exhaust system


II. Greater Engine Control Subsystems:

1. Fuel/Air – This system is equipped to determine intake air mass flowrate, and subsequently control fuel metering so as to ensure a stoichiometric AF mass ratio (14.7:1) in each cylinder during closed loop operation, although there is no AF ratio that minimizes all harmful combustion byproducts simultaneously (but most are optimized at stoichiometric conditions). This system seldom allows greater than a ±1.0 deviation from stoichiometric conditions instantaneously, and the average AF ratio is maintained to within ±0.05 on most modern automobiles equipped with three-way catalytic converters.

Components of modern Fuel/Air Regulation Systems:

a. Throttle Position Sensor (TPS) – Generally uses a potentiometer device to measure the instantaneous position of the throttle plate, which is mechanically linked to the accelerator pedal. This sensor is almost always positioned on the throttle body itself. Accordingly, conditions of hard acceleration and heavy engine load or deceleration will be detected by this device and the fuel/air system will increase or decrease fuel injector pulse duration accordingly. This action is “overriding” in the sense that it allows rapid maximum engine performance in the event of an evasive maneuver as dictated by the driver, at the expense of emissions and fuel economy control. Such action is permissible by the EPA, mainly for safety considerations. Note: Throttle angle may also be used in conjunction with vehicle and engine speed to initiate idle speed control operation of the fuel/air system. A bypass (IAC) valve is generally used to permit the intake of combustion air under closed throttle conditions.

b. Mass Air Flow Sensor (MAF) – Located in the air intake duct between the filter element and the throttle body, input from this sensor regulates the amount of fuel to be metered to each cylinder in an attempt to achieve the stoichiometric ratio. A derivative of the hot-wire anemometer (a heated wire cooled by the air passing over it), using a Wheatstone bridge and a variable-resistance heated element the MAF can produce a near-linear signal from which the mass flowrate of air is easily determined by the engine control module. The greater the mass flowrate of air over the sensor, the greater the voltage required to heat the wire element. The actual airflow measurement is likely the most important variable in determining the amount of fuel to be metered to the engine. Although this device is very accurate, it tends to be somewhat delicate and expensive.

c. Manifold Absolute Pressure Sensor (MAP) – Used on all “speed-density” systems (those not measuring airflow directly), this device measures the absolute pressure of air in the intake manifold using a silicon diaphragm strain sensor and the piezoresistivity phenomenon. The output of the MAP sensor is used in conjunction with intake manifold air temperature, engine displacement, RPM, exhaust gas recirculation amount and various constants to determine the amount of incoming combustion air and consequently the amount of fuel to be metered. Closed throttle plate would represent close to a vacuum in the intake manifold, whereas wide-open throttle should be near atmospheric pressure, the maximum intake manifold pressure for a normally aspirated engine.

· Speed-density method used in MAP systems is described as follows:
Recall that the mass flowrate of air is represented by the product of the air density and its volumetric flowrate. The instantaneous density is calculated by multiplying the density of air at standard conditions by the ratios of MAP and MAT data with respect to standard atmospheric conditions for temperature and pressure. The volume flow rate of air into the engine is simply the product of engine RPM and half of the displacement (it only draws one half the total engine displacement in one revolution under ideal conditions). Figure in corrections for exhaust gas recirculation and other small factors, and the mass flowrate of air into the intake manifold at any given instant is easily determined by the onboard engine computer.
· Note: Some vehicles are equipped with both MAF and MAP systems, relying on MAF data unless a malfunction is encountered, whereupon the engine control module will default to the speed-density method.

d. Manifold Absolute Temperature Sensor (MAT) – Measures the temperature of incoming combustion air to be used in those systems performing speed-density calculations to determine airflow.

e. Fuel Injectors (FI) – Solenoid actuators that deliver atomized fuel to cylinders based upon other sensor input, mainly MAF (or airflow by speed-density method) and engine crankshaft position (CPS). The volumetric flowrate allowed by fuel injector nozzles is essentially constant and determined by the pressure of the fuel system itself. Therefore, the amount of fuel actually delivered by injectors is regulated only by the duration in which they spray fuel, called the “pulse width.”

· Throttle Body Injection (TBI) – This system delivers fuel in much the same way as a carburetor, generally above the throttle plate at the top of the intake manifold (usually right under the air filter cover plate in the center of the filter element). Actual fuel delivery, however, is accomplished by the engine control module and two or four fuel injectors. Therefore, this system is described as a “wet” system, as the fuel and air must travel through the intake runners together. Accordingly, this can cause some of the atomized fuel to settle out (condense), leading to somewhat ineffective and uneven charge delivery to the cylinders. The biggest advantage of this system is that the fuel is precisely metered each time, without the physical sensitivity of a carburetor.

