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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / August 200696 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.  SignatureBing Bang Boom Viola Done! > 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 What did the plugs look like? Did you happen to keep track of which plug came from which cylinder? The reason I ask this is because a spark plug would give indication if there was a problem at the head, perhaps is a piston issue or perhaps a injector issue! > 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. Your swapping items unnecessarily i.e. you could find yourself with more issues then the present one!! > 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. Could be a bad injector! 1st thing to do is a wet/dry compression test! This will help you determine if it's internal or something electrical! A scope will help determine if it's internal as well as a timing or electrical issue! 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 > -- > Bing Bang Boom Viola Done! [quoted text clipped - 31 lines] > A scope will help determine if it's internal as well as a timing or > electrical issue! >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. Yes, a vacuum leak can cause a rough idle that can easily be mistaken for a miss. s >>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 [quoted text clipped - 4 lines] > mistaken > for a miss. s In a feedback FI system? In my experience an air leak in a feedback FI unit results in elevated or fluctuating idle. SignatureTeGGeR® > Just found this problem, engine light on showed a misfire. Had shop > double check all of the injectors and fuel pressure, all good. Install [quoted text clipped - 11 lines] > misfire. Overall, the engine runs great at highter speeds, only > misfires at idle. Timing chain won't cause just one cylinder to misfire. Instead of randomly replacing parts, you should find the root cause. Assuming compression is good, the lower intake gasket can get sucked in on GM and cause a misfire. SignatureStephen W. Hansen ASE Certified Master Automobile Technician ASE Automobile Advanced Engine Performance ASE Undercar Specialist http://autorepair.about.com/cs/troubleshooting/l/bl_obd_main.htm http://www.troublecodes.net/technical/ http://www.familycar.com/Alignment.htm > Just found this problem, engine light on showed a misfire. Had shop > double check all of the injectors and fuel pressure, all good. Install [quoted text clipped - 11 lines] > misfire. Overall, the engine runs great at highter speeds, only > misfires at idle. |
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