BMW 4.6 is poor acceleration and hesitation

[Aman]

Originally Posted by upallnight

Is the cat on the same side of the engine that you are having the misfire issues? If so, the cat was probably destroyed due to running too rich on that side of the engine. Unburnt gasoline enter the cat from the cylinder (s) that were misfiring resulting in the cat over heating and self destructing. You need to find out why you have the misfire or else the new cat will suffer the same fate as the old one.

One place to look is the DME. There was a guy on another forum with a BMW 540 M62 engine that had a misfire until he looked at the DME. The ignitor circuit was toast.

Thanks for the advice
Can the dme be checked by computer or does it need to be inspected visually?
Is it difficult to check?
Thanks

[upallnight]

Originally Posted by Aman

Thanks for the advice
Can the dme be checked by computer or does it need to be inspected visually?
Is it difficult to check?
Thanks

The person that posted about his misfire problem removed the DME and found a note written on the DME that one of the ignitor circuit was bad. He opened up the DME and sure enough the transistor for the ignitor circuit was burnt.

Edit found the other poster post.

Just read the posts by MrProject.

M60 misfire / idle issues

[bcredliner]

I would still check back pressure to be sure the other cat is not starting to fail and the new one shows back pressure in the acceptable range.

If any of the coils (5,6 or 8) were actually bad that could be the source cause of the cat failure as that would cause unburned fuel to accelerate cat failure. If you have the old coils they would be easy to test.

The DME reads input. One of the sources for the input are the Oxogen sensors. O2 sensors are a maintenance replacement part at 100,000 miles. It is not unusual for a sensor to fail earlier. The O2 sensor could be cause of rich condition.

Should it trace back to the DME, I found the following source that repairs DMEs. No idea if they are good or bad but maybe someone here knows. BMW DME ECU Repair

[Aman]

Cats have both been cut off
New cats are being custom built as I write
Will post a few photos soon

[upallnight]

Let us know if it fixes the original problems. You should probably replace the O2 sensors while you are in there.

[Aman]

It was 110% the cataysts
The car now flies like mad
I didn't change the oxygen sensors as the exhaust place said the cats were probably the problem

[TerminatorX5]

glad it worked out... keep an eye on the cats and possible misfires - fuel in the cats will kill them...

[upallnight]

Originally Posted by Aman

It was 110% the cataysts
The car now flies like mad
I didn't change the oxygen sensors as the exhaust place said the cats were probably the problem

Great mechanics since they couldn't figure out that the cats were breaking up and clogging the exhaust. Their reply that it was "PROBABLY THE PROBLEM" does not leave me with a warm and fuzzy feeling inside. But hey that just me.

The cats were the problem because something made the cats the problem. Mixture is controlled by O2 sensors and if you have a bad O2 sensor eventually the mixture will also destroy your new cats.

If you read the postings by MrProject he noted that he didn't want to drive the car and risk destroying the new cats until he was sure his problem was solved.

If you don't fix the problem now, you will be posting later why your new cats are clogged again.

[Aman]

Originally Posted by TerminatorX5

glad it worked out... keep an eye on the cats and possible misfires - fuel in the cats will kill them...

Thanks for all of your advice
Just out of interest what is the best way to notice a misfire (say on 1 cylinder)?
On a v8 it can be sometimes difficult to hear a slight misfire
Will it always show as check engine light?

[Aman]

Originally Posted by upallnight

Great mechanics since they couldn't figure out that the cats were breaking up and clogging the exhaust. Their reply that it was "PROBABLY THE PROBLEM" does not leave me with a warm and fuzzy feeling inside. But hey that just me.

The cats were the problem because something made the cats the problem. Mixture is controlled by O2 sensors and if you have a bad O2 sensor eventually the mixture will also destroy your new cats.

If you read the postings by MrProject he noted that he didn't want to drive the car and risk destroying the new cats until he was sure his problem was solved.

If you don't fix the problem now, you will be posting later why your new cats are clogged again.

I have an appointment on Thursday to get live diagnostics to get every thing checked including oxygen sensors voltages
Thanks for your advice
The chap I went to today only does custom made exhausts and had owned 3 x5s himself