M54 rough idle and misfiring - with diagnostics
 

Hi all,

My '04 E53 M54 started to have a very rough idle and misfire one cold morning.

I found the intake boot had the standard splitting issue. Same issue as my e46.

Replaced the intake boot, but that only improved the issue, still have a slight misfire.

I tired my Bluetooth OBD2 scanner, it connects to ecu but won't read codes. Strange since it works fine on my e46.

So I took the car to a auto shop and they diagnosed it for me.
I uploaded the diagnostic pdf, you can download it from my google drive:
https://drive.google.com/file/d/1Oj1...w?usp=drivesdk
Some of the codes are old codes, eg transmission in limp mode. It's not in limp mode now, but it was before.

The report says, misfire cylinder 1,2,3,4,5 (not 6). And ignition cylinder 2 and 5. MAF and DISA.

I have:
changed the spark plugs (they were original, figured it was time for new ones)
Cleaned the MAF
Inspected the disa, flap holds vacuum fine and I can see it opening and closing when I turn the car on, so seems ok but maybe it has a vacuum leak?
Checked the intake pipes for vacuum leaks

Misfires across multiple cylinders like that sounds like a vacuum leak or possibly a fuel issue.

I would:
1. get a proper smoke test done....not a cigar and a fluid pump.

2. Check fuel pressure at the valve on the rail..should be about 50-52 psi (bar?)

Coil pack failures are common. Mine had different aged coil packs when I bought mine. Two were fairly new. Four were OEM. I replaced all 6 with a Jegs NGK set. Ohm out the coil packs see if any are way out of range from others.

Thanks for the replies.
I will try do a fuel pressure test. I remember I had to replace the little regulator on the fuel rail for my e46 years ago.

Regarding the coil packs, I have tested them and they are all the same. I get very low ohms, 0.3ohm from memory. Thats across 2 of the 3 pins. The other pins give no reading (OL). All 6 coils have identical readings.

The spark plug in cylinder 5 was a little bit brown, so I have swapped the coil pack with another cylinder. I will drive the car tomorrow and see if the browning spark plug follows the coil.

What are O2 sensors doing? MAF flow reading? Fuel trim readings?

I wish I knew, my scanner can connect to the ecu but fails to read any data :/
No idea why

Try another scanner and check fuses.