Occasional Misfire on same cylinder, not plug or coil - Page 2 - BMW M5 Forum and M6 Forums
E39 M5 and E52 Z8 Discussion 1998-2003 Advertiser's Forum

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post #11 of 20 Old 10th February 2019, 01:29 AM
TurboHugh
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Occasional Misfire on same cylinder, not plug or coil

At your mileage why not pull the injectors and get them serviced and flow tested : RC engineering used to be good at that . Iím thinking leaking injectors: do you smell raw fuel ? Say you drive and shut down:: does the exhaust or rear of the car smell like raw fuel ?


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Last edited by TurboHugh; 10th February 2019 at 01:32 AM.
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post #12 of 20 Old 23rd February 2019, 11:25 PM Thread Starter
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Update here: Pulled all the injectors, had them sent out and cleaned. Guy said they were all fine anyway as far as flow rate, atomization was improved but in general they were fine. Getting the injectors out of this motor is a total PITA, by the way, and I've done pretty much all the big E39 jobs so far. The little clips on the injector electric connectors are one of the most maddening items on the whole car.

Anyway, put a fresh tank of gas in, gave it the business and bam, same code. C5, misfire w/fuel cutoff Cyl #2. DAMN! Also got a D5, Cyl 5 misfire during warmup and a 95 - Misfire w/empty fuel tank but the last two codes I'm guessing are simply from starting the car with empty fuel rails after the injector reinstall and are unrelated.

I'm done with this thing at this point, giving it to a shop to take a look at as a next step. I'm out of time and patience.

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post #13 of 20 Old 24th February 2019, 12:17 AM
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I think youíll get some codes first start occasionally... have you checked injector / coil wiring continuity back to DME?

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post #14 of 20 Old 24th February 2019, 01:45 AM
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Same code no matter what you do is looking very bad. Time for a compression check and leakdown test.
Clear the codes and make sure the 95 is not seen again, it points in another direction, maybe a better direction than where you sit now.
BTW those clips don't have to be removed/released they pop off and on with a little bit of force.
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post #15 of 20 Old 1st March 2019, 02:41 PM Thread Starter
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Update: Shop cleared the code and replicated the problem, again same cylinder. Compression test looks good. Today the plan is to do another compression and leakdown test with another gauge just to be sure. Suspecting perhaps high rpm valve float from weak spring or sticking valve or something like that. Shop noted that car pulls hard and runs well otherwise.

Big question: If heads have to come off and be serviced at what point do I consider just buying a used engine from Clemster and swapping it in myself? I'd have a whole spare engine worth of parts then. My guess is from here on out any fix will be thousands of dollars. This isn't a throw-away car regardless of KBB value and miles so I'm "in" either way.

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post #16 of 20 Old 1st March 2019, 03:59 PM
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My thought is not that it is a mechanical problem because it is not constant. Best guess is your DME is failing but the only real way to figure that out is rule everything else out. Ya I would get in touch with Clem and see if he has used DMEs.
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post #17 of 20 Old 3rd March 2019, 04:58 PM
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post #18 of 20 Old 8th May 2019, 08:45 PM Thread Starter
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Quick follow-up here is that the "fix" was to put in another entire engine from Clemster, which I did myself. Runs like a charm now, LOL. This rules out the DME.

Old engine is sitting in the corner of the garage to be rebuilt one day.

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post #19 of 20 Old 9th May 2019, 01:54 AM
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That is a pretty "fix all" fix.Well done, there is a chance you might have had the beginning of a cylinder to cylinder head gasket leak, besides think of all the spare parts you have.
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post #20 of 20 Old 9th May 2019, 09:25 PM Thread Starter
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I figure at this point in E39 M5 ownership it makes sense to have, you know, an entire other engine laying around. Bunch of spare parts, maybe a fresh rebuild one day if not, etc. it's a win-win. Of course the only main negative is that for a 4.9L motor it's ENORMOUS physically and takes up quite a bit of space in the garage. BMW really shoehorned that thing into the E39.

The motor swap was quite the experience, a culmination of about 10 years of BMW DIY wrenching. Every single skill, coping mechanism, and tool was used. There were definitely some low points in the process where I was ready to just kick out the jack stands, but all is well and the car is better than ever. My caretaking watch continues with this car.

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