Multiple cylinder misfire :(

[Amos]

Hello all,
My M3 developed an issue and I am looking for some guidance and input


Car was sitting for a for a couple of months, no issues prior to this. Battery died while sitting - it's an Antigravity lithium battery. I charged it up and went for a drive, everything was fine. Parked for 10 mins to go into a store, started the car back up and it was misfiring with loss of power. Turned it off, turned it right back on and it drove fine on the way home. Thought some electric gremlins due to low battery, but I was not so lucky.

Next time I drove the car, it drove fine for about 45 minutes and then started misfiring and threw a check engine light when getting off the highway.

Restarting the car didn't fix the issue, but after about 1 hour of cool down, it started right back up and ran smoothly and I made it home.

Scanned for codes:

• P1342 → misfire cylinder 2
• P1344 → misfire cylinder 4
• P1341 → Multiple cylinder misfire with fuel cut off
• P1345 → misfire cylinder 2 with fuel cut off
• P1343 → misfire cylinder 1 with fuel cut off
• P1351 → misfire cylinder 5 with fuel cut off
• P1353 → misfire cylinder 6 with fuel cut off
• P0316 → misfire during start
• P0305 - Cylinder 5 misfire
• P0301 - Cylinder 1 misfire
• P0306 - Cylinder 6 misfire
• P0300 - Random/Multiple cylinder misfire

While the car was misfiring, revving the engine above 2K RPM made it smooth and it drove fine, no loss of power but kept misfiring at idle

So I did a dumb thing and asked ChatGPT who seems convinced it is a failing crankshaft sensor that gets worse when warmed up. Put a genuine BMW crank sensor in it but it didn't fix the issue. The old sensor was caked with oil and leaking around the O ring so not a total waste at least.

After replacing the sensor, took it for a drive. Again, the issue started only after the engine was warm, about 30 mins of driving or so. No codes at first. Restarted the engine but still misfiring.

One slight difference is when it started misfiring after start up, I revved it to 2K and it smoothed out and stopped misfiring at idle completely. Drove home and got come codes Pending.

Today's codes:
P1350 - Misfire during start Cylinder 5
P1344 - Misfire during start Cylinder 2
P0316 - misfire during start

No change in misfiring with MAF disconnected.

My next step is to smoke test for vacuum leak (my long term fuel trims are +10 on both banks although they have been that way for a couple of years now), then INPA to monitor the camshaft sensors.

Coil packs are fairly new, genuine BMW (one failed a few years back so I replaced all 6). Fuel pump also was replaced a few years ago.

Anyone with some experience with something like this?

[Amos]

So INPA code scan proved useful. In addition to all the misfire codes I saw in OBD scan , it also had this error with over 20 occurrences

Error 52 — Zuendspule 5 (Ignition Coil 5) — Primaerkreis (Primary Circuit Fault)

Not sure how one bad coil causes other cylinders to misfire but will replace and go from there

[BMWfanz]

Maybe headgasket blown between cylinders

[bigjae46]

I'd throw some spark plugs at it first. Fuel pressure? How old is the fuel filter?

Beyond that, maybe a compression test? Not sure what the correct order is to diagnose...this is when I start pulling out the hammers and pry bars...lol

[Slideways]

What are you using to scan codes?

[sapote]

So I did a dumb thing and asked ChatGPT who seems convinced it is a failing crankshaft sensor that gets worse when warmed up. Put a genuine BMW crank sensor in it but it didn't fix the issue. The old sensor was caked with oil and leaking around the O ring so not a total waste at least.

The M3 crank sensor is indestructible -- I have not heard a single case of a bad sensor electrically.

Get a csv log file using obd dongle (BluePeak) and OBDFusion app with hot engine at idle for 3 minutes longer minimum with these parameters: rpm, intake temp, coolant temp, MAF in g/sec, all 4 o2 sensors, all 4 fuel trims. Upload the csv file to datazap.me for it to plot the data graphs then post the link here for us to review, something like this example (325i engine)

https://datazap.me/u/sapote/logs/wc3cvabf113rd1yxwoz7ssxs?channels=8&sizes=100&sc=13

[ATB88]

The M3 crank sensor is indestructible -- I have not heard a single case of a bad sensor electrically.

Get a csv log file using obd dongle (BluePeak) and OBDFusion app with hot engine at idle for 3 minutes longer minimum with these parameters: rpm, intake temp, coolant temp, MAF in g/sec, all 4 o2 sensors, all 4 fuel trims. Upload the csv file to datazap.me for it to plot the data graphs then post the link here for us to review, something like this example (325i engine)

https://datazap.me/u/sapote/logs/wc3cvabf113rd1yxwoz7ssxs?channels=8&sizes=100&sc=13

Just last week I got an EML and pulled codes that indicated bad crank sensor :')

[sapote]

Just last week I got an EML and pulled codes that indicated bad crank sensor :')

This doesn't mean the crank sensor is bad. The sensor can be easily tested: measure the AC voltage across the sensor 2 wires while passing a magnet across the sensor tip, this should generate a pulse. using a screwdriver blade will work too but the generated voltage is smaller.

[ATB88]

This doesn't mean the crank sensor is bad.

curious -- what else do you think it could be?

[sapote]

curious -- what else do you think it could be?

* mistakenly having double o-rings causing wider air gap between sensor and timing tooth
* sensor connector pins with higher resistance, broken wire
* DME connector pins corroded, DME pcb board damaged.

Using an oscilloscope to capture the sinusoidal signal waveform at the 2 pins at the DME for the crank sensor with engine running, it should be a clean sinewave.

[CrookedCommie]

I'd start with new coils and spark plugs and continue to diagnose from there. Sounds like coils, they start failing when hot.