I have a 2008 528i. Ignition coil #2 fails consistently. After replacement the new one may last a year, a few months or even less. I’ve changed the plugs, I’ve purchased replacement coils from different suppliers and the problem persists. I just put a new coil in this week and had a couple misfires just today.
Any idea what could be causing the coils to fail on the same cylinder repeatedly.
There are a couple of things to check:
- the engine harness connector for coil #2
- the engine harness for cylinder #2
- the metal oxide field effect transistor (MOSFET) (in the engine computer) that provides the ground to coil #2*
- the spark plug in cylinder #2.
*The coil has 12VDC whenever the ignition switch is in either the run or start position. The DME provides the ground to fire the coil at the appropriate time.
MOSFETs are very “rugged” components but they do go bad. bmwdirtracer chased 2 misfires in his E39 M5 fir months. He even replaced the entire engine harness. Turned out that the MOSFET for each misfiring cylinder was bad.
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Crankshaft speed changes slightly after a cylinder fires and the DME uses this to detect misfires. I recall reading about a problem where the DME incorrectly reported cylinder misfiring.
Your firing order is 1-5-3-6-2-4.
I would move coils 6 & 4 to cylinders 5 & 3 to get them as far from cyl 2 as possible and recheck codes. This might be an issue with coils 4 or 6.
Last edited by pshovest; 12-14-2018 at 11:29 AM.
I really appreciate the comments all. Gotta sort this out, it’s personal now...
What brand coils are you using? OEM updated Delphi? Bosch or some Chinese junk?
ASE and BMW Master Certified Technician
I was buying cheap crap off Amazon but just bought a new coil from PepBoys, not sure the make. Now I’m getting more misfires, especially under load. Error codes say both cylinder 5 and 2 are misfiring. I pulled the ECU and tested the Mosfet prongs with a meter and they appear good, no shorts.
Is there any common associated between 5 & 2? Next I plan on cleaning all the fuel injectors and moving them to other cylinders. Any other suggestions?
Last edited by IJuggernaut; 12-23-2018 at 07:53 PM. Reason: Typo
Unfortunately that's not a reliable test, if the MOSFET(s) were shorted the cylinder would never fire at all.
Cyl 2 & 5 are exactly 360 crankshaft degrees away from each other in the firing order. This suggests the crank position sensor can't read a tooth on the crankshaft gear.
How many miles?
I would check compression.
Do misfires disable the cylinder until restart or do they just cause rough acceleration?
When do the misfires occur? idle? part throttle? WOT?
Are there any other codes?
If the misfires are severe enough the DME will disable the cylinder completely. This prevents catalyst damage by not putting raw fuel thru the cat. We need to better understand how many cylinders are misfiring. I would run the car real hard, at least 5500 rpm at WOT in second gear, pull over read codes without shutting engine off. Do cylinders other than 2 & 5 have misfires? Then shut off and restart, the misfires should clear until you drive it hard again.
Tested as prescribed after clearing all codes. Was running good, took it to 5500 rpm, had misfire in Cylinder 5 only. Engine kept running rough, cylinder was not firing. Shut down, restarted and engine was running smooth with 5 firing.
Have I been chasing an issue in Cylinder 2 all this time that was actually really #5?
Don't know if this was really cyl 5 all along. Classic misfire that clears on restart. Electrical misfires are more likely at high engine loads. Good news is that cyl 2 is not misfiring. You may simply have another bad coil. Either replace cyl 5 coil with amazon coil or move a good coil to cyl 5. Keep us posted. I'm real curious if the amazon coil will work on cyl 5.
Replaced coil #5 with a Bosch part. Tested at 5k RPM and had no issues for 1 day. Today, I was merging onto the freeway and had several misfires, engine light came on. Was riding rough for a couple miles but it then self resolved and the engine light cleared and car ran well, all without a restart. When I checked the error codes I got a “pending misfire cylinder #2”. This is not the usual “confirmed misfire” code where the engine light stays on.
Swap coils 2 & 5 and retest.
If engine still misfires, check #2 compression. If OK replace #2 injector.
Might try a tank or two of Techron before changing injector.
Changed fuel injector #2 and cleaned the rest. Ran great first time out. Hope it continues, fingers crossed.
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