JColbourne
New member
Mis-fire problem[/b]
I would be grateful if anyone one would comment and/or give me any advice regarding the problem below. Apologies if it appears somewhat verbose, but I felt that if I missed anything out, the full picture would not be understood.
I have a 2003 996 C4S and current mileage is 117,907 (114,071 of those done by me as it's a business car). The car's been serviced at the relevant mileage intervals. No running problems have been encountered until the last 10 days.
On the first frosty morning of this autumn (November 1st) I started the car and immediately noticed unevenness in the engine performance on tick over. My immediate thought that this was something caused by the air temperature. The car vibrated as if there was an imbalance in the number of cylinders firing and the "Check" warning light came on as well as the "Drive to Workshop" message. On listening to the exhaust note there was a distinct "chugging" and intermittent "pop" from the nearside exhaust. The offside exhaust sounded normal. When the car was driven a short distance however, the performance did not seem to be impacted but the "lumpiness" and "chugging" persisted on tick over.
Upon underside engine inspection, a faulty coil pack was suspected. Subsequent diagnosis at an OPC indicated a coil pack problem. The condition of one coil pack was particularly poor and others were showing the signs of splitting, so all six were changed on November 3rd. It was noted at the time the work was done, that the nearside exhaust showed more emission deposits than the offside one i.e. it was blacker
All seemed well until the same symptoms, or be they not quite as severe as when they first appeared, recurred the day after the coil packs were changed. Again the performance under normal driving did not appear to be impacted. After some miles being covered the check warning light went out. This resulted in a second visit to another OPC on November 8th. The diagnosis this time indicated a problem on cylinder number 6. Consequently a different coil pack and spark plug for the cylinder were tried but the diagnosis persisted. The suggestion was that it could possibly be a broken valve spring but this I believe does not fit in with the problem being an intermittent one and only being noticeable on tick over. Whilst driving home, around 120 miles, the warning light and message did not appear but I did notice on a couple of occasions when I braked for a junction the "lumpiness" recurred but then cleared upon acceleration.
The charge from the alternator/battery connection has now been tested as part of the problem diagnosis and has been found to be below the power reading expected. It is thought that this could be having an effect on the Engine Management System and hence causing an engine malfunction e.g. causing a cylinder/cylinders to run too rich.
The other odd thing now is that the offside exhaust outlet is now blacker than the nearside one. Also when I put my hands close to the exhausts I get the impression that the offside one is running hotter than the nearside one. Photos are attached.
I'd be interested to find out if anyone has had similar experiences and would appreciate any replies that you are able to post.
Regards
John C
I would be grateful if anyone one would comment and/or give me any advice regarding the problem below. Apologies if it appears somewhat verbose, but I felt that if I missed anything out, the full picture would not be understood.
I have a 2003 996 C4S and current mileage is 117,907 (114,071 of those done by me as it's a business car). The car's been serviced at the relevant mileage intervals. No running problems have been encountered until the last 10 days.
On the first frosty morning of this autumn (November 1st) I started the car and immediately noticed unevenness in the engine performance on tick over. My immediate thought that this was something caused by the air temperature. The car vibrated as if there was an imbalance in the number of cylinders firing and the "Check" warning light came on as well as the "Drive to Workshop" message. On listening to the exhaust note there was a distinct "chugging" and intermittent "pop" from the nearside exhaust. The offside exhaust sounded normal. When the car was driven a short distance however, the performance did not seem to be impacted but the "lumpiness" and "chugging" persisted on tick over.
Upon underside engine inspection, a faulty coil pack was suspected. Subsequent diagnosis at an OPC indicated a coil pack problem. The condition of one coil pack was particularly poor and others were showing the signs of splitting, so all six were changed on November 3rd. It was noted at the time the work was done, that the nearside exhaust showed more emission deposits than the offside one i.e. it was blacker
All seemed well until the same symptoms, or be they not quite as severe as when they first appeared, recurred the day after the coil packs were changed. Again the performance under normal driving did not appear to be impacted. After some miles being covered the check warning light went out. This resulted in a second visit to another OPC on November 8th. The diagnosis this time indicated a problem on cylinder number 6. Consequently a different coil pack and spark plug for the cylinder were tried but the diagnosis persisted. The suggestion was that it could possibly be a broken valve spring but this I believe does not fit in with the problem being an intermittent one and only being noticeable on tick over. Whilst driving home, around 120 miles, the warning light and message did not appear but I did notice on a couple of occasions when I braked for a junction the "lumpiness" recurred but then cleared upon acceleration.
The charge from the alternator/battery connection has now been tested as part of the problem diagnosis and has been found to be below the power reading expected. It is thought that this could be having an effect on the Engine Management System and hence causing an engine malfunction e.g. causing a cylinder/cylinders to run too rich.
The other odd thing now is that the offside exhaust outlet is now blacker than the nearside one. Also when I put my hands close to the exhausts I get the impression that the offside one is running hotter than the nearside one. Photos are attached.
I'd be interested to find out if anyone has had similar experiences and would appreciate any replies that you are able to post.
Regards
John C
