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Unread 07-03-2012, 11:35 PM   #1
1998daisy
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Help with jeep

I need some help. Just got a 1998 jeep Cherokee 4.0 auto. The question I have is after the jeep is warmed up it will start to misfire and act like it wants to stall. If it doesn't stall it will rev up to 2000 ramp then drop to normal idle. It has done this several times if anyone has any information I would appreciate it.

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Unread 07-04-2012, 05:53 AM   #2
n5xl
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This sounds like the behavior of a weak oxygen sensor...specifically, the "upstream" one but it could be a few other items as well. Is there a check engine light on and have you had it checked for trouble codes? Autozone and other parts houses like them often scan for troublecodes for free. If you can have them scan the codes and reply back here, I'm sure someone can offer some sound advice on the repair. If nothing else, you've got your first suggestion on the culprit.
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Unread 07-04-2012, 08:37 AM   #3
CJ7-Tim
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As suggested, it sounds like you are describing some sensor issues that occur when the the Jeep switches to closed loop operation.

Test the O2 sensors, they can get old and slow to react. Typical O2 sensor service life is about 100,000-150,000 miles.
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Unread 07-04-2012, 11:02 AM   #4
1998daisy
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I disconnected the upper o2 sensor were gonna test drive and trouble shoot it
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Unread 07-09-2012, 10:47 PM   #5
1998daisy
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I bought a new o2 sensor and put it in. I also put in sea foam into the gas tank. The jeep will still stall but only when the temp is at or above 210. I can let it idle for about 10 min and it'll start to stutter and catch itself back up it still stalls but less frequently than before. Anything else I can check out???!!!! ): I'm looking at changing the thermostat and checking the idle timing, because its idling a little too high. Help please.
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Unread 07-09-2012, 10:48 PM   #6
1998daisy
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I also went to auto zone and did code test and nothing came up ):
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Unread 07-10-2012, 06:23 PM   #7
CJ7-Tim
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Clean the Idle Air Controller. Test the TPS.



Cleaning the Idle Air Controller (IAC) :

Purchase sensor safe Throttle Body cleaner spray.


1. Remove the Throttle body from the intake manifold.
2. Remove the IAC with a TORX 15 driver (2 bolts)
3. Gently wiggle out the IAC from the throttle body
4. Clean the IAC with Throttle Body Cleaner (not carburetor cleaner). Use cleaner, a rag, and a toothbrush. Be gentle; don’t twist or pull on the pintle as it is fragile and can be damaged easily
5. Also clean where the IAC seats in the throttle body with the same throttle body cleaner

6. While you have the Throttle Body off, give it a good cleaning also.
7. Reinstall IAC, the Throttle body, and check idle quality.


.




TPS

You may have one or more of these Physical Symptoms:

1) The engine loses power and is stalling.
2) The engine will idle, but may die as soon as you press the gas pedal. When driving, it seems as if all power is gone.
3) Sometimes it feels as if the transmission is failed or isn't shifting properly, if at all. If you quickly jump on the gas you might be able to get the transmission to shift, but it won’t shift properly by itself. Shifting manually, the transmission goes through all the gears.

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics. The TPS function should be verified early in the troubleshooting process, when a transmission issue is suspected.

TPS TEST

The TPS is mounted on the throttle body. The TPS is a variable resistor that provides the Powertrain Control Module (PCM) with an input signal (voltage) that represents throttle blade position. The sensor is connected to the throttle blade shaft. As the
position of the throttle blade changes, the resistance of the TPS changes. Along with inputs from other sensors, the PCM uses the TPS input to determine current engine operating conditions. In response to engine operating conditions, the PCM will adjust fuel injector pulse width and ignition timing.

The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. The PCM receives an input signal voltage from the TPS. It is best to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts.
This will vary in an approximate range of from .25 volts at minimum throttle opening (idle), to 4.8 volts at WOT wide open throttle.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.


The TPS is sensitive to heat, moisture, and vibration, leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following:

-Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".

- High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.

-Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.

-Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted accordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.

- Engine Misfire: A faulty TPS can report values outside the acceptable range causing the ECU to incorrectly fuel the engine. This is noticeable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessive misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.


You may have one or more of these Physical Symptoms:

4) The engine loses power and is stalling.
5) The engine will idle, but may die as soon as you press the gas pedal. When driving, it seems as if all power is gone.
6) Sometimes it feels as if the transmission is failed or isn't shifting properly, if at all. If you quickly jump on the gas you might be able to get the transmission to shift, but it won’t shift properly by itself. Shifting manually, the transmission goes through all the gears.

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics. The TPS function should be verified early in the troubleshooting process, when a transmission issue is suspected.

TPS TEST

You should have 5 volts going into the Throttle Position Sensor (TPS). It is best to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. At idle, TPS output voltage should be greater than .26 volts but less than .95 volts. Move the throttle and look for smooth meter response up to the 4.49 at WOT. The other wire will be the ground and should show no voltage.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.


The TPS is sensitive to heat, moisture, and vibration, leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following:

-Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".

- High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.

-Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.

-Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted accordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.

- Engine Misfire: A faulty TPS can report values outside the acceptable range causing the ECU to incorrectly fuel the engine. This is noticeable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessive misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.
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Progressive Liberalism: Bringing you new Healthcare ideas so wonderful, they have to include mandatory participation ......

Originally Posted by Ronald W. Reagan: Government is not the solution to our problem; Government is the problem.
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Unread 07-11-2012, 10:21 PM   #8
1998daisy
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Alright I went to checkers /O'Riley's and codes came up. My temperature sensor isn't working. I bought the part but still waiting on all the wires. Another code came up as well, something may be wrong with my whole fuel pump or maybe just the sensor. I'm going to change the temp sensor first and see how that goes. I also put in a thermostat, the jeep never even had one in. But now that we put the thermostat in the bottom bolt by the gasket is leaking. Anyone have thoughts on that? But now that its installed the jeep hasn't gone over 220. (:





I will also be checking everything you told me in the last post. Thank you so much for the info. I greatly appreciate it.
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Unread 07-12-2012, 09:54 PM   #9
1998daisy
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Does anyone know the correct psi for the fuel pump? I can't find it on Google. And i don't have the manual for my jeep.
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Unread 07-13-2012, 06:25 AM   #10
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IIRC you should have 45 psi +/- at the fuel rail
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Unread 07-13-2012, 06:41 AM   #11
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Quote:
Originally Posted by 1998daisy View Post
Does anyone know the correct psi for the fuel pump? I can't find it on Google. And i don't have the manual for my jeep.
Your '98 should have 49.2 +/- 5 psi at the fuel rail.
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Unread 07-16-2012, 02:59 AM   #12
1998daisy
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I replaced my fuel pump, it was pretty horrible. I believe it was the original. It was pushing way too much fuel causing my engine to stall. No that its been replaced this is day #2 and no stalling! (: thank you so much everyone for trying to help me fix this problem! Oliver appreciate all the input! (: again thank you (:
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Unread 07-16-2012, 06:03 AM   #13
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Quote:
Originally Posted by 1998daisy View Post
I replaced my fuel pump, it was pretty horrible. I believe it was the original. It was pushing way too much fuel causing my engine to stall. No that its been replaced this is day #2 and no stalling! (: thank you so much everyone for trying to help me fix this problem! Oliver appreciate all the input! (: again thank you (:
Just curious...what do you mean 'pushing way too much fuel'? Was the pressure too high? If so, what was the pressure?
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