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96 Buick #4 misfire, still chasing the problem

Just found this problem, engine light on showed a misfire. Had shop double check all of the injectors and fuel pressure, all good. Install

a new fuel filter. Then did a new plugs. Thought it might be a spark plug wire, installed a know good one, no fix. Then swapped with the one next to it, still no fix. Replace coil, no fix. Replaced the ICM, no fix. Thought this could be related to the plenum problem noted here, not the issue, the engine is not using any anti-freeze. Tonight, I listened to all of the fuel injectors, all sound good.

Can a timing chain cause this kind of issue? It has never been replaced on this car and it has 165k miles on it. However, why just #4 misfire. Overall, the engine runs great at highter speeds, only misfires at idle.

Reply to
tpetaja
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I don't know about the bad injector. They did a pressure test and all looked good. Also, that is why I was listening to each injector to see if I could hear a difference. I am really wondering if I am seeing a misfire or could something else be causeing the rough idle. I am going to check the EGR out and make sure it working o.k. I had read a article that they can cause a rough idle and the computer gets faked out. What is your thought on the time chain. Too long, should it just be replaced? We commute with it, I would hate to see a major failure, but I really doubt we have a timing problem. I am just trying to get some ideas. As far as the plugs, all looked the same. Only replaced because of the misfire could and they had 110k on them. Seems like the plugs last forever now.

Thanks, Tom

Daryl Bryant wrote:

Reply to
tpetaja

Timing chain won't cause just one cylinder to misfire. Instead of randomly replacing parts, you should find the root cause.

Reply to
« Paul »

Yes, a vacuum leak can cause a rough idle that can easily be mistaken for a miss. s

Reply to
sdlomi2

"sdlomi2" wrote in news:qevCg.63$ snipped-for-privacy@newsfe04.lga:

In a feedback FI system? In my experience an air leak in a feedback FI unit results in elevated or fluctuating idle.

Reply to
TeGGeR®

Assuming compression is good, the lower intake gasket can get sucked in on GM and cause a misfire.

Reply to
Stephen H

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