· Multiport Injection (MPI) – This system locates one or two injectors directly above each intake valve, where the fuel can be delivered very precisely. A vehicle equipped with MPI is said to have a “dry” system, as only air must travel through the intake runners. High fuel pressure (about 65 psi in the system and 40 psi at the injector nozzles) is also applied to sufficiently atomize the fuel discharged by injector nozzles. As one might guess, fuel condensation is eliminated by this system, resulting in more power, better throttle response and increased fuel economy. The only drawback of this system is the increased cost and complexity of a vehicle equipped with at least one injector per cylinder. Otherwise, MPI systems are superior to both TBI and carbureted systems.

· Sequential Fuel Injection vs. Batch Fire – Although these are not physical injector configurations, the manner in which injector pulses are dictated is very important to engine performance and environmental variables as well. A sequential fuel injection system triggers one injector at a time following the firing sequence of the engine. Batch fire systems trigger multiple injectors simultaneously, sometimes grouping cylinders to receive fuel in “banks.” Due to the fact that batch fired injectors pulse more than once per cylinder cycle (usually twice), only half the fuel is delivered at a time. Essentially, the first pulse of fuel is fired with the intake valve closed, and then a second pulse is released just when the valve opens. SFI systems are more precise and optimize all engine performance characteristics, although such systems require more involved electronic controls.

Ž Sequential, multiport fuel injection (SMPI or SFI) is the most sophisticated means of fuel delivery as of now, and many newer vehicles are equipped with this system.

f. Ignition System (IGN) – Must provide an electric spark of the proper timing using intake manifold pressure data, engine RPM, crankshaft position and temperature measurements. This system is included here as it sometimes is not controlled by a separate module, simply because many of the important ignition timing calculation factors are stored/determined by the fuel/air system.

g. Oxygen Sensors (EGO) – An integral part of the system’s closed-loop feedback control once heated above 300oC, oxygen sensors most commonly utilize zirconium dioxide (ZrO2) for its tendency to attract oxygen ions and are generally located in more than one section of the exhaust system. To achieve the most accurate results, EGO sensors should be located at the first point where they will receive a multicylinder mix reading (usually in the tubing just beyond the exhaust manifold, before the catalytic converter), and some vehicles have more than one EGO sensor in different locations (exhaust manifolds, one past the catalytic converter). This device generates a voltage based upon the concentration of oxygen in engine exhaust and sensor temperature which is then used to indirectly relay the fuel/air system’s effectiveness in achieving the stoichiometric AF ratio, operating as a correction factor to the MAF data. It is also notable that heated EGO sensors are now used on many vehicles, allowing closed loop operation and thusly optimum system control to begin much sooner after startup.

h. Coolant Temperature Sensor (CTS) – Determines the temperature of engine coolant via direct insertion with a thermistor, usually threaded into a coolant passage in the intake manifold. This data is then used to determine the point at which the engine is warmed and a leaner mixture may be used by the fuel/air system in an open loop fashion prior to oxygen sensor warm-up. Coolant temperature is also used during engine cranking to set the starting AF ratio to a value between 2:1 and 12:1.

i. Crankshaft Position Sensor (CPS) – Recall that one complete engine cycle (four-stroke) requires a 720o rotation of the crankshaft. The crankshaft angular position can be measured as referenced to top dead center (TDC) for each cylinder, generally via magnetic or optical means. The camshaft may also be used as an indirect measurement of crankshaft position, as it rotates at ½ the crankshaft speed. Crankshaft position data is then used for ignition timing and fuel delivery timing, and may also be used to determine engine speed.


2. Ignition/Spark – Must provide a reliable and properly timed electric spark to each cylinder to ignite combustion reactants and promote proper flame propagation rather than detonation. Ignition of combustion reactants takes place before top dead center of the compression piston stroke. The ignition system operates most effectively at the minimum advance for best timing (MBT) decided upon by engine RPM, crankshaft position, temperature and manifold absolute pressure data. The spark advance is measured in degrees before TDC, and must vary according to the type of fuel used as well as those variables previously mentioned. When the spark is advanced too far, autoignition (detonation, “knock”) of some fraction of the fuel and air mixture may occur. Recall that autoignition is generally caused by one of two things, although there are many others; fuel of an octane rating that is too low for physical engine parameters (compression ratio), or excessive spark advance. The ignition system must maximize performance under fixed AF ratio conditions as dictated by the fuel/air system. It can either function as a separate unit, or as an integrated system within the fuel/air system.

