ok, so ive been reading on the m5board about MAFs since i have always suspected mine is bad. Its the original one and my car has 90k miles on it. I decided to go mess around with my car the other day to see if i could find anything else out. The car has been running slow for a while.

I read about running test number 4 on the gauge cluster that shows how much fuel is being put into the motor through its rev range. Well, i read that an m5 is supposed to have 140 L/H of fuel flow at redline. I figured ok, ill try that on my 540 and see what the numbers are. i knew they wouldnt be 140 L/H but as long as it read the highest amount at or near redline, i should be ok.

I got in the car (fully warmed up) and went to test number 4 and have it read in L/H. I floor the car in 2nd gear and the fuel flow rises. As it got to 4800rpm it hits a max of 80 L/H and then after 4800rpm, it started going back down to 70 or even 60 L/H. I shift into 3rd and keep it WOT. The Fuel flow from 4000rpm to 6000rpm never read above 50 L/H. And i know that the car felt slow.

I pulled over in a parking lot, turned the car off, popped the hood and unplugged the MAF. I cranked the car up again and immediately, the traction control light came on. The car started and i reved it a few times to about 3500rpm and it reved fine. I turned the car off, plugged the MAF connector back in, shut the hood and started the car. The traction control light was still on which i thought was weird.

I took it out for a test drive like this to see what it would do. I pull out onto the road and floor it in 1st gear. The right rear tire started spinning and the car was banging off rev limiter. I shifted hard into 2nd and it spun both tires pretty good. It ripped towards redline so i shift into 3rd gear and it pulled HARD toward redline again. I could not believe it. The car was SOOO much faster. I didnt know the car could be this fast.

For whatever reason, i didnt check the fuel flow that time so i dont know what it would have read.

I pulled into another parking lot and turned the car off. I made a quick phone call and 3 mintues later i restarted the car. The traction control light was off and the car was 'normal' again.

I get out onto the road and floor it in 1st gear. It does nothing but accelerate like it always has. It did NOT spin the tires. I shifted hard into 2nd and the car did not spin the tires in 2nd. I shift hard into 3rd and the car just accelerates slowly like it always has.

Anyway, im pretty sure its the MAF now that is cauing my car to run slow.

I bought the VW MAF for 71 dollars off of the link in the thread on M5board.com and its arriving tomorrow. Im going to swap them out and see what happens.

Anyone else played around with this?

Does anyone know what the max fuel flow in L/H would be for an e39 540i?

Sounds more like a traction control issue than MAF.
Try driving w/ trac control off.

It's more than likely not the MAF, since you never tested the car while the MAF was unplugged.

Trac control prevents tire spin and if it detects it, limits throttle, applies brakes, etc, etc.
Turn off trac - repeat test. :D

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I have a feeling the OP knows the difference between traction control bogging the car and the car not accelerating like it should.

To answer the OP's question - I have had very similar results.

I took the car into the shop to have the vent valve cover replaced last August, and when I was driving home, it felt like it was driving off 6 cylinders - absolutely NO acceleration. A day later the CEL came on, so back to the shop. Turns out it was a bad MAF sensor.

The first drive after I got the MAF sensor replaced was an amazing one. The car felt like it never had before - just AWESOME acceleration. The MAF sensor is most definitely a cause of poor acceleration.

yeah, im pretty sure i know the difference between when traction control is kicking in and when it is not. :D Im very well versed in cars and how to work on them better than most techs at bmw.

Im 99.999% sure my maf is bad.

I just wanted to know if anyone knows the max fuel flow i should see out of my M62. As of now, im getting only ~50 liters per hour of flow at redline while i get 80 liters per hour sometimes and the car feels faster.

and,

Id like to know what the computer is doing to give me my acceleration back when i unplugged the MAF. Its like it goes into a safe mode or uses preset values to make the car run. Maybe those preset values are better than what my MAF is inputing into the ecu and causing the car to run better. Who knows, im just guessing right now.

Cant wait to find out if its a bad maf or not.

so can you drive the car with the MAF unplugged? or did u unplug it an dplug it back and took it for a spincause im having similar problem

Not to be negitive or anything... but I asked the guy that figured out you can use the VW MAF for the M5, and he said you CANNOT use it in the 540. He said the 540 MAF is different from the M5 ones. If it works, tell us because I have also suspected that my MAF is not 100% either. Good Luck

I also suspect my MAF for poor performance and hesitation. Keep us posted. I would have disconnected my MAF except I am not sure where it is on a Dinan installed SC.

Where can I find the info on all the different OBC tests you can do on the 540i?

I unplugged the connector to the MAF
Started the car.
Reved up to ~3500rpm maybe twice
turned car off
plugged MAF connector back in
Started car
took for a test drive and it was much faster.

