Random misfire woes
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Random misfire woes
Hey all,
My 2000 Civic SI has been experiencing random misfires for a while now and I finally tracked down the cause. Since this seems to be a common problem with Civics in general, I thought I'd share my experience and my solution.
When I first got a flashing CEL, I assumed that it was an ignition issue, and since the car had nearly 200K miles on it , I decided that it was due for some new ignition parts. I put in new NGK plugs, plug wires, distributor cap and rotor. The misfires disappeared as expected, but only for a couple of weeks.
When they came back, I took a look at the fuel side. Fuel delivery was normal and the filter was clean. Because of the high mileage, I decided that it might be time for new injectors, and changed them out. The misfire problem again disappeared, but then returned in a couple of weeks.
Then I began the fun task of looking for an intermittent electrical connection. After much trial and error, I found that if I wiggled the wiring harness passing under the intake manifold, I could recreate the misfire at idle. Since there was a tech note about fraying insulation on that harness I figured that must be the problem. To avoid the major trouble and expense of replacing the entire engine wiring harness, I opted to bypass the part of the harness in question and rewire the injectors myself directly to the ECM. That again cured the misfire problem, but only temporarily.
When the random misfire beast AGAIN returned, I seriously considered torching the whole thing and moving on to another vehicle. Instead, I revisited my search for the electrical gremlin and finally found a bad fuel injector plug on the number one cylinder. Apparently the contacts in the plug had worn from years of engine vibration and it was making intermittent contact with the fuel injector. After a search for new plugs proved fruitless, I cut a small piece of brass shim, folded it in two and inserted it into the plug. When the plug was put back on the injector, the shim made contact between the plug and injector contacts and cured the problem. I have since found new plugs with pigtails that I can splice into the wiring harness, but the temporary fix has been working fine for several months. The only casualty of the whole process, besides my patience, was the cat which succumbed to all of the various misfire events.
Apparently, whenever I would work on the engine, the injector plugs were jostled enough that the engine ran fine for a while, but then the contact eventually became intermittent again. Hopefully this will help others cure this simple but perplexing problem if they are experiencing random misfires on a higher mileage Civic.
Tom
My 2000 Civic SI has been experiencing random misfires for a while now and I finally tracked down the cause. Since this seems to be a common problem with Civics in general, I thought I'd share my experience and my solution.
When I first got a flashing CEL, I assumed that it was an ignition issue, and since the car had nearly 200K miles on it , I decided that it was due for some new ignition parts. I put in new NGK plugs, plug wires, distributor cap and rotor. The misfires disappeared as expected, but only for a couple of weeks.
When they came back, I took a look at the fuel side. Fuel delivery was normal and the filter was clean. Because of the high mileage, I decided that it might be time for new injectors, and changed them out. The misfire problem again disappeared, but then returned in a couple of weeks.
Then I began the fun task of looking for an intermittent electrical connection. After much trial and error, I found that if I wiggled the wiring harness passing under the intake manifold, I could recreate the misfire at idle. Since there was a tech note about fraying insulation on that harness I figured that must be the problem. To avoid the major trouble and expense of replacing the entire engine wiring harness, I opted to bypass the part of the harness in question and rewire the injectors myself directly to the ECM. That again cured the misfire problem, but only temporarily.
When the random misfire beast AGAIN returned, I seriously considered torching the whole thing and moving on to another vehicle. Instead, I revisited my search for the electrical gremlin and finally found a bad fuel injector plug on the number one cylinder. Apparently the contacts in the plug had worn from years of engine vibration and it was making intermittent contact with the fuel injector. After a search for new plugs proved fruitless, I cut a small piece of brass shim, folded it in two and inserted it into the plug. When the plug was put back on the injector, the shim made contact between the plug and injector contacts and cured the problem. I have since found new plugs with pigtails that I can splice into the wiring harness, but the temporary fix has been working fine for several months. The only casualty of the whole process, besides my patience, was the cat which succumbed to all of the various misfire events.
Apparently, whenever I would work on the engine, the injector plugs were jostled enough that the engine ran fine for a while, but then the contact eventually became intermittent again. Hopefully this will help others cure this simple but perplexing problem if they are experiencing random misfires on a higher mileage Civic.
Tom
Last edited by TLGriff; Sep 9, 2011 at 11:12 AM.
