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Discussion Starter #1 (Edited)
For as long as I can remember, my 03 M5 has, more often than not, had bad exhaust smell (rich/rotten egg smell). When this condition is present, there is always a loss of power and stumbles/stutters at low RPM (off idle to ~2500) associated.

I don't enjoy bringing the car in for service much, so I usually only bring up these complaints when my car goes in for regular services. My car went in for the first brake flush (second year anniversary) last month, so I had my SA look at the exhaust smell/power loss issue among other little things.

They had my car most of the week. My SA said there's no fault codes. The only thing read from the computer was a "cat conversion efficiency" (or something). He stated it is a code he has never seen before. So a PUMA (spell? the BMW support line) case was opened. At first he thought the cats will be replaced, but per BMW they flashed my car with a newer software. My car was built in 3/05 and I thought it already had the latest software?

I had the car for 2 weeks before I brought it back in. I didn't drive it all that much, but the bad exhaust/low RPM stumble is there ALL the time now! They've now had my car for 1 1/2 week and still no answer. Everytime I asked my SA he says the tech thinks it drives fine, but he opened another PUMA case anyway. I usually have to repeat myself several times - I told him drive the car around 40-50 mph on 6th gear, and floor it. The car will not want to move; it feels like the car is in 1 gear too high on low RPM.

Tell me if this makes sense to you guys. I feel that the revs drop faster after the "new" software - it seems I have to start the motion of letting the clutch up earlier to compensate. Could this be possible because of a software change?

I've had the car since new. Never even touched 4000 RPM during break-in. Oil changed at 1200, 7500, and 16000 (when the first yellow light came on), the car now has 19000. The car's life-time average in fuel consumption is 18.5 according to the computer, so I hardly get on this car at all. It has been burning 1 quart of 5w30 per 1000 miles since new. I can't imagine how much oil it will burn if I get on it all the time.

BTW, bad gas can be ruled out since I go to all different stations, and the same gas I put in my other car does not cause a rotten egg smell.

Any input much appreciated.
 

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bad MAF's were the culprits when i had this problem. They have a tendancy of not showin up on the OBD diagnostics!

i had my delaer change O2 senosr, CAM positioning sensors and even clean my fuel injectors!! Only replacing the MAFs solved my problems!

Stuteering, misfiring, strong smell from exhaust, engine tone changing, car wouldnt pull in high gears, car would stall ! Sometimes wouldnt start! Sometimes would start but go off after extensive stuttering!!!

These were the symptoms i had!

If the probelms still persisit, have them replcae the MAF connectors and cables!
 

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Discussion Starter #4
Thanks for the suggestion.

I brought this up with my SA. At first he was very willing to give the MAF a shot - he says sure I'll see if I've got one in stock and pop ONE in. Then I told me M5 has TWO. He was kind of skeptical and asked another guy. Yep it has two. With no fault code BMW will reject the claim for two of these things (~$1000). He'll have to get it pre-approved from the BMW rep.

I will keep you guys posted.

BTW, can the MAF go at anytime? My car only has 19k miles on it. No K&N, 100% bone stock. Also, what do you guys make of the fault code from the computer "cat conversion efficiency"?
 

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andye39s said:
Thanks for the suggestion.

I brought this up with my SA. At first he was very willing to give the MAF a shot - he says sure I'll see if I've got one in stock and pop ONE in. Then I told me M5 has TWO. He was kind of skeptical and asked another guy. Yep it has two. With no fault code BMW will reject the claim for two of these things (~$1000). He'll have to get it pre-approved from the BMW rep.

I will keep you guys posted.

BTW, can the MAF go at anytime? My car only has 19k miles on it. No K&N, 100% bone stock. Also, what do you guys make of the fault code from the computer "cat conversion efficiency"?
Find a new dealership. These guys are just parts changers.

BMW will not preapprove it without a reason! Sounds like they don't have the smarts to figure it out without the computer telling them. Read DavidS' post- print it- hand it to them

They should try the new mafs, if it works great- mafs were bad- fill out the paperwork. If it doesn't, take them back out and put them on the shelf for the next time they need them!
 

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Andye39,

It is obvious you have a not-so-M5-experienced SA. He can very well be a good SA anyway, but it won´t help you in this matter. Ard has a good point, you may want to try another dealership.

If think that if you perform the rather uncomplicated MAF test yourself, you will have a figure indicating how the MAFs perform. Then you can give the SA some hard facts to relay to the BMW area rep, and get appropriate action decisions from BMW.

