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Troubleshooting power loss under full throttle & limp mode?

8K views 22 replies 13 participants last post by  Tall Person 
#1 ·
Hey guys:

I'm hoping you guys can diagnose my problem.

My car:
2000 MY M5
36000 hard rally miles
Dinan Stage 1 Chip
No other engine mods.

Summer 2004: Driver and 1 passenger with full trunk. Sport Mode, red-lined engine in 4th gear and experienced sudden power loss. It felt as if half the cylinders had shut down. I drove the car at moderate speed (assuming I was in Limp Mode) until the engine power was restored (electronic management saving me). BMW New York said the engine was fine.

Check engine light came on yesterday after routine service at BMW Manhattan. They said "it was probably nothing" but to bring it back in just in case.

Today: 4 passengers and some luggage in regular mode. Full throttle in 4th Gear and had similar power loss at 4500rpm. Engine seemed to reset after 1 hour of moderate driving.

Tried full throttle again two hours later and problem repeated itself.

Waited another hour (after light driving) and attempted full throttle in 2nd gear. Engine power was cut in half at 2800 rpm.

I drove home.

Am taking car to BMW Manhattan Monday.

Any ideas for what problem is?

Best,
Alex
 
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#2 ·
The two things that come to mind are the thermostat or MAF's. Have you changed your plugs yet? Hopefully it's not the carbon issue. Not sure of those symptoms...maybe do a search.

Funny, because I just experienced my first limp mode in the M. I was cruising just under red line in second gear for maybe 30 seconds and bam, limp. Shut her off, turned her on and all was fine again.

PS: I just wanted to say that video of you in Italy escorted by a policeman was fantastic! Way to go.
 
#3 ·
cam position sensors (cps) or fuel issue... my guess.

Did you notice a funny 'blatty' sound from the exhaust?

Anyway, see what codes the dealer reports and post them here before agreeing to big $$$.

Ditto on the video- did you ever get back to him via email? does he know he is 'famous'? :)
 
#6 ·
#8 ·
DavidS said:
I agree with the above:

Either a camshaft position sensor (CPS)

or

the crankshaft position sensor (also called CPS)

or

bad MAFs. (do a MAF test to rule that out: http://www.m5board.com/vbulletin/showthread.php?t=54788 )

Or a combination of the above.

David
Hey David-

What is the 'process' associated with the MAFs triggering a 'limp home mode'?

I always viewed the MAF issue as a slow degradation issue, untill they were so bad they trigger a fault code- how does a bad maf that still works creat a transient limp home? Does the AFR ge so out of whack (lean?) that as a protection the DME limps? What non-MAF code/error would one expect to see, if indeed one is set?

Thanks

Adam
 
#9 ·
There are posts about lots of recurring limp-home-mode instances cured by a new set of MAFs or a new CPS.

If the MAFs are really bad mixture will be lean enough to force the engine into limp-home-mode.

The crankshaft sensor is very sensitive to being correctly aligned at installation. If it is not installed correctly it will not be reliable. This causes misfires, or crankshaft7camshaft syncronisation fault-codes. Both can give power losses and/or fault codes with the SES light on.

David
 
#10 ·
DavidS said:
There are posts about lots of recurring limp-home-mode instances cured by a new set of MAFs or a new CPS.

If the MAFs are really bad mixture will be lean enough to force the engine into limp-home-mode.
Oh, I know- I was just wondering the mechanism for it. It doesn't set a 'bad MAF' code, so I was curious as to what it would masquerade as....

A
 
#12 ·
Beamer_usa said:
Same thing happened to me, ended up being CPS, changed under CPO, all is well now:)
Was it a camshaft sensor or the crankshaft sensor?

David
 
#15 · (Edited)
Sweet we have our own "celebrity" :thumbsup:
 
#16 ·
Not YET confirmed for Gumball..

Hey guys:

I got the MAFS replaced and am still considering doing the Gumball. I'll know within a few days.

Thanks for all the help and support.

Best,
Alex
_____________________
 
#22 ·
Alex,

I think you might very well have a crankshaft sensor problem still, so IMHO you ought to bring a crankshaft sensor (small and not very expensive part) and a few shims (pennies) for it with you. Also bring a measurement caliper to be able to adjust the sensor. A cheap one will do fine.

David
 
#23 ·
Cutting out under hard acceleration - Light at the end of the tunnel!

I have a problem with a friends 2000 M5, which after reading some of the posts on this forum, I suspect may be linked to MAF or CPS sensors.
It has been into a BMW dealer who hooked it up to the computer to reveal no fault codes stored. The car sometimes does not seem to have the power it should have, but sometimes what happens is that when accelerating hard in 4th gear, the engine cuts out at about 4500rpm and reverts to limp home mode. No lights are shown on the dashboard, but you can then only drive using up to 2500rpm. Turning the ignition off and restarting soon after and the car is back to normal. This does not seem to happen in any other gear. The car recently failed the MOT on high emissions, but nothing was flagged up on the computer at BMW. Subsequently, a local MOT garage removed and cleaned the oxygen sensors in the exhaust and it then passed the MOT. However, the cutting out problem was still there.

After seeing some posts regarding the MAF sensors, we tried an experiment and disconnected them. The car runs spot on, does not cut out and the performance is amazing, as it should be!This seems to be the root of the problem.

Next stage is to check the MAF sensors, clean if possible, otherwise replace them. Thanks for the info from the forum guys, I think we have got the solution! :checkeredflag: hiha :checkeredflag:
Cheers,
Raoul.
 
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