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Re: Random misfire woes
Yeah man. Those Type A misfires can easily kill the cat. Thanks for posting this. Hopefully others will take the plugs into consideration because people always seem to go for the injectors themselves as the culprit.
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Hey all,
My 2000 Civic SI has been experiencing random misfires for a while now and I finally tracked down the cause. Since this seems to be a common problem with Civics in general, I thought I'd share my experience and my solution.
When I first got a flashing CEL, I assumed that it was an ignition issue, and since the car had nearly 200K miles on it , I decided that it was due for some new ignition parts. I put in new NGK plugs, plug wires, distributor cap and rotor. The misfires disappeared as expected, but only for a couple of weeks.
When they came back, I took a look at the fuel side. Fuel delivery was normal and the filter was clean. Because of the high mileage, I decided that it might be time for new injectors, and changed them out. The misfire problem again disappeared, but then returned in a couple of weeks.
Then I began the fun task of looking for an intermittent electrical connection. After much trial and error, I found that if I wiggled the wiring harness passing under the intake manifold, I could recreate the misfire at idle. Since there was a tech note about fraying insulation on that harness I figured that must be the problem. To avoid the major trouble and expense of replacing the entire engine wiring harness, I opted to bypass the part of the harness in question and rewire the injectors myself directly to the ECM. That again cured the misfire problem, but only temporarily.
When the random misfire beast AGAIN returned, I seriously considered torching the whole thing and moving on to another vehicle. Instead, I revisited my search for the electrical gremlin and finally found a bad fuel injector plug on the number one cylinder. Apparently the contacts in the plug had worn from years of engine vibration and it was making intermittent contact with the fuel injector. After a search for new plugs proved fruitless, I cut a small piece of brass shim, folded it in two and inserted it into the plug. When the plug was put back on the injector, the shim made contact between the plug and injector contacts and cured the problem. I have since found new plugs with pigtails that I can splice into the wiring harness, but the temporary fix has been working fine for several months. The only casualty of the whole process, besides my patience, was the cat which succumbed to all of the various misfire events.
Apparently, whenever I would work on the engine, the injector plugs were jostled enough that the engine ran fine for a while, but then the contact eventually became intermittent again. Hopefully this will help others cure this simple but perplexing problem if they are experiencing random misfires on a higher mileage Civic.
Tom
My 2000 Civic SI has been experiencing random misfires for a while now and I finally tracked down the cause. Since this seems to be a common problem with Civics in general, I thought I'd share my experience and my solution.
When I first got a flashing CEL, I assumed that it was an ignition issue, and since the car had nearly 200K miles on it , I decided that it was due for some new ignition parts. I put in new NGK plugs, plug wires, distributor cap and rotor. The misfires disappeared as expected, but only for a couple of weeks.
When they came back, I took a look at the fuel side. Fuel delivery was normal and the filter was clean. Because of the high mileage, I decided that it might be time for new injectors, and changed them out. The misfire problem again disappeared, but then returned in a couple of weeks.
Then I began the fun task of looking for an intermittent electrical connection. After much trial and error, I found that if I wiggled the wiring harness passing under the intake manifold, I could recreate the misfire at idle. Since there was a tech note about fraying insulation on that harness I figured that must be the problem. To avoid the major trouble and expense of replacing the entire engine wiring harness, I opted to bypass the part of the harness in question and rewire the injectors myself directly to the ECM. That again cured the misfire problem, but only temporarily.
When the random misfire beast AGAIN returned, I seriously considered torching the whole thing and moving on to another vehicle. Instead, I revisited my search for the electrical gremlin and finally found a bad fuel injector plug on the number one cylinder. Apparently the contacts in the plug had worn from years of engine vibration and it was making intermittent contact with the fuel injector. After a search for new plugs proved fruitless, I cut a small piece of brass shim, folded it in two and inserted it into the plug. When the plug was put back on the injector, the shim made contact between the plug and injector contacts and cured the problem. I have since found new plugs with pigtails that I can splice into the wiring harness, but the temporary fix has been working fine for several months. The only casualty of the whole process, besides my patience, was the cat which succumbed to all of the various misfire events.
Apparently, whenever I would work on the engine, the injector plugs were jostled enough that the engine ran fine for a while, but then the contact eventually became intermittent again. Hopefully this will help others cure this simple but perplexing problem if they are experiencing random misfires on a higher mileage Civic.
Tom
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