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E90 N46 Misfire cylinder 1 - Strange behaviour
05-17-2018, 09:31 PM (This post was last modified: 05-17-2018 09:33 PM by Willisodhiambo.)
Post: #1
E90 N46 Misfire cylinder 1 - Strange behaviour
An E90 N46 engine with 76k on the clock. Car was involved in rear collision and was repaired. A week or so later it developed a misfire.

When it was brought to me we pulled the coils. No 1 coil smelt like it was burnt. Replaced with new. Car run fine after. Faults were Random misfire, cylinder 1 misfire and Injection cylinder 1.

After one week problem was back!!! Swapped all coils, plugs and injectors. We put the car back, cleared codes. It run fine. Three days later owner called to report oil leak. CCV pipe to head cover was loose. Put it back in and an hour later the misfire returned!!

Code the same, cylinder 1 but there is also the "misfire several cylinders" code. We are stumped. Trim for bank one almost 2.0. Strangely it stays over 1.7 even with throttle open over 50%! Misfire starts immediately with startup.

I now want to disconnect CCV and block it to see whether trim changes and whether misfire persist. Next will be a compression test on cylinder 1. I however think its an electrical problem with the one week good then bad behaviour. Checked injector pulse from DME, good, replaced DME, no change!!

Any ideas? I am avoiding parts replacement without nailing the cause first unless everything fails.

Does the "several misfires" point to anything? There is no way the DME can know what is faulty in a misfire situation. It resolves to cutting fuel and lets you probe further after trying to pin the cylinder causing it? Could it me a multiple misfire situation? If it is why is cylinder 1 logged ALWAYS?
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05-17-2018, 09:53 PM
Post: #2
RE: E90 N46 Misfire cylinder 1 - Strange behaviour
check cylinder pressure 1-2-3

engine roughness

spark plug condition
send me pm and i can help you
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05-18-2018, 02:19 AM
Post: #3
RE: E90 N46 Misfire cylinder 1 - Strange behaviour
The coil is powered by a 12v supply on pin 3, and grounded by the ECU on pin 1 to activate it.
Check to see if pin 1 of the coil plug is permanently shorted to ground.
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05-18-2018, 02:40 AM
Post: #4
RE: E90 N46 Misfire cylinder 1 - Strange behaviour
Would have to be intermittent short or car would not run well after replacing coil.

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05-18-2018, 03:29 AM
Post: #5
RE: E90 N46 Misfire cylinder 1 - Strange behaviour
check for air leaks and if it has some kind of disa valve under intake,these are common probs...
you can check if you open the thing that you pour oil in engine(i dont remember the word) when engine runs to check if it makes difference...if not,you have internal air leak that can cause misfiring too...

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 Thanks given by: diagnostix
05-18-2018, 06:17 AM
Post: #6
RE: E90 N46 Misfire cylinder 1 - Strange behaviour
Thanks guys. Checked CCV by removing and blocking intake pipe, then removed O2 sensor to check CAT status. No change.

Tomorrow ill check again for spark and compression test and report.
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05-19-2018, 12:22 PM
Post: #7
RE: E90 N46 Misfire cylinder 1 - Strange behaviour
If all is 100% ok, open valve cover and check the vvt and the excentric shaft... also the bearing
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05-20-2018, 06:08 PM
Post: #8
RE: E90 N46 Misfire cylinder 1 - Strange behaviour
(05-19-2018 12:22 PM)Bibobabo Wrote:  If all is 100% ok, open valve cover and check the vvt and the excentric shaft... also the bearing

Will do today. Spent day with it
1. Checked ignition circuitry using wiring diagram. All good, grounds good. DME to coils wires ok
2. DME to injector wires all ok

Misfire is now permanent in cylinder 1 and injection is cut off.

Will check valvetronic shaft. Can a faulty crankshaft sensor or wheel cause this? Remember the one week good then bad intermittent behaviour before
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