QuestionRecently my Passat (wagon) started running really rough and lost power almost immediately. I had it towed to a garage and they discovered that the car was misfiring. A compression test was completed and all the cylinders have excellent compression. The coils were swapped out in order to determine if they were bad, the misfire did not relocate. A couple cracked vacuum hoses were found, replaced and this seemed to resolve 1 of the 2 misfiring cylinders. So now I've got a single cylinder that's misfiring, nothing on the OBDII sensor other than misfire code and the injectors, mass air flow sensor, coils and plugs have all been changed out.
Any ideas?
AnswerWith all you have done, this is a tough one. Assuming the engine is good(as you stated compression good all around), it really comes down to only 2 possibilities, spark or fuel delivery.
- Spark: Did you also change the plug wires? Is the offending cylinder's wire possibly passing too close to another(inductive short?) How about the input signal to the coil; this cannot be swapped, so maybe there is a frayed, corroded, broken, or shorted connection there. Also there may be a bad sensor/signal going to the ECU, such as O2, but it doesn't make much sense if only one cylinder is affected.
- Fuel: Electrical connection to the injector, same issues as above? Restriction in the fuel rail to this injector(not likely)?
- Lastly the ECU could be bad in such a way that you get these symptoms.
Good luck and let me know what you find.