It is a sad fact that the BMW diagnostics for MAF are very ineffective. The MAFs have to be more or less totally broken to get an error message.

The reason why the BMW test does not work well is that it tests the MAFs with the car standing still, no load on the enigine at 2000 RPM. The method I posted tests the MAF at full load at 7000 RPM on the road. The air-flow through the MAFs (and correspondingly the measurement accuracy) is about 50 times bigger on the road than when standing still.

David
 

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andye39s said:
Also, what do you guys make of the fault code from the computer "cat conversion efficiency"?
This is a fault code (178 and 179 depending on which side IIRC). It means the preset limits between the front O2 sensor ( which is part of the measuring/feedback loop) and the rear O2 sensor (which merely compares the front O2 value to the rear) are being exceeded.
Sulphur smell is usually raw gas being burned by the cats. So bad MAFS could certainly be a viable culprit. Surprising your gas mileage is good, as it sounds like the car is running rich. Have they done simple diagnosis like pulling plugs and reading them?
Also agree, consider another dealership. Check with Fast5 (Robert), he works at a NJ dealership, and another member MannyM5 also works at one. You might want to PM them and see if they are near you.
Good luck and keep us posted.
Regards,
Jerry
 

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Gsfent is right. It is well known on this board that "cat conversion efficiency" on an M5 indicates a MAF problem with very high probability. Obviously BMW still hasn´t updated the diagnostic system software so it suggests MAF replacement before catalytic converter replacement on M5s.

Do a few searches on MAF and cat (inkluding various synonyms) and you will come up with many posts about this.

David
 

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Discussion Starter #9
OK I got both MAFs replaced. My car is back!!! No more stumbling in low RPMs, no more rotten egg smell (but still a little rich smelling, I guess it's the nature of this car). Car pulled nicely, even on a hot humid day.

My SA was somewhat hestitant when I *told* him to replace the MAFs, so I printed out and showed him this thread. I guess it was when you guys suggested that I go to another dealship that prompted him to replace them for me. He wouldn't want to lose me since I always take care of his survey. It definitely pays to build a good relationship with your SA. They know exactly what you say and how you rate them in the survey.

Thanks guys!!

Oh BTW, the power issue is fixed, but now there's a moaning kind of sound coming from the driver side in the front. It changes pitch with RPM. At faster speeds (~80mph) the sounds kind of drones in my ears! I suspect it's from the air intake somewhere. I checked the MAFs and they are installed correctly (air flow direction). Any ideas?

I'll bring it back in to check for this noise in 2 weeks. Next time I'll take the 325 convertible loaner instead of the X3!
 

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Glad it worked out, Andy!

The sound you describe could be many things. (belts, generator, water-pump, power-steering-pump, A/C, a timing chain). Open the bonnet (hood) and listen where it comes from.

Now, may I ask a favour of you, now that you have brand new MAFs on?
Please have a look at the MAF testing thread I posted earlier in this thread, and run a DIY MAF test and post the numbers in the MAF thread.

We need this data from cars with new MAFs to help diagnose other MAF and fuel injector problems.

Best Regs,

David
 

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andye39s said:
OK I got both MAFs replaced. My car is back!!! No more stumbling in low RPMs, no more rotten egg smell (but still a little rich smelling, I guess it's the nature of this car). Car pulled nicely, even on a hot humid day.

My SA was somewhat hestitant when I *told* him to replace the MAFs, so I printed out and showed him this thread. I guess it was when you guys suggested that I go to another dealship that prompted him to replace them for me. He wouldn't want to lose me since I always take care of his survey. It definitely pays to build a good relationship with your SA. They know exactly what you say and how you rate them in the survey.

Thanks guys!!

Oh BTW, the power issue is fixed, but now there's a moaning kind of sound coming from the driver side in the front. It changes pitch with RPM. At faster speeds (~80mph) the sounds kind of drones in my ears! I suspect it's from the air intake somewhere. I checked the MAFs and they are installed correctly (air flow direction). Any ideas?

I'll bring it back in to check for this noise in 2 weeks. Next time I'll take the 325 convertible loaner instead of the X3!
Glad you got it taken car of. Must feel like you have a whole new car!!
Noise can be a lot of things as mentioned. Confirm it is road speed related, not engine speed related. If so, then unlikely belts, as that noise should be at same engine speed.
Since the monkey lads were under your hood replacing MAFS, look for a loose clamp or other connection somewhere. Could be a hose or attachment was not properly seated. At speed that could be air "whistling" through an opening.
Regards,
Jerry
 
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