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Unread 06-30-2013, 05:31 PM   #1
pasinbuy
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1994 YJ Wrangler 
 
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Spark knock problem

I have a 94 6cyl and been having a spark knock problem for a while.

Yes premium gas does get rid of it. But at another $8.00 a tank I would rather fix the problem.

Full tune up about 11 months ago, plug, wires, cap, rotor, and new coil.

When the spark knock starts I can run the rpm's up to around 3000 for a few miles to clean her out and get rid of the spark knock, but the spark knock returns a couple hundred miles later.

Other than that runs strong. Any suggestion?

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Unread 06-30-2013, 06:06 PM   #2
Old4X
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Have you checked your knock sensor?
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Unread 07-01-2013, 11:15 AM   #3
pasinbuy
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Never heard of it. Where is it?
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Unread 07-01-2013, 12:23 PM   #4
Old4X
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Unread 07-01-2013, 12:27 PM   #5
Old4X
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Looks like the above pic with a 2 wire harness plugged in. Not sure on the FI engines, the 4.2 has one on the intake.
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Unread 07-01-2013, 01:03 PM   #6
Siva283
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Pretty sure the fuel injected engines do not have those. I have yet to find one on mine anyway. Have you checked compression. Could be carbon build up in the cylinders. If premium gas gets rid of it I would bet on high compression numbers.
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1995 YJ. 2 inch BDS Spring lift. 1 inch shackle lift. 1.25 inch JKS Body Lift 33x12.5x15's. Engo 10,000 pound winch.

[QUOTE=Magnum;14117863] I gave the Jeep the required offering of $$, sweat, and blood, and everything works fine now. -- Jim[/QUOTE]

[QUOTE=ldso;16498409]. It started with a $200 axle, and a few thousand dollars later I was done :)[/QUOTE]

[QUOTE=Luuca;16122017]diagnose the real issue before you start going all Obama on it - spending mad cash you'll need for other important things.

Ask me how I know...[/QUOTE]

[QUOTE=Overhead;17658665]this is also my second set of RC springs this year. I'd rather spend the money again and get something that will last.[/QUOTE]
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Unread 07-01-2013, 03:50 PM   #7
pasinbuy
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I would say carbon build up too. How do I fix it?

Would the o2 sensor have anything to do with the spark knock?
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Unread 07-01-2013, 04:48 PM   #8
Siva283
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Quote:
Originally Posted by pasinbuy View Post
I would say carbon build up too. How do I fix it?

Would the o2 sensor have anything to do with the spark knock?
Seafoam through the brake vooster hose. Its amazing stuff

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__________________
1995 YJ. 2 inch BDS Spring lift. 1 inch shackle lift. 1.25 inch JKS Body Lift 33x12.5x15's. Engo 10,000 pound winch.

[QUOTE=Magnum;14117863] I gave the Jeep the required offering of $$, sweat, and blood, and everything works fine now. -- Jim[/QUOTE]

[QUOTE=ldso;16498409]. It started with a $200 axle, and a few thousand dollars later I was done :)[/QUOTE]

[QUOTE=Luuca;16122017]diagnose the real issue before you start going all Obama on it - spending mad cash you'll need for other important things.

Ask me how I know...[/QUOTE]

[QUOTE=Overhead;17658665]this is also my second set of RC springs this year. I'd rather spend the money again and get something that will last.[/QUOTE]
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Unread 07-01-2013, 04:50 PM   #9
Siva283
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Suck half the can up ahut it off for 15 mins then start it up keep the rpms up till the snoke show stop

Sent from my SPH-L300 using JeepForum
__________________
1995 YJ. 2 inch BDS Spring lift. 1 inch shackle lift. 1.25 inch JKS Body Lift 33x12.5x15's. Engo 10,000 pound winch.

[QUOTE=Magnum;14117863] I gave the Jeep the required offering of $$, sweat, and blood, and everything works fine now. -- Jim[/QUOTE]

[QUOTE=ldso;16498409]. It started with a $200 axle, and a few thousand dollars later I was done :)[/QUOTE]

[QUOTE=Luuca;16122017]diagnose the real issue before you start going all Obama on it - spending mad cash you'll need for other important things.

Ask me how I know...[/QUOTE]

[QUOTE=Overhead;17658665]this is also my second set of RC springs this year. I'd rather spend the money again and get something that will last.[/QUOTE]
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Unread 07-01-2013, 06:31 PM   #10
Old4X
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The 94 4.0 does have a knock sensor. If bad or disconnected, the engine WILL knock.

