Ignition knock - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 04-02-2000, 11:24 PM
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Ignition knock

My '86 with a 2.8 (255,000 mi) has developed an annoying spark rattle/knock when pulling a grade for a while, and sometimes just after shifting.

I have no error codes.

I read in another post that the MAP sensor may cause this type of problem. I did a vacuum test (mouth on longer hose), and discovered that mine does not hold a vacuum! Should it?

All other elements seem to be fine. Power is ok for a 2.8, just this annoying rattle/knock under load. I run 89 octane, unless I know I'm going to work it, then I use 92..

Thanks for the help.

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post #2 of (permalink) Old 04-03-2000, 07:27 AM
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Re: Ignition knock

Before you do anything, try this. have a certified shop do the MOTORVAC system on your truck. Check motorvac.com for information.
I had this done on my 87-s10 and it made a world of difference.

post #3 of (permalink) Old 04-07-2000, 12:20 AM
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Re: Ignition knock

The engine has had two top cleans done. Additionally, I've used two bottles of Techron (not the cheapie ProGuard stuff). I don't think that carbon build up is the problem.

Since I did the oral vacuum test, the pinging has gotten better, but it's not gone yet. Still need some help.


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