Misfiring at 5,500 rpm or higher with little to no engine load - BMW M5 Forum and M6 Forums
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post #1 of 44 Old 28th March 2019, 05:46 PM Thread Starter
SupercarFreak
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Misfiring at 5,500 rpm or higher with little to no engine load

Hey guys. Ex-BMW mechanic of 10 years here, still canít figure this out. Iíve searched the forums and canít find a solution to the issue Iím dealing with.

í03 M5 with 70,000 miles. Bought car with 40,000 miles. Original fuel pump, filter, injectors. At 45,000 miles I replaced plugs (NGK-R BKR6EQUP), coils (OEM BMW) and boots (BREMI).

Car has DINAN exhaust and I like to hear it. Car runs absolutely perfect and smooth in all driving conditions including regular daily driving as well as beating on it.

However, under light to no engine load, 5,500 rpm or higher (usually 2nd gear) car will misfire, stumble and deactivate cylinders like clockwork. It has been doing this for a really long time and Iím tired of it. Every time I restart the car the CEL is off and itís running on 8 cylinders again.

Original fault codes:
8D- Fuel level, plausibility (I know my fuel level sensor is dying, sometimes it is very sluggish to respond but has been fine recently)
B2- Catalyst system efficiency cylinders #1-4
B3- Catalyst system efficiency cylinders #5-8
0D- PreCat 02 sensor cylinders #1-4
C4- Misfire Cylinder #1
C9- Misfire Cylinder #6
CC- Misfire multiple cylinders
95- Misfire w/ empty fuel tank

As far as I know car has original 02 sensors, cats and MAFs.

Car always gets filled with brand name 93 octane. Originally I thought the engine mapping on the Shark tune was the culprit, so I reflashed the ECU back to stock. Car still misfires.

It is throwing misfire codes for cylinder #1 and cylinder #6. I swapped #1 coil to cylinder #2 and swapped #6 coil to cylinder #5. Cleared codes, test drove. Fault codes returned and stayed with the cylinder instead of migrating with the coil so I figured spark plugs #1 and #6 were bad (even though they only had 25k miles on them).
Replaced plugs #1 and #6 with new NGK-R (again). Cleared codes, test drove. Fault codes returned- misfire cylinder #1 and #6.

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

Not sure why it's throwing code 95, all test drives done with 1/3 to 1/4 tank left.

What is going on here? Every ignition component has been replaced. If it was bad gas or a weak fuel pump or a clogged or dirty injector or weak fuel delivery wouldnít the car run like *** all of the time?

Thanks guys.
Alex
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post #2 of 44 Old 29th March 2019, 03:41 AM
josiahg52
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Quote:
Originally Posted by SupercarFreak View Post
If it was . . . a weak fuel pump or a clogged or dirty injector or weak fuel delivery wouldnít the car run like *** all of the time?
In short, no, it might not, but. . .

. . . have you checked the actual fuel level in the left and right tanks from the OBC service (secret) menu when total fuel quantity is 1/3 or 1/4 level?

Has this ever happened with a fuller fuel tank?

Also, for some reason, the standard practice of swapping coils and plugs around the cylinders often gives false positives and can lead you down a path. I know others can explain further if required.

2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim
8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
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post #3 of 44 Old 29th March 2019, 04:40 AM
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Unplug the MAFS and see how it runs. Remember you will have no IAT with the MAFs unplugged so no trashing. Second but really first either replace or repair what is going on with the O2s.
You are getting code 95 because the O2 are being seen as lean during a misfire event.
If the O2s are original just swap them out, you can't diag anything with bad O2s.
O2 have a best life span of 100k miles but a performance life of 60k, you are past that. They also have a lack of use life cycle and at 70K that has been abused, although platinum does not oxidize there is other effects that are the same when used O2s sit for extended periods.
You more than likely have several things just out of whack, not major just a tad, causing your issues. Bring one back and you will see changes but not a cure because of adaptions, but new O2 would be the smart first step, but I am guessing your MAFs are done partly also. All that plays into the vanos so if it has not had the maintenance it will act up too.
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post #4 of 44 Old 29th March 2019, 04:51 AM
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As Sailor recommended, start with replacing the 02s. The very first diagnosis I ever made of my first E39 M5's issues was bad pre-cat 02s. Indy disagreed vehemently, I made him change the 02s, and voila. They play more of a role than one would think, given that they are narrow band.

MAFs definitely should be replaced as well. They are a finicky part of the stock S62 control system.

