Hot, humid M5 is nearly dead - The Unofficial BMW M5 Messageboard (m5board.com)

Timray · 6th July 2005, 22:42

This post is on behalf of Paul, owner from new of an E39 M5 in the UK:

"In hot, humid weather my engine is hesitant and nearly cuts out - particularly on the overrun (i.e. when no throttle is applied, for example after braking). The car is fine when cold. The dealer, Bowker of Accrington, can find no fault; unfortunately I took it in on a cool day. Idle speed is 500rpm and the car is three years old with 33,000 miles."

Any ideas?

Regards

Tim

DavidS · 7th July 2005, 00:40

1. Test the MAFs yourself:

How to test the MAFs yourself and How MAFs work

2. Did the dealer check the exhaust gases? If so, what were Lambda value and NOx level?

3. The idle speed is way low. How did you measure it? It should be about 630 RPM.

David

Timray · 7th July 2005, 00:51

Excellent information; many thanks. I'll ask about the Lambda value and NOx level.

Best, Tim

gsfent · 7th July 2005, 01:03

Quote:

Originally Posted by Timray

Excellent information; many thanks. I'll ask about the Lambda value and NOx level.

Best, Tim

Also check for vacuum leak.
Regards,
Jerry

DavidS · 7th July 2005, 01:09

Does "Dealer could find no fault" mean they just plugged the computer in, and it could find no fault-codes stored, or does it mean they actually did what they should:

1. Checked fuel pressure and fuel flow (and did it by the book TIS RA 1331 & TIS RA 1331029)
2. ran diagnostics of the MAFs
3. ran diagnostics of the Idlespeed regulator
4. look at the spark-plugs
5. check compression

If not, go motivate them.

This is most likely either fuel pressure or MAFs or both. Or indeed a vacuum leak as Gsfent pointed out. A vacuum leak would give the same symptoms as a contaminated MAF.

David

Timray · 7th July 2005, 01:29

Quote:

Originally Posted by DavidS

Does "Dealer could find no fault" mean they just plugged the computer in, and it could find no fault-codes stored...?

Paul quotes the dealer as reporting "there is no fault stored", but also says the dealer "downloaded new software and adjusted the throttle bodies". According to Paul, the dealer said it was not possible to raise the idle speed.

David & Jerry: again, many thanks. Paul is an M5 owner who has yet to discover the Internet - he will be startled by the speed and quality of these replies.

DavidS · 7th July 2005, 01:40

Quote:

Originally Posted by Timray

Paul quotes the dealer as reporting "there is no fault stored", but also says the dealer "downloaded new software and adjusted the throttle bodies". According to Paul, the dealer said it was not possible to raise the idle speed.

David & Jerry: again, many thanks. Paul is an M5 owner who has yet to discover the Internet - he will be startled by the speed and quality of these replies.

About the dealer: Thought so...

Tell Paul hi from me, and encourage him to either go back and in a friendly manner educate his SA, or go to someplace where the brain is still used as a diagnostic tool.

a. The trottle bodies have nothing at all to do with the idle speed. Those are completely shut at idle. The air comes from the idle-speed air valve.
(but if the trottles were leaking air when supposed to be shut, it would affect the idle. It is not impossible as the source of the problem, but so unlikely compared to the other possibilities it should be checked after the rest has been ruled-out)

b. Did they charge him for the software upgrade? I fail to see the point of that without a good indication.

How did the problem evolve: did it appear suddenly or gradually?

David