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4Afe Ignition Timing/pre-Ignition Problem


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#1 maierjt

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Posted 19 September 2009 - 10:29 PM

I have a 1995 Geo Prizm Lsi, automatic, with a 1.8L 4AFE engine. Several years ago, it developed a pre-ignition knock/ping. I was told it was caused by advanced ignition timing and that, because the timing is completely controlled by the ECU, there is no way to correct the issue. Iíve confirmed the advanced timing myself with a light gun. Basic care, regular tune-ups and a new knock sensor have helped to some degree, but the pinging recently became much worse after replacing my EGR valve.



Is it true that thereís no way to adjust the ignition timing. Despite what the Chiltonís manual says, the old method of rotating the distributor doesnít seem to apply because of how the distributor is attached to the engine. Any other tips or tricks for adjusting the timing and getting rid of that annoying pre-ignition pinging?



Thanks for the help!


#2 Bitter

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Posted 19 September 2009 - 11:14 PM

i take it you lack the slot to rotate it? then its not changeable. could be a carbon buildup issue or even possible to be a bad pcm thats not controlling timing correctly. is it OBD2?

#3 maierjt

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Posted 20 September 2009 - 12:37 AM

Thanks Bitter. That's correct, there's no slot to allow the distributor to rotate. This surprised me given the fact that it is not OBDII and generally wrench-friendly without the hassles of modern computer systems.


Carbon buildup makes sense, but it sounds like the faulty PCM/ECU diagnosis might be right after all. I might clean out the air intake manifold to see if it helps, but any other insights or suggestions are much appreciated.

#4 Bitter

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Posted 20 September 2009 - 09:56 AM

well don't jump the gun on a bad computer just yet, check base timing first at idle and at 2000 rpm. then unjumper and check what its doing with timing with the knock sensor plugged in and unplugged. you can watch knock sensor voltage with a volt meter, but i have no idea whats considered normal.

as far as the carbon buildup theory, does using a higher octane fuel have any effect? like if you use 93 octane is the problem lessened? if so then it probably is a carbon issue. try a good heavy dose of seafoam through a vacuum line and let that soak over night, may need to do a couple of times. it worked wonderful on my moms mazada to cure its pinging up hills in Tennessee.

Edited by Bitter, 20 September 2009 - 09:58 AM.

#5 maierjt

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Posted 22 September 2009 - 02:32 PM

Quick update Ė Before I had the chance to dive any further into the timing, I was hit with another EGR CEL code. Iíd gotten one a few weeks prior and assumed it was the EGR valve itself after seeing that it was in poor shape. Feeling confident and/or lazy, I quickly replaced the valve and didnít bother checking the rest of the EGR system. Looks like the modulator valve was the true culprit, but I need to run a few vacuum tests and read up on part compatibility to be certain this time.

Iíll repost here if the timing issue persists after the EGR system is squared away. Thanks again for the help, though, Bitter.


#6 Bitter

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Posted 22 September 2009 - 07:31 PM

an egr issue can cause ping for sure, i forget that some years have egr since mine was without it.

#7 TRCar54

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Posted 23 September 2009 - 02:36 PM

maierjt

I got your email....sounds like you're all set. My modulator didn't cause pinging but did throw a code.

You still might want to check for carbon buildup in the intake manifold under the EGR valve though. Mine is still fine at 274K miles but it's mostly highway since I bought it and I clean it out good :D .

Good luck,
Jay in MA

Quick update – Before I had the chance to dive any further into the timing, I was hit with another EGR CEL code. I’d gotten one a few weeks prior and assumed it was the EGR valve itself after seeing that it was in poor shape. Feeling confident and/or lazy, I quickly replaced the valve and didn’t bother checking the rest of the EGR system. Looks like the modulator valve was the true culprit, but I need to run a few vacuum tests and read up on part compatibility to be certain this time.

I’ll repost here if the timing issue persists after the EGR system is squared away. Thanks again for the help, though, Bitter.


Edited by TRCar54, 23 September 2009 - 02:39 PM.