I also would clean injectors in cylinders 1 and 6 if not all, just to be sure. A clogged injector is a quick an easy way to blow an otherwise perfect motor.

If the foregoing doesn't fix things, then check you fuel filter, regulator and pump, in that order.

Finally, check vanos function with Autologic or INPA or similar software.

--Peter
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post #5 of 44 Old 29th March 2019, 04:53 AM Thread Starter
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Quote:
Originally Posted by josiahg52 View Post
In short, no, it might not, but. . .

. . . have you checked the actual fuel level in the left and right tanks from the OBC service (secret) menu when total fuel quantity is 1/3 or 1/4 level?

Has this ever happened with a fuller fuel tank?

Also, for some reason, the standard practice of swapping coils and plugs around the cylinders often gives false positives and can lead you down a path. I know others can explain further if required.

The car has a 1/4 tank right now according to the manual gauge on the cluster, I will check the tank numbers through the secret menu tomorrow. After that, I'll fill up the tank and try to get it to misfire again. The numerous times this has happened I don't remember looking at the fuel gauge. Thanks for the help!


Quote:
Originally Posted by Sailor24 View Post
Unplug the MAFS and see how it runs. Remember you will have no IAT with the MAFs unplugged so no trashing. Second but really first either replace or repair what is going on with the O2s.
You are getting code 95 because the O2 are being seen as lean during a misfire event.
If the O2s are original just swap them out, you can't diag anything with bad O2s.
O2 have a best life span of 100k miles but a performance life of 60k, you are past that. They also have a lack of use life cycle and at 70K that has been abused, although platinum does not oxidize there is other effects that are the same when used O2s sit for extended periods.
You more than likely have several things just out of whack, not major just a tad, causing your issues. Bring one back and you will see changes but not a cure because of adaptions, but new O2 would be the smart first step, but I am guessing your MAFs are done partly also. All that plays into the vanos so if it has not had the maintenance it will act up too.

I performed the IAT sensor relocation last fall. I will order 2 new OEM precat 02 sensors. You are right, that is a great first step. If that doesn't work I'll run the car with the MAFs unplugged and see what happens. What VANOS maintenance/rebuild kit do you recommend? Thanks!


Alex
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post #6 of 44 Old 29th March 2019, 04:59 AM
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Don't be cheap get all four O2s your B2B3 codes come from the post O2 reading, those are likely Vanos being sluggish, but if you have the codes it has been sluggish a very long time so now you have carbon built up on the exhaust valves, but that is later get step one done.
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post #7 of 44 Old 29th March 2019, 05:09 AM
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Quote:
Originally Posted by SupercarFreak View Post
What VANOS maintenance/rebuild kit do you recommend? Thanks!


Alex
We use Beisan because they are a hop skip and a jump from our shop, but Dr. Vanos is just as good. Regardless, use BMW solenoid D-rings.

--Peter
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post #8 of 44 Old 29th March 2019, 05:29 AM Thread Starter
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Originally Posted by herrubermensch View Post
As Sailor recommended, start with replacing the 02s. The very first diagnosis I ever made of my first E39 M5's issues was bad pre-cat 02s. Indy disagreed vehemently, I made him change the 02s, and voila. They play more of a role than one would think, given that they are narrow band.

MAFs definitely should be replaced as well. They are a finicky part of the stock S62 control system.

I also would clean injectors in cylinders 1 and 6 if not all, just to be sure. A clogged injector is a quick an easy way to blow an otherwise perfect motor.

If the foregoing doesn't fix things, then check you fuel filter, regulator and pump, in that order.

Finally, check vanos function with Autologic or INPA or similar software.

--Peter

I'm going to assume the best way to clean the injectors is to remove them. How do you clean them once they are removed?


Thanks.
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post #9 of 44 Old 29th March 2019, 06:19 AM
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Originally Posted by SupercarFreak View Post
I'm going to assume the best way to clean the injectors is to remove them. How do you clean them once they are removed?


Thanks.
Yes. You have to remove the injectors, then send them off to an ultrasonic cleaning service.

--Peter
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post #10 of 44 Old 29th March 2019, 02:53 PM
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FWIW I used this guy for my injector cleaning and he did a great job. Very thorough and knowledgable, quick, easy to deal with. http://roschfuelinjectorcleaning.com/place-orders/

Evolve Alpha-N tune, FMU Rear Exhaust, E60 Shifter
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