Pull out your factory manual and test it. Do not waste your money on snake oil.
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Unread 07-01-2013, 06:32 PM   #11
Old4X
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Part # OMIX-ADA Part # 1722350
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Unread 07-01-2013, 07:21 PM   #12
LJameson
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Quote:
Originally Posted by Old4X View Post
The 94 4.0 does have a knock sensor. If bad or disconnected, the engine WILL knock.
Not according to the FSM...

Quote:
PCM SYSTEM
The computerized engine control system is built around a Powertrain Control Module (PCM) . The PCM monitors up to 22 inputs and responds with appropriate outputs to manage fuel delivery, ignition timing, and emission control devices, charging system, speed control and idle speed.

NOTE: The PCM can detect certain faults in its systems, the following is a list of the types of faults the PCM can detect.

MONITORED CIRCUITS
Open or Shorted Circuit - The PCM can determine if the input signal from the sensor is within its range and if the sensor circuit is open or shorted.

Output Device Current Flow - The PCM can see if the output devices are hooked up. If a problem exists with an output devices' circuit, the PCM can determine if it is open, shorted high, or shorted to ground.

Oxygen Sensor - Once the system has entered closed loop, the PCM checks that the oxygen sensor is switching between rich and lean.

PCM INPUTS


•A/C Request
•A/C Select
•ASD Sense
•Battery Voltage
•Brake Switch
•Camshaft Position Sensor
•Crankshaft Position Sensor
•Data Link Receive
•Engine Coolant Temp Sensor
•Generator Output
•Ignition Circuit Sense
•Intake Air Temp Sensor
•MAP Sensor
•Overdrive/Override Switch
•Oxygen Sensor
•Park/Neutral Switch
•Power Ground
•Speed Control Set Switch
•Signal Ground
•Speed Control Resume Switch
•Throttle Position Sensor
•Vehicle Speed Sensor
PCM OUTPUTS


•A/C clutch
•Generator Field
•ASD Relay
•Data Link Transmit
•Electronic EGR Transducer
•EVAP Purge Solenoid
•Fuel Injectors
•Fuel Pump Relay
•Ignition Coil
•Idle Air Control Motor
•Malfunction Indicator Lamp
•Shift Indicator Lamp
•Speed Control Solenoids
•Tachometer

NOTE: Not all models use all inputs and outputs.
The only 4.0's I've seen with Knock Sensors are the RENIX 4.0's.

Quote:
Starting in 1991, the Jeep 4.0 engine used Chrysler engine computers, allowing for easier diagnostics; before that, Crysler had to honor contracts with AMC's ignition system vendor, Renix. There are two yellow rubber covers on the right side of the engine compartment; dealers can use the DRBII and the Jeep adapter to get codes and do certain tests. (Codes might not be stored in the Renix system and would have to be regenerated while the adapter was connected, according to Rob Mayercik.) Frank Swygert wrote that the 1991 system works in a similar manner, but uses a different type of CPS, no knock sensor or EGR, and complies with OBD requirements.
http://www.allpar.com/mopar/40.html
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Unread 07-01-2013, 07:24 PM   #13
Siva283
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Join Date: May 2011
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Seafoam does an amazing job. When I replaced the old engine with 260,000 miles and when I tore it down it was pristine inside except for the broken valve that took oit the number 2 pistion. Def not snake oil

Sent from my SPH-L300 using JeepForum
__________________
1995 YJ. 2 inch BDS Spring lift. 1 inch shackle lift. 1.25 inch JKS Body Lift 33x12.5x15's. Engo 10,000 pound winch.

[QUOTE=Magnum;14117863] I gave the Jeep the required offering of $$, sweat, and blood, and everything works fine now. -- Jim[/QUOTE]

[QUOTE=ldso;16498409]. It started with a $200 axle, and a few thousand dollars later I was done :)[/QUOTE]

[QUOTE=Luuca;16122017]diagnose the real issue before you start going all Obama on it - spending mad cash you'll need for other important things.

Ask me how I know...[/QUOTE]

[QUOTE=Overhead;17658665]this is also my second set of RC springs this year. I'd rather spend the money again and get something that will last.[/QUOTE]
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Unread 07-02-2013, 06:38 AM   #14
pasinbuy
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Location: florida
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Quote:
Originally Posted by Old4X View Post
The 94 4.0 does have a knock sensor. If bad or disconnected, the engine WILL knock.

Pull out your factory manual and test it. Do not waste your money on snake oil.
I see your part number. Do you know where it is located on the motor?


I have used Seafoam. It did not cure my problem, only a short mask.
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Unread 07-02-2013, 07:46 AM   #15
pasinbuy
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Okay, I looked and there is no knock sensor. I also did a search and even though a part is listed, no knock sensor.

Any suggestions on how to fix the spark knock? Plugs are rc12lyc. New wires, coil, cap, and rotor.
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