a. Crankshaft Position – Provides the direct timing signal to the ignition system and all other sensor input is essentially an elaboration on this value. Obviously, the ignition system must know the actual engine position before any spark advance can be computed!

b. Manifold Absolute Pressure – Contributes to the overall calculation of spark advance, which is generally reduced for an increase in this variable. This value is applied to a table in read-only memory (ROM) of the engine control module to determine an appropriate advance correction factor.

c. Coolant Temperature – Used with ROM tables to obtain yet another correction factor, the determination of which is beyond discussion here.

d. Engine RPM – A correction factor based mostly on engine characteristics is obtained from pre-programmed tables in accordance with engine RPM data. As a general rule, spark advance should increase with increasing engine RPM to a certain point (2500 RPM or so) and then remain close to constant in performance engines. It is a known phenomenon that flame propagation speed can increase proportionally with engine speed, but it only does so enough to avoid advance with increasing RPM in racing/high compression engines with increased turbulence in the combustion chamber (especially above 3000 RPM, where the spark may even be retarded at high engine speeds > 5000RPM). In stock cars and trucks that most of us drive (low compression, less combustion chamber turbulence), flame propagation increases much more slowly than does RPM and therefore further spark advance is essential up to around 5000RPM, by either a centrifugal and/or vacuum advance mechanism or electronic control. Although fast (about 1 millisecond), a spark still requires a finite amount of time in which to take place, and an increase in RPM shrinks this “window.” The exception to this is under idle conditions, where the spark must be advanced as well to compensate for longer combustion time under low manifold pressure conditions. At any rate, ignition science literally varies from car to car, and fuel to fuel. There is no exact method for all cars, or an exact method for any one car…only a “best timing” for a given set of conditions.

e. Knock Sensor – This device senses the presence of “knock,” or excessive cylinder pressure via magnetostriction, piezoresistivity or piezoelectric crystal accelerometers. The knock sensor is generally threaded into the cylinder block itself to sense vibration. Accordingly, the ignition is retarded when a knock is sensed and until the point at which knocking ceases. Essentially, the addition of this sensor can provide for closed-loop operation of the ignition system.

Ž You may have noticed that spark advance decreases with increasing manifold absolute pressure, but increases with increasing RPM. Ironically, manifold absolute pressure increases with increasing RPM, and this is the reason for their separate correction factors and combined use. Spark timing is still debatable and far from an exact science, and generally the spark advance at a given instant is simply a compromise between many factors that conflict one another but are summed to provide a decent result.


3. Exhaust/Exhaust Gas Recirculation – A system designed to evacuate the cylinders of spent combustion products and protect the environment from harmful byproducts, including nitric oxides (NOx), fuel remnants (HC) and carbon monoxide (CO), while redirecting a portion of exhaust gases back into cylinders for mixing with fresh environmental air and fuel. Recirculation can greatly minimize the expulsion of NOx to the environment by lowering peak combustion temperature.

a. Oxidizing Catalyst – Use permits a reduction in harmful combustion product emission via an increased reaction rate, thereby allowing better engine performance calibration under strict environmental regulations. May require the incorporation of additional environmental air to operate effectively; the effectiveness of this device is also directly related to temperature.
· Oxidizes hydrocarbons to CO2 and H2O
· Oxidizes CO to CO2
· Reduces NOx to diatomic nitrogen and oxygen

b. Three-Way Catalyst (TWC) – Found in most modern systems, the TWC uses a mixture of platinum, palladium and rhodium to reduce all three major harmful emissions concurrently. The efficiency of this device is largely affected by AF, with stoichiometric conditions being the optimum working range. Although fluctuations from 14.7:1 for a finite duration are tolerable, the average AF ratio must be very near stoichiometric. This device is only effective when used in conjunction with a modern fuel/air control system and unleaded fuel, whereupon it is capable of reducing pollutants by up to 90%.

c. Exhaust Gas Recirculation Valve (EGR) – Recirculates a controlled amount of exhaust gases back into the intake, lowering combustion temperature and resulting in a profound decrease in NOx even in the event that only small amounts of exhaust gas are reconsumed. Generally uses a solenoid or vacuum actuated valve that is precisely controlled by the engine computer via an exhaust and intake manifold differential pressure sensor (DPS) to provide EGR as a function of engine load. However, a decrease in performance and an increase in fuel consumption are undesirable side effects of this device and process.


