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Discussion Starter · #1 ·
I had my cats replaced under warranty a while ago (see http://www.m5board.com/vbulletin/showthread.php?t=54366), and recently my SES light came on and has stayed on for a week or so. I haven't noticed any difference in performance, but a couple times yesterday when I got on the gas hard at higher RPMs (for driving in town in heavy traffic, 4-5K) the exhaust note was noticeably louder than normal (I have the stock exhaust). I tried to repeat it again the next chance I got (a minute or so later) but then it sounded normal, and I couldn't get it to do that again. I had thought a couple times previously that it sounded a bit louder but nothing quite so obvious, and that was before the SES light. Is it possible that I have an intermittent exhaust leak, maybe at the cats if they weren't sealed properly? Has anyone ever even heard of an intermittent exhaust leak that varied so much? Could there be any other explanation for this?

- Dave

PS: I actually kind of liked how it sounded; maybe I should get an aftermarket exhaust, but I would only want it to be louder when I got on the gas hard, and as quiet as stock otherwise.
 

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DaveK said:
I had my cats replaced under warranty a while ago (see http://www.m5board.com/vbulletin/showthread.php?t=54366), and recently my SES light came on and has stayed on for a week or so. I haven't noticed any difference in performance, but a couple times yesterday when I got on the gas hard at higher RPMs (for driving in town in heavy traffic, 4-5K) the exhaust note was noticeably louder than normal (I have the stock exhaust). I tried to repeat it again the next chance I got (a minute or so later) but then it sounded normal, and I couldn't get it to do that again. I had thought a couple times previously that it sounded a bit louder but nothing quite so obvious, and that was before the SES light. Is it possible that I have an intermittent exhaust leak, maybe at the cats if they weren't sealed properly? Has anyone ever even heard of an intermittent exhaust leak that varied so much? Could there be any other explanation for this?

- Dave

PS: I actually kind of liked how it sounded; maybe I should get an aftermarket exhaust, but I would only want it to be louder when I got on the gas hard, and as quiet as stock otherwise.

Check fault codes for CPS problem.
Regards,
Jerry
 

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gsfent said:
Check fault codes for CPS problem.
Regards,
Jerry
Ditto.. camshaft position sensor. I would put money on it.

By the way Dave, if you do a search you'll find plenty of threads on this.
 

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Discussion Starter · #4 ·
Anzir said:
Ditto.. camshaft position sensor. I would put money on it.

By the way Dave, if you do a search you'll find plenty of threads on this.
Thanks. I'm surprised that the exhaust could get that much louder because of valve timing (I assume that's what changes when the sensor malfunctions), but that does seem likely to be the problem based on other's experience.

I should have done a search first, usually I do, but I assumed that I would just get a flood of posts about aftermarket exhausts. My bad.

I guess I should have noticed a performance drop, but maybe it seemed faster than it really was because it sounded faster. :)

I scheduled an appointment at the dealer to have it checked out. I'll make sure they know to check those sensors.

- Dave
 

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Discussion Starter · #6 ·
Re: SES and louder exhaust note - UPDATE

Update:

I just talked to the service advisor and they said one of the catalytic converters went bad (this makes it the second time for both of them in the past 16 months), and they figured out what was burning them out. He said the oil separators are bad and allow oil to flow through into the exhaust, which fouls the cats.

If I'm not mistaken those separators are connected to the intake plenum, which means that it's been burning oil, although not so much that I've noticed it in the exhaust or in extra oil consumption. What else besides the cats could be affected by this?

Apparently the only codes they found were related to the bad catalytic converter, which doesn't explain the intermittent louder exhaust note, which is why I brought it to the dealer in the first place. Could they be related somehow, or could possible codes for cam position sensors be flushed out by recurring codes related to the bad cat?

The service advisor was kind enough to have the car put back together so I could use it this weekend for a trip since the parts won't be there until Monday (I don't get a loaner with the CPO). I'll see if it has more problems with the exhaust note meanwhile.

- Dave
 

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Changing CATs and the fault just keeps coming back...

Replace the oil-separators and tell them to replace all four O2 sensors before wasting money on more CATs.

I think the oil-smoke fouled the O2 sensors, and the engine has been running at the wrong AFR ever since. That eats CATs fast.

It is also entirely possible the CAT shave been ok all along and it is just the O2 sensors that are acting up, producing an AFR the CATs can not function properly with.

The exhaust sound is unrelated. It is most likely the camshaft sensors. Two of those four need to be replaced. There was a design upgrade. The old design will fail on almost every car.

It can also be the Vanos-valves, but that is far less likely than the camshaft sensor.

David
 

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Discussion Starter · #8 ·
I just got the car back for the weekend, they are waiting on parts until Monday to replace the cat and oil separators. When I expressed my concern about the cat/oil problem not likely causing the symptoms I brought it in for the service advisor said they did also find and replace a faulty camshaft sensor. I'll check when I bring it back how many have been replaced so far.

They did mention that they would replace the O2 sensor as well as the cat. I expressed concern about the other cat being partially damaged as well since it's been in there a few months under conditions that caused one to go bad in a year the last time. I'll see if they are at least willing to replace the other O2 sensor.

- Dave
 

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DaveK said:
I just got the car back for the weekend, they are waiting on parts until Monday to replace the cat and oil separators. When I expressed my concern about the cat/oil problem not likely causing the symptoms I brought it in for the service advisor said they did also find and replace a faulty camshaft sensor. I'll check when I bring it back how many have been replaced so far.

They did mention that they would replace the O2 sensor as well as the cat. I expressed concern about the other cat being partially damaged as well since it's been in there a few months under conditions that caused one to go bad in a year the last time. I'll see if they are at least willing to replace the other O2 sensor.

- Dave
There are four O2 sensors. The two front ones are involved with regulating the fuel-trim. The two rear are just for monitoring the function of the MAFs.

Your concern about the CAT is quite valid, but the CATs are covered by the eight year emissions warranty, so you need not worry. Ask the SA or BMW NA for a statment that the emissions warranty for the CATs is still valid given the oil-smoke history of this particular vehicle.

For good measure get the four O2 sensors replaced, or as a bare minimum both front O2 sensors. If the dealer acts up, and you don´t bother quarrel, it is an easy DIY job to replace an O2 sensor.

See:

http://www.m5board.com/vbulletin/showthread.php?t=54863

You just need the sensor, a torque-wrench, a crow-foot and some Never-seize paste.

If you are not too fanatic you can substitute a wrench and some common sense for the torque-wrench and crow-foot.

I would of course use my torque-wrench... ;-9

David
 
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