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So i took my 99 M5 with 112kms (65mls) to a local BMW workshop due to a hesitation under load when car is at operating temp, seems to be really noticable under 2000rpm. They diagnose the problem to be the drivers side MAF, and want about $900 nz dollars each!!
I manage to import a pair of OEM bosch units for about half the price- and have just installed them.
Have driven about 25km (10miles) quite hard with no improvement, i did disconnect the battery whilst doing the install (took about 15min).
Should i have noticed an instant improvement or does the computer need alot more kms to readapt-? Like i said no improvement, I have only had the car about a month, and it could have been running like this for some time before hand, exhaust is black and can see specks of carbon on bumper after a few days when i dont wash it.
 

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Don't need to disconect the battery to change MAFS...

do you still have the old MAFS?

If so, put them back in and run the MAFS test post # 11, then again with the new ones (or just run the new instaled ones first to see what you have);

http://www.m5board.com/vbulletin/showthread.php?t=1898

...and by the way, that's test - - 4) Current fuel consumption in liters per 100 kilometers and in liters per hour. - - -press it twice to get the liters per hour, this what you want -optimum is 140ish liters per hour - - best is Wide Open Throttle (WOT) redline in 2nd/3rd gear...


...it does take some time to adjust to new MAFS, but the test helps to show the raw/major issues.


also the following thread is good for anything else you can dream of about MAFS;

http://www.m5board.com/vbulletin/showthread.php?t=54788<!-- / message --><!-- edit note -->
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I don't think decisions can be made on the experience of such a short adjustment time.

I'm not an expert in engine management systems but every time I have had things replaced (CPS, MAF, fuel pump) it has shown instant improvement but has optimised over the next 100, sometimes 200 miles.
 
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I think maybe the computer needs a bit more time to adjust, if no improvement after that look else where for the problem, maybe o2 sensors.

As for the black specks on the rear bumper no bigggy, I saw a brand new M3 with the same. From the questions I have asked here and what I have read the engine does not like to be babed and needs to be driven hard to reduce this. BMW like their high revving motors (and so do we) and the optimal operating rpm is higher than most people think, so when below this, that is when the carbon is produced.
 

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I had my car serviced at the local dealer here and the computer diagonsed that there was a fault with the fuel/air mix, which they pointed out to be either the O2 sensors or the MAF's.

Turns out all they did was reflash the ECU to the latest software and the problem fixed itself. I didn't really notice any difference except the engine runs a little hotter now, almost exactly at 95C where as before it was closer to 85.

Not sure if this is of any help....
 

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I think maybe the computer needs a bit more time to adjust.
Yes, and there is no one number that you are looking for. All depends on your driving style, and start-stop cycles. I wouldn't worry until you have passed 200 miles, but that too is a guess.

As for the black specks on the rear bumper no bigggy, I saw a brand new M3 with the same.
... of NO consequence. The dealer could have just been letting a potential customer hear the engine (and, reving it in the lot), and it may have never been off the lot (and, it probably never got properly warmed up). Also, new engines need time to adjust to their new owners.

From the questions I have asked here and what I have read the engine does not like to be babed and needs to be driven hard to reduce this. BMW like their high revving motors (and so do we) and the optimal operating rpm is higher than most people think, so when below this, that is when the carbon is produced.
YES, YES, YES ... I believe carbon is always produced, even if small quanities. It makes a difference if you drive mostly fast or mostly slow. Wind motion around the rear of the car plays a part, as well.
 

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after I changed mine out (they'd gotten fouled enough to give me an SES/ limp mode on full throttle) I saw pretty good gains after give or take 300 miles. About the same as new plugs. Both done around 68k miles.

- Tim
 

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having had the same symptoms, i would have made the same diagnosis - need new MAFs. (perhaps you need both sides)

from what Ive read, our cars need these replaced every 40 - 50K miles.

if you try swapping the MAF to the other side and dont recog a difference, then something else is going on.

generally low RPM issues are timing and airflow issues, at higher rpms, it can be fuel-related.

good luck!!
 
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