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Discussion Starter · #1 ·
Hello and Merry Christmas board,

The subject is a totally stock 2001 M5 with just 50k gentle miles on the clock. About a month ago I got 'er back from a local BMW specialist garage with a rebuilt passenger side VANOS mechanism, and shortly thereafter a new driver's side MAF sensor (pooped out a few days later on its own with distinct, non-VANOS symptoms). After that things were golden, with proper performance and no SES light, although the technician advised that the SES light might be back with a possibly failing cat. But, that did not manifest itself, so I figured the bad MAF had been throwing things off a bit downstream. I was pretty psyched after battling a frequent SES and intermittent VANOS issues for a year, finally to have everything sorted.

The other night while driving home, performance was fine, but I thought I heard a little extra growl from the exhaust under low-RPM acceleration. "Maybe a leak" I thought--it's the original exhaust and 10 years old now. However, all was *not* well the next day when I took her out for a short trip. We're talking embarrassing levels of smoke, nonexistent power, SES, and a stall-out at idle. I got the beast home ASAP (half a mile of this agony tops) and parked it.

So the question is, is this consistent with a bad cat, or something more nefarious? And either way, I'm thinking this is flatbed time, rather than limp-five-miles-to-service time...

Thanks,
Steve
 

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Hello and Merry Christmas board,

The subject is a totally stock 2001 M5 with just 50k gentle miles on the clock. About a month ago I got 'er back from a local BMW specialist garage with a rebuilt passenger side VANOS mechanism, and shortly thereafter a new driver's side MAF sensor (pooped out a few days later on its own with distinct, non-VANOS symptoms). After that things were golden, with proper performance and no SES light, although the technician advised that the SES light might be back with a possibly failing cat. But, that did not manifest itself, so I figured the bad MAF had been throwing things off a bit downstream. I was pretty psyched after battling a frequent SES and intermittent VANOS issues for a year, finally to have everything sorted.

The other night while driving home, performance was fine, but I thought I heard a little extra growl from the exhaust under low-RPM acceleration. "Maybe a leak" I thought--it's the original exhaust and 10 years old now. However, all was *not* well the next day when I took her out for a short trip. We're talking embarrassing levels of smoke, nonexistent power, SES, and a stall-out at idle. I got the beast home ASAP (half a mile of this agony tops) and parked it.

So the question is, is this consistent with a bad cat, or something more nefarious? And either way, I'm thinking this is flatbed time, rather than limp-five-miles-to-service time...

Thanks,
Steve
+1 on the flatbed for starters.

Since the car was just in for vanos, I would have them check seals/o-rings first.
Smoke is never good but white smoke is better than blue.
 

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Discussion Starter · #4 ·
I kinda doubt it's VANOS / solenoid rings / etc. after about 800 smooth-running miles since service, but can't rule it out either... the smoke was more whitish rather than blue, although it wasn't the fluffy white shade of burned antifreeze. I wouldn't expect any of those things to make the car feel like it had 40hp, but a blocked exhaust might.

Yah, will order up a Peake tool.
 

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Should (nearly must) replace MAFS in pairs. The exhaust note change you described is a hallmark of needing new CPS. Even after you get your Peake -- which is definitely step #1 -- if it reports a "cat" related code, be advised they are generally false positives. Truly failed cats should stink and/or rattle.
 

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Discussion Starter · #6 ·
Should (nearly must) replace MAFS in pairs. The exhaust note change you described is a hallmark of needing new CPS. Even after you get your Peake -- which is definitely step #1 -- if it reports a "cat" related code, be advised they are generally false positives. Truly failed cats should stink and/or rattle.
I've had failed CPS in the past but didn't observe a similar sound to this. None of the CPSen in the car are more than two years and 14k miles old and didn't cripple the engine when dead. Oh well. I'll do some re-searching on MAFs... not excited to buy another of the official Bosch SKU for > $400 and seem to remember there may be an equivalent Rover part.

Peake == ordered.

A friend suggested a fuel over-metering problem, based on my description of the smoke cloud. I haven't noticed any stink or rattle from the cat.
 

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open the air filters and check if there is oil in them...
+1.

You had the bank 1 VANOS rebuilt, but the bank 2 is just as susceptible. If there's oil on the filters, the air mass meter(s) are contaminated as well. The smoke is from the obvious ingestion of oil in the intake.

All things considered, this would be a pretty good situation to be in.

Good luck!
 
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