Misfiring at 5,500 rpm or higher with little to no engine load - Page 3 - BMW M5 Forum and M6 Forums
E39 M5 and E52 Z8 Discussion 1998-2003 Advertiser's Forum

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post #21 of 47 Old 10th April 2019, 01:53 AM Thread Starter
SupercarFreak
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Update:


Replaced all 4 02 sensors. Cleaned all 8 VANOS solenoids and replaced seals. Test drove vehicle with 1/4 tank of gas, misfire @ 5,500 rpm in 2nd gear like clockwork. Same faults returned-


C4- Misfire Cylinder #1
C9- Misfire Cylinder #6
CC- Misfire multiple cylinders
95- Misfire w/ empty fuel tank


I restarted car, drove until I had about 1/8th tank. Poured entire bottle of RedLine SI-1 complete fuel system cleaner into tank and then a full tank of Shell 93. Drove normally for like 5 miles. Next 3 miles I ran in 2nd gear at 6,000 rpm and no matter what I did I couldn't get the car to misfire or deactivate cylinders. I find it hard to believe fuel system cleaner cleaned injector nozzles within approx. 10 miles.



I already have a new fuel filter and pressure regulator on the way. Do you guys think this is an indicator of a dying fuel pump if the car runs perfect now with a full tank?


Thanks.
Alex
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post #22 of 47 Old 10th April 2019, 07:52 PM
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I give you a pass on fixing it, but I am sending you to summer school for adaptions. LMAO
When you started the car after the first repair the adaptions were cached as the cars baseline. You needed to drive the car miles, 50 will get you somewhere, but 100 will get you 50% there. You also needed to restart the car so the new baseline would be cached, so as your new adaptions were written they would become the cache.
Just as a general rule do one thing then drive 100 miles with a few restarts to allow the new baseline to have the most effect.
We see when someone has a rich code and they change MAFs or O2s that the car can throw a lean code on the first or second start until the new baseline is in the computer.
BTW summer school is not so bad you just have to drive it like you stole it for sometime.

Last edited by Sailor24; 10th April 2019 at 07:54 PM.
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post #23 of 47 Old 10th April 2019, 08:06 PM Thread Starter
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Originally Posted by Sailor24 View Post
I give you a pass on fixing it, but I am sending you to summer school for adaptions. LMAO
When you started the car after the first repair the adaptions were cached as the cars baseline. You needed to drive the car miles, 50 will get you somewhere, but 100 will get you 50% there. You also needed to restart the car so the new baseline would be cached, so as your new adaptions were written they would become the cache.
Just as a general rule do one thing then drive 100 miles with a few restarts to allow the new baseline to have the most effect.
We see when someone has a rich code and they change MAFs or O2s that the car can throw a lean code on the first or second start until the new baseline is in the computer.
BTW summer school is not so bad you just have to drive it like you stole it for sometime.
LOL. You’re right about adaptations. I should have given them time to calibrate. But I’m curious as to what you think fixed the problem? The 02 sensors?

I’m wondering if the full tank of gas is masking a weak fuel pump.
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post #24 of 47 Old 10th April 2019, 09:14 PM
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Before throwing a bunch into it, shotgunning in troubleshooter's lingo, you need to just drive it normally for a bit. Run the tank down to about 1/4 or 1/8, refill the tank and drive it some more. Throughout these two or so tanks, do a few pulls and monitor operation. If the problem persists, then we can talk more.

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post #25 of 47 Old 10th April 2019, 09:54 PM Thread Starter
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Quote:
Originally Posted by josiahg52 View Post
Before throwing a bunch into it, shotgunning in troubleshooter's lingo, you need to just drive it normally for a bit. Run the tank down to about 1/4 or 1/8, refill the tank and drive it some more. Throughout these two or so tanks, do a few pulls and monitor operation. If the problem persists, then we can talk more.
You’re right- this is good advice. I just need to keep driving it before I condemn the fuel pump 🙂
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post #26 of 47 Old 11th April 2019, 01:41 AM
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... and then change the pump! If its got a lot of miles on it its when, not if it fails :-)

Interesting to see if issue comes back as fuel level lowers, I reckon it will.

Simon
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post #27 of 47 Old 11th April 2019, 01:54 AM Thread Starter
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... and then change the pump! If it’s got a lot of miles on it it’s ‘when’, not ‘if’ it fails 🙂

Interesting to see if issue comes back as fuel level lowers, I reckon it will.

Simon
Interestingly enough, got the car to misfire numerous times today at ~6,000 rpm with 3/4 tank left.

Regardless, fuel filter is going in once I get the new pressure regulator. It’s from 2003- just like the fuel pump 😉
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post #28 of 47 Old 11th April 2019, 04:40 PM
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I thought it was gonna be fuel pump and still might be but the fact that the codes are always cyls 1 and 6 and at high rpm sounds like a coil problem. Have you tried swapping coil positions yet? I'm assuming you have already changed the plugs.
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post #29 of 47 Old 11th April 2019, 05:09 PM Thread Starter
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I thought it was gonna be fuel pump and still might be but the fact that the codes are always cyls 1 and 6 and at high rpm sounds like a coil problem. Have you tried swapping coil positions yet? I'm assuming you have already changed the plugs.
I swapped coils and the fault codes stayed with the cylinders. So I figured the NGK-R plugs with only 25k miles on them went bad. Put in new plugs in cylinders 1 and 6, fault codes returned.

I’m pretty lost. If the fuel pump is dying I don’t understand why it keeps setting cylinder specific fault codes.
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post #30 of 47 Old 11th April 2019, 05:47 PM
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Quote:
Originally Posted by SupercarFreak View Post
LOL. Youre right about adaptations. I should have given them time to calibrate. But Im curious as to what you think fixed the problem? The 02 sensors?

Im wondering if the full tank of gas is masking a weak fuel pump.
Your problem existed at a very low demand for fuel, but that is not to say the frequency was just right to make a dirty injector fire incorrectly.



That said changing out your fuel filter is a no brainer because they are not life time. I would wait until you decide on the pump, because the best is to change the fuel pump then run the car then change the fuel filter, the extra flow from the new pump will wash more crud to the filter. Just a personal thing but I always change the filter 50 miles or so after a pump change even if the filter is new, because all the extra crud will make it old fast.



We will never know what the cause or fix was because that chance is gone. 10 miles of a injector cleaner could clean out a marginally dirty injector, but from reading this board for so many years 1 and 6 seem to be strange indicators of small vanos issues. I think it is 6 and 1 is a ghost. They are opposite cyls in the firing order and we see a ghost code as the real misfire code is generated. No idea why,I have just seen it often, but sometimes it is the cyl 3 before.

Last edited by Sailor24; 11th April 2019 at 05:55 PM.
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