BMW 4.6 is poor acceleration and hesitation

[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

[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 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

[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 will check for other issues, but its useful to note that cats can sometimes fail due to age
http://www.xoutpost.com/members/sethhatfield.html also advised me this is what happened to him when he wrote his experiences in this thread (page 6 I think)

[sethhatfield]

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

Change the O2 sensors as a precaution. Its always a good idea. You can do it yourself easily/cheaply and the mileage usually always improves. I had already changed mine last year so they were fine.

They won't cause a SES light until they are completely inoperative even though they are feeding the computer inaccurate readings.

[Aman]

A few photos: