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-   -   Spark knock problem (http://www.jeepforum.com/forum/f12/spark-knock-problem-1543266/)

pasinbuy 06-30-2013 05:31 PM

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?

Old4X 06-30-2013 06:06 PM

Have you checked your knock sensor?

pasinbuy 07-01-2013 11:15 AM

Never heard of it. Where is it?

Old4X 07-01-2013 12:23 PM

http://img.ptimg.com/is/image/Autos/...tos/siks168_ishttp://www.partsgeek.com/catalog/199...ck_sensor.html

Old4X 07-01-2013 12:27 PM

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.

Siva283 07-01-2013 01:03 PM

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.

pasinbuy 07-01-2013 03:50 PM

I would say carbon build up too. How do I fix it?

Would the o2 sensor have anything to do with the spark knock?

Siva283 07-01-2013 04:48 PM

Quote:

Originally Posted by pasinbuy (Post 15629442)
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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Siva283 07-01-2013 04:50 PM

Suck half the can up ahut it off for 15 mins then start it up keep the rpms up till the snoke show stop

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Old4X 07-01-2013 06:31 PM

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.

Old4X 07-01-2013 06:32 PM

Part # OMIX-ADA Part # 1722350

LJameson 07-01-2013 07:21 PM

Quote:

Originally Posted by Old4X (Post 15630105)
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

Siva283 07-01-2013 07:24 PM

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

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pasinbuy 07-02-2013 06:38 AM

Quote:

Originally Posted by Old4X (Post 15630105)
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.

pasinbuy 07-02-2013 07:46 AM

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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