Shipkiller
Veteran
My wife's 2003 Z4 (66K miles) developed a major misfire on a drive we were taking.
Hobbled home and quickly diagnosed it to be a bad coil on cylinder five and it was throwing a code. The misfire went from minor to major and bounced between the two.
When the misfire as a minor one, the SES light will just light up and stay lit. When it progress to a major misfire, the SES light would BLINK, just like it was supposed to for a major issue. When the misfire went back to a minor misfire the SES light would stop blinking and stay lit.
I am stating this so you understand how to read the error indications. The car will tell you a lot of info if you remain calm and read the car... if you loose your mind like a little girl (oh my god, my car is broke....) then you loose a golden chance to figure these things out.
Moved the coil to cylinder one and the code changed to that cylinder. Ok, it's bad.
Ordered a new coil and replaced it. Now all the codes are cleared and not returning but there is a major stumble when you semi-aggressively get on the throttle. Using a smooth linear application of throttle, there would be no stumble. This would happen at any RPM.
I checked a lot of other things:
Cleaned the MAF
Check Fuel pressure at the fuel rail
Check the DISA
etc. etc. etc.
and then decided that I was over analyzing this problem.
Go back to the original problem. There were NO ISSUES until cylinder five's coil died. It has to be another coil or group of coils. Did not want to spend the time to figure this out so I bought five more coils.
All coils have been replaced and now it drives like the finely tuned machine it is.....
I have a theory on what happened.
Fact: What I do know it that the MS45 ECM (sometimes called the ECU) individually controls each coil. The ignition is monitored by the ECM via the secondary ignition feedback circuit and Crankshaft Position/RPM Sensor. If a Misfire fault is present, the “Malfunction Indicator Light” (SES) will illuminate when the specific criteria is achieved and the ECM will deactivate the corresponding fuel injector for that cylinder. Engine operation is still be possible.
The ECM must determine misfire and also identify the specific cylinder(s). The ECM must also determine the severity of the misfire and whether it is emissions relevant or catalyst damaging based on monitoring crankshaft acceleration.
• Within an interval of 1000 crankshaft revolutions, the ECM adds the the detected misfire events for each cylinder. If the sum of all cylinder misfire incidents exceeds the predetermined value, a fault code will be stored and the “Malfunction Indicator Light” will be illuminated.
• If more than one cylinder is misfiring, all misfiring cylinders will be specified and the individual fault codes for each misfiring cylinder, or multiple cylinders will be stored. The
“Malfunction Indicator Light” will be illuminated.
Speculation: With 66K miles on the engine, I think that the coils were weak but not weak enough to exhibit any driving issues. This car was built in Oct of 2002, so the coils are eight years old. When cylinder five died, it stressed coils six and four. This weakened them even further. So when I moved the bad coil to cylinder one to prove the faulty coil, the same process happened again. At least four maybe five coils are now so weak that the spark-plugs are not generating enough spark to ignite the fuel under heavy acceleration (the injectors spray more fuel) but not bad enough to cause a misfire or throw a code. So I had to replace all six coils.
This possible explanation does not mean you should never move a coil for troubleshooting purposes. Just be aware of it...
Hobbled home and quickly diagnosed it to be a bad coil on cylinder five and it was throwing a code. The misfire went from minor to major and bounced between the two.
When the misfire as a minor one, the SES light will just light up and stay lit. When it progress to a major misfire, the SES light would BLINK, just like it was supposed to for a major issue. When the misfire went back to a minor misfire the SES light would stop blinking and stay lit.
I am stating this so you understand how to read the error indications. The car will tell you a lot of info if you remain calm and read the car... if you loose your mind like a little girl (oh my god, my car is broke....) then you loose a golden chance to figure these things out.
Moved the coil to cylinder one and the code changed to that cylinder. Ok, it's bad.
Ordered a new coil and replaced it. Now all the codes are cleared and not returning but there is a major stumble when you semi-aggressively get on the throttle. Using a smooth linear application of throttle, there would be no stumble. This would happen at any RPM.
I checked a lot of other things:
Cleaned the MAF
Check Fuel pressure at the fuel rail
Check the DISA
etc. etc. etc.
and then decided that I was over analyzing this problem.
Go back to the original problem. There were NO ISSUES until cylinder five's coil died. It has to be another coil or group of coils. Did not want to spend the time to figure this out so I bought five more coils.
All coils have been replaced and now it drives like the finely tuned machine it is.....
I have a theory on what happened.
Fact: What I do know it that the MS45 ECM (sometimes called the ECU) individually controls each coil. The ignition is monitored by the ECM via the secondary ignition feedback circuit and Crankshaft Position/RPM Sensor. If a Misfire fault is present, the “Malfunction Indicator Light” (SES) will illuminate when the specific criteria is achieved and the ECM will deactivate the corresponding fuel injector for that cylinder. Engine operation is still be possible.
The ECM must determine misfire and also identify the specific cylinder(s). The ECM must also determine the severity of the misfire and whether it is emissions relevant or catalyst damaging based on monitoring crankshaft acceleration.
• Within an interval of 1000 crankshaft revolutions, the ECM adds the the detected misfire events for each cylinder. If the sum of all cylinder misfire incidents exceeds the predetermined value, a fault code will be stored and the “Malfunction Indicator Light” will be illuminated.
• If more than one cylinder is misfiring, all misfiring cylinders will be specified and the individual fault codes for each misfiring cylinder, or multiple cylinders will be stored. The
“Malfunction Indicator Light” will be illuminated.
Speculation: With 66K miles on the engine, I think that the coils were weak but not weak enough to exhibit any driving issues. This car was built in Oct of 2002, so the coils are eight years old. When cylinder five died, it stressed coils six and four. This weakened them even further. So when I moved the bad coil to cylinder one to prove the faulty coil, the same process happened again. At least four maybe five coils are now so weak that the spark-plugs are not generating enough spark to ignite the fuel under heavy acceleration (the injectors spray more fuel) but not bad enough to cause a misfire or throw a code. So I had to replace all six coils.
This possible explanation does not mean you should never move a coil for troubleshooting purposes. Just be aware of it...
