4.0L Pre-Ignition Knock Advise

[dschaummann]

I have seen a great deal of good advise on this board and hope to return the favor with this information.

I have a 1994 with the 4.0 Liter engine. At around 90k miles, I started to experience pre-ignition knock at highway speeds, usually at medium to heavy throttle. My mechanic or I tried the following solutions without any help:

- Loss of EGR, replaced but not the cause
- Dirty MAF, cleaned but not the cause
- Rich mixture causing carbon buildup, cleaned carbon deposits but not the cause
- Intake bolts loose, tightened but not the cause
- Old plug wires and/or wires touching, replaced but not the cause
- Gas 87 octane, tried 89 and 93, no change
- Computer needs resetting, tried but no change
- Knock sensor, not present on this engine
- Lean fuel mix, fuel mix not the cause

I new that something had changed, because the motor didn't knock when it was new. Dealers didn't know the solution and didn't want to deal with diagnosis. Finally, my regular mechanic made the fix: replace the 10 degree advance chip with a 2 degree advance chip. When he had the meter on the timing during driving he found spark advance in the 70-80 range. The new chip counteracts the computers overzeoulous spark advance.

Now the motor doesn't knock except under extreme conditions (4th gear, 70 mph). I am happy that I have my truck back, running properyl

For those with computer issues on these engines, there is a training video which is very helpful:
Lightning Bolt Training (Automotive Videos Inc.) Mysteries of EEC IV/V (LBT-14)

 

[GenerationX]

I think I have the same problem with spark knock, especially at half to full throttle going up hills and stuff. Is that a chip in the ECM that you replaced? Is this something I could do myself or do I need some equipment to reset the computer after I do this? Thanks.

GenX

 

[Rhett]

Huh?? I'm a little dense today, I didn't understand that.

So, you're saying that the PCM has become damaged?