III. Putting Things Together – The Modes of Operation:

1. Closed loop vs. Open Loop Control – While operating in an open loop fashion, the onboard computer functions without the input of exhaust gas oxygen sensors, and therefore will use only MAF or MAP and RPM to determine the correct amount of fuel and EGR to be metered, and the proper spark advance. When the EGO sensor warms sufficiently, closed loop control is initiated wherein a correction factor based upon EGO output is applied to the fuel injector pulse duration calculation as made in open loop operation. This is where the fine-tuning takes place.

2. Start Mode – The only concern at this point is quick and reliable engine start.

· RPM is set to cranking speed
· Engine coolant is at environmental temperature
· Low AF ratio (2:1 to 12:1)
· Spark timing retarded
· No exhaust gas recirculation
· Fuel economy and emissions not under optimum control

3. Warm-up Mode – The main concern at this point is a clean and fast transition from engine start to normal operating conditions.

· RPM may be adjusted by the driver almost instantly
· Engine coolant temperature rises to minimum operating value (before opening of the thermostat)
· Low AF ratio (12:1 to 14:1)
· Spark timing adjusted by ignition control system
· No exhaust gas recirculation
· Fuel economy and emissions not under optimum control

4. Open Loop Mode – Fuel economy and emissions controlled and of concern, without the aid of EGO sensors.

· RPM readily adjusted by driver
· Engine coolant is warmed to operating temperature
· AF ratio roughly controlled to 14.7:1
· EGR is used
· Spark timing adjusted by ignition control system
· Fuel economy and emissions controlled without help of EGO sensors

5. Closed Loop Mode – Fuel economy and emissions controlled to the closest extent possible.

· RPM controlled by driver
· Engine coolant at operating temperature
· AF ratio controlled closely at 14.7:1 ± 0.05
· EGO sensor warmed sufficiently to enter the control loop
· System resumes open loop operation if EGO fails to operate properly
· EGR system in operation
· Fuel and emissions strictly controlled

6. Hard Acceleration Mode (WOT) – Maximum performance and safety of concern in this mode, with fuel economy and emissions of little consideration.

· Throttle plate wide open as dictated by driver
· Engine coolant temperature in normal range
· AF ratio rich (13:1)
· EGR and EGO are not used at all
· Poor fuel economy and emissions control

7. Deceleration and Idle Mode – Fuel economy and emissions of primary concern, as is preventing engine stall.

· RPM dropping quickly or constant at idle speed
· Engine coolant at normal operating temperature
· AF ratio lean
· Idle mode engaged to minimize RPM fluctuations in the event that accessories are used by the driver (air conditioning, etc.)
· Emissions sometimes drastically reduced with deceleration
· EGR is in operation
· Poor fuel economy at idle, but good fuel economy with deceleration

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Unread 02-27-2012, 12:58 PM   #39
outdoorguy86
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So a bit of an update, I havent had a ton of time to work on the jeep lately, but I did manage to get it running well enough to get me to work twice last week

So what I ended up doing was pulling out the IAC and cleaning the plug and the surrounding housing. I also unscreweed any grounds I could find and took the wire brush to them. I havent gotten around to buying some connectors and heavy gauge wire to do dedicated grounds yet. I drilled out the idle adjustment plug and upped the idle a little bit, it now sits closer to 700 when warmed up now. The RPMs still drop a bit when you let off the gas to cruise (could this be because I dont have the EGR hooked up??). I also adjusted the TPS accordingly after messing with the idle.

Drove it on saturday to go hiking, had it die on me several times, but thats because I ran out of gas....

So a little summary of what the issue was and what I did that seemed to have solved the issue (for now) for future reference:

Problem: Jeep would start fine and drive fine when cold. When it got warmed up it would stall when coming to a stop or cruising. RPMs would drop low and it would just stall.

What I did to try and fix it: Team rush, new coil, new ICM, new temp sensor, new MAP, new O2 sensor, cleaning off grounds, soaking fuel injectors in carb cleaner, cleaning IAC, adjusting TPS, increasing idle.

