BGM1

Background: I had a 2007 E60 N52 6-speed manual (BMW1) for several years, having the typical issues and repairs as time went on. Hit black ice in a 20 car pile up last fall (2010). Relatvely minor damage, but enough to total it.

Bought another 2007 E60 N52 Automatic (BMW2) soon thereafter, but this one has far fewer options. 87K miles on it now.

Two weeks ago, starter failed on BMW2. I replaced it without issue (already experienced same with BMW1). I also noticed the crankcase vent hose (at the back of the motor) was broken - replaced this on BMW 1 also. Ordered replacement.

BMW2 also needed oil change, so oil and filter ordered.

Today, all was fine, until entering a highway, when I stepped on it hard (likely downshifting two gears, but I wasn't paying attention to it at this point). I happened to notice a large cloud of smoke in the mirror. Engine noticably running rough at times, not at others. Connected code scanner to find P0304, Cylinder 4 misfire detected. Experienced same symptom on BMW1 some time ago, bought a set of used ignition coils, replaced the coil on the indicated cylinder, and all was well from there forward (again, BMW1).

Symptoms persisted today on the hour drive home in BMW2. Cruising along, no problems were obvious. Accelerating slightly for 1 gear downshift, all seemed fine. Each time with hard acceleration causing a two gear downshift, a VERY large cloud of smoke was emitted. No apparent change in MPG on the hour drive home.

Had already planned to change the oil and replace the vent hose today, so undertook that, along with the swap of ignition coils on cylinders 3 and 4 to prove code change to cylinder 3.

On attempt to restart car, multiple times, the sequence is: push start button, engine cranks over, RPMs climb to just above 1K, engine stalls (maybe 1 second elapsed). Engine seems to be starting, but immediately stalls. No codes are reported.

Swapped the two ignition coils back to see if they were keyed into the electronics (BMW1 experience says no issue swapping in new coils, or switching two coils), but same symptoms persisted.

My best guess is that I bumped some wiring at the rear of the engine while disconnecting the vent hose cable; it's an absolute pain to get to it to release the connector retention clip.

Ran out of daylight, so done for the day.

Questions:
1) At this point, I assume (yeah, I know) that it was a bad coil causing the rough running and smoke clouds. I have more ignition coil spares (from BMW1 repairs), so this problem should be easily fixed. Are their other causes of the smoke cloud symptoms?

2) What might I have bumped to cause the engine to stall immediately after start?

donpb

You could have easily bumped a brittle hose.

BGM1

donpb: Yes, they are brittle after the years and miles, and I might have cracked it when replacing the starter a few weeks ago. Regardless, it's fixed now.


Someone posted a suggestion on another forum. It identified the problem. Here's my reply:


I disconnected the "Hot-film air mass meter", P/N 13627520519, and the engine now starts right up but runs rough for several seconds without it. Took it for a drive and it runs acceptably. Part is on order.

And it does make logical sense. Without the airflow measurement, under hard acceleration, it dumps in the fuel to prevent a lean condition, and produces a massive smoke cloud. Now I know how to compete with the diesel trucks when the need arises! lol

It's sad they don't default to a rich mixture and let you start the engine when it fails, and alert the problem. They don't even throw a code.

But disconnecting the sensor allows it to start, and to throw codes P0102 ("Mass or Volume Air flow Circuit low input") and P0113 ("Intake Air Temperature Circuit High input").


I still don't think it's likely that this failed sensor caused the P0304 ("Cylinder 4 Misfire Detected"), but maybe. I did swap the coils on cylinders 3 and 4, so if I see the problem on cylinder 3 now, I'll know it's the coil and replace it with one of the used ones I got for BMW1 years back.

donpb

I had the same problem right after I replaced my Starter.

I thought I must have broken a hose, but I'm very very careful. I barely touched those hoses. But when they get brittle, the slightest bump is more than enough to cause a tiny leak.

Mine ended up being the crankcase vent hose.

Leaks will usually cause misfires due to the ECU trying to compensate for the leak.