I passed by my indy's shop today and was chatting with one of the techs about an E39 M5 he had on the lift with the right side cylinder head on the bench. Apparently it suffered a timing chain guide failure, which was repaired without incident, but running post-repair showed a misfire on #3. They did a leakdown test that confirmed a problem on that cylinder only. The #3 cylinder wall, piston, combustion chamber, and valves all look untouched and functionally identical to the others on that bank. Head gasket was normal and consistent in appearance across the bank. Valves seem to be sealing properly (he had the intake ports full of water when I was there, and the combustion chamber side was dry; exhaust was the same) At this point they were planning to send the head out to check the casting for microscopic cracks.
While I'm deeply glad that this is not my car, as I hate chasing weird problems when I just want to drive the thing, as an academic exercise I'm curious. Any thoughts about what might be going on? Ever seen something like this?
Life's tough. It's tougher when you're stupid. -John Wayne
Hi Andrej,
I don't know if you remember my M5 misfires, and the incredible saga I had, chasing them:
https://www.bimmerforums.com/forum/s...526-DME-Repair
I had leak down on one of the cylinders; but not the other. I took a chance, and listened to my boss (a Premier Master Porsche Tech), and used a wooden dowel and a hammer to thump the lifters, to attempt to free sticky lifters.
All in all, I replaced plugs, coils, had the injectors blueprinted, replaced all the lifters, the engine wiring harness. I did leak down tests, compression tests, smoke tests.....don't even remember everything.
Interestingly, the leakdown KEPT showing up on cylinder 2, until I finally found the cure : A new DME, from a used M5, virginized and mated to my EWS by Abel, including moving my tune to the new computer. No more misfires. My guess is that the coil drivers on 2 and 8 were dying?
If the shop has already tried all the basics, and still has misfires, they might want to try a DME. Although I NEVER suspect the DME, for some reason, I did, when I first started that thread. Nonetheless, I tried EVERYTHING else first.
Personally, after my own experience with my M5, I take leakdown tests with a grain of salt.
Chris Powell
Racer and Instructor since, well. decades, ok?
Master Auto Tech, owner of German Motors of Aberdeen
BMWCCA 274412
German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471
Thanks, Chris. I have only the vaguest of recollections of your misfire issues - my brain is quite schizophrenic when it comes to deciding what information to retain and what to discard, so please don't take it personally. It certainly sounds like an avenue to explore. I'll pass along your thread to them - hopefully it will help out.
Life's tough. It's tougher when you're stupid. -John Wayne
I still don't understand how an electronic issue can be responsible for leakdown. Cylinder washing from over fueling, yes but enough to permanently cause leak down and then to be corrected with electronics ? I can see why you might discount LD results.
Cracks, "microscopic" ones certainly, ain't the issue. If significant enough in block or head as to effect cylinder pressure you'd already know.
I wonder if the subject of this thread hasn't got a sticky ring.
Last edited by ross1; 07-19-2018 at 12:04 PM.
If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue
From what I remember of that interesting thread,
is that misfires kept showing up on cylinder#2.
I don't recall leakdown test failures,
but then again my memory isn't what it used to be.
https://www.bimmerforums.com/forum/s...E-Repair/page5
See post 115.
I don't have the slightest idea why the electrical / DME issue and the leakdown results correlated....ON ONE CYLINDER, (not both) for a while.
The anomalies of my own M5's issues were enough to convince me that we have to think beyond the box sometimes. (Note please that the very same car continues to torment me with blatantly simple brake issues.)
You all know the story of the plumber's pipes always leaking?
Chris Powell
Racer and Instructor since, well. decades, ok?
Master Auto Tech, owner of German Motors of Aberdeen
BMWCCA 274412
German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471
Yes Chris, thanks for the refresher course,
I ended up reading from post#115 all the way till the end.(post#177)
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