Big thanks to all those who contributed suggestions and experiences.
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Unread 02-27-2012, 05:11 PM   #40
dslywalker
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Thanx for the update.Not related but had that same issue with my Dodge truck.Cleaned the IAC and TPS and it went away. Another problem i had with my Howell was low voltage at idle actually no voltage as the battery was failing and altenator wasn't putting out to much at idle.It would stutter a little and die.
One more problem i had[hope i ain't boring you] is the starter solenoid was shorting out intermitantly and keeping the fuel pump running flooding everything out.I've had Howell for about 14 years now and its never been a Howell problem just the things that make it operate.
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Unread 03-02-2012, 11:14 AM   #41
outdoorguy86
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Well the problem is not 100% solved. It is still stalling out, but not nearly as often. Drove it twice this week and it did it twice. The first time, I dont think I let the engine warm up quite enough. Second time I was on the Hwy doing probably 60. I've figured out how to get it back on the road pretty quickly though. Just unplugg both injectors, start it up to burn what fuel is in there, then plug them back in and it will start right back up. Still leaning a little towards bad ground, and the right bump messes something up. Driving it down to Colorado Springs this weekend to store in my old mans garage and start some major work (look for a build thread in the future). Anyone want to get in on the pool of how many times it is going to stall out on the way down there...
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Unread 03-02-2012, 11:38 AM   #42
walkerhoundvm
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So it sounds almost convincingly like a fuel delivery issue, with you being able to "fix" it by burning the fuel off?

I think she's doing what she's supposed to, but something in the mix isn't giving the computer the right signal or, as I mentioned earlier, you may have a return flow obstruction. Have you unplugged the return line and blown through it to see that it's not partially blocked? You should be able to blow through it and hear it back from the tank.

Otherwise, let's hear a little more about your sensors. Where is your coolant sensor - manifold or block? And how about your O2 sensor - do you have headers (single or dual) or the original exhaust manifold? Where is the sensor in there? And your MAP sensor is higher than your throttle body, right? As far as you can tell that hose that feeds it is unobstructed?

And my guess is you'll conk out three times. Once at 36 and I-25, the next at Speer and I-25, and once around Larkspur, far enough from anything that you'll be worried you can't get her started up again.
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Unread 03-02-2012, 12:09 PM   #43
outdoorguy86
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Quote:
Originally Posted by walkerhoundvm View Post
So it sounds almost convincingly like a fuel delivery issue, with you being able to "fix" it by burning the fuel off?

I think she's doing what she's supposed to, but something in the mix isn't giving the computer the right signal or, as I mentioned earlier, you may have a return flow obstruction. Have you unplugged the return line and blown through it to see that it's not partially blocked? You should be able to blow through it and hear it back from the tank.

Otherwise, let's hear a little more about your sensors. Where is your coolant sensor - manifold or block? And how about your O2 sensor - do you have headers (single or dual) or the original exhaust manifold? Where is the sensor in there? And your MAP sensor is higher than your throttle body, right? As far as you can tell that hose that feeds it is unobstructed?

And my guess is you'll conk out three times. Once at 36 and I-25, the next at Speer and I-25, and once around Larkspur, far enough from anything that you'll be worried you can't get her started up again.

I've got a short section or rubber hose that connects down tot he metal tubing that goes back to the tank. I know that the rubber section is clear. I have not blown through the metal tubing. I was going under the assumption that there was not a blockage in the return by the fact that my pressure in was looking ok.

Coolant sensor is mounted on the manifold. O2 sensor is located right below the flange on the exhaust tube. Map sensor is up above the TBI with less than 12" of hose.

I agree that the computer is not getting a proper signal from something, which is why I'm still leaning towards grounding. I think the cleaning I did helped, but dedicated grounds are obviously going to be a big improvement.
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Unread 03-02-2012, 05:46 PM   #44
dslywalker
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I always found this site informative.Should be 3 links to open on the page or more.Even thou its for a Motor Home principle is the same.Hope you make it
http://www.bdub.net/jrwheeler/
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Unread 03-04-2012, 08:55 PM   #45
outdoorguy86
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Who had her quitting 3 times.... Ran a lot further than I expected before having issues. Made it all the way down to Palmer Park before she quit out. Got her going again, then about 5 miles later it happened again, then 3 miles after that. Let her sit for a little while and that got me all the way home to Black Forest.

Spent all weekend getting my other truck back together (older tahoe) after some damage due to a accident coming back from skiing.

After sitting for a day, tried to start her up this afternoon and one of the injectors was sticking wide open and flooding the engine out. Got it running well enough to move on just one injector.

I cant remember off of the top of my head, but do the injectors open or close when they get grounded? In other words, would a bad ground cause it to possibly stick open. I'd like to continue to think this is an electrical/grounding issue before I start spending $80 on a fuel injector.....

dslywalker, thanks for the link. It looks like its got some good stuff I'll have to read through.
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