Not to be negitive or anything... but I asked the guy that figured out you can use the VW MAF for the M5, and he said you CANNOT use it in the 540. He said the 540 MAF is different from the M5 ones. If it works, tell us because I have also suspected that my MAF is not 100% either. Good Luck

Yeah, thats what i would have thought too. Ive spoken to 2 different people that have done this in their 540s and it worked. I could have sworn ours was different but i figured for the 70 bucks it might be worth a try. If it doesnt work, i will resell the thing and get most of my money back if not all. I was about to buy the bmw specific one for 300 but figured id try this out first. If it doesnt work, ill try that crc MAF cleaner like i probably should have done in the first place.

Here is a post i could find off the m5board discussion. Just read it, tell me what you think....
http://www.m5board.com/vbulletin/showpost.php?p=809815&postcount=66

I tried the CRC cleaner. I didn't really feel any gains. My MAF didn't look dirty, but it doesn't mean that it is not old and tired (it has 118,xxx miles). If the VW MAF works then I will be out to get one to try it on my car. I'll keep my fingers crossed.

I talked to Dinan and they told me that if I disconnect the MAF, that the car would not run. Any help?

I unplugged the connector to the MAF
Started the car.
Reved up to ~3500rpm maybe twice
turned car off
plugged MAF connector back in
Started car
took for a test drive and it was much faster.

Not to be negitive or anything... but I asked the guy that figured out you can use the VW MAF for the M5, and he said you CANNOT use it in the 540. He said the 540 MAF is different from the M5 ones. If it works, tell us because I have also suspected that my MAF is not 100% either. Good Luck

Yeah, thats what i would have thought too. Ive spoken to 2 different people that have done this in their 540s and it worked. I could have sworn ours was different but i figured for the 70 bucks it might be worth a try. If it doesnt work, i will resell the thing and get most of my money back if not all. I was about to buy the bmw specific one for 300 but figured id try this out first. If it doesnt work, ill try that crc MAF cleaner like i probably should have done in the first place.

Here is a post i could find off the m5board discussion. Just read it, tell me what you think....
http://www.m5board.com/vbulletin/showpost.php?p=809815&postcount=66

Where can I find the info on all the different OBC tests you can do on the 540i?

click this-
http://www.m5board.com/vbulletin/showpost.php?p=14749&postcount=11

I also suspect my MAF for poor performance and hesitation. Keep us posted. I would have disconnected my MAF except I am not sure where it is on a Dinan installed SC.

I would be scared to risk that with a 540 with forced induction. I always thought that my car would die too when I unplugged the sensor. I guess they change something when you install an SC. Im pretty sure your MAF is just lower in the engine bay where the intake goes down into the bumper. I could be wrong but it looks the same as it did before so you will just have to look around.

I would be scared to risk that with a 540 with forced induction. I always thought that my car would die too when I unplugged the sensor. I guess they change something when you install an SC. Im pretty sure your MAF is just lower in the engine bay where the intake goes down into the bumper. I could be wrong but it looks the same as it did before so you will just have to look around.

That link gives me hope for us. We both have pre vanos cars.. I know the 540's with vanos the MAF's are different. So I guess we (by we, I mean you, and me waiting to hear from you) will have to see what happens with the VW MAF's.

The reason the car would run without the MAF plugged in is because it is stored in the cars memory. I am not exactly sure... but if you unplugged MAF, then unplugged the battery to clear the cars brain. Then I do not believe the car would start. I am not 100% on that though.

The reason the car would run without the MAF plugged in is because it is stored in the cars memory. I am not exactly sure... but if you unplugged MAF, then unplugged the battery to clear the cars brain. Then I do not believe the car would start. I am not 100% on that though.

Might be on to something here. The DME stores adaptations for a bunch of stuff, one of which may be average MAF readings for specific RPM ranges. When you unplug the MAF now there are no readings so the DME uses it's stored values, and perhaps loads the new null values into the memory - clearing out the stored values you had before. When you start the car again with the MAF plugged in, the values have been cleared and not able to adapt yet so they just use a default set and that's where the extra power comes from. This is all just speculation, of course.

ill let you guys know what happens tomorrow night in this thread. Ill take pictures as well of what Im doing so you/we can see the differences and whatnot.

I just did the same test on my 5 and got a peak of about 79 L/H. My car has about 77k miles on the original MAF.

WOW! Lots of misinformation and speculation in this thread.

It is sad to me, that everyone these days runs straight to the MAF when they think their car isnt running right. Or in this case, isnt a tire burning M5.

My car has 152k on it, and the original MAF, and there isnt a damn thing wrong with it. If anything it could use a gentle cleaning.

I suppose you might get a VW or Land Rover or whatever MAF to hook up in place of your original, but unless it is the exact same part number, and you had confirmation from Bosch design engineers of this, you may want to reconsider buying the genuine part. Thats all I will say on that, let me get to the other shit.

The MAF does NOT measure fuel flow. Period. It measures the amount of air coming into the engine. This data is provided to the DME in Liters per hour format. The DME uses this information for a few different things, and yes it can run without having the bastard plugged in.

Unplugging the MAF will NOT give your car any more power. What happened in this case is John unplugged the MAF, started the car, got an instant stability control fault and shut down. As you may have seen under your hood, there are two throttle bodies on these cars, and only one is direct linked to the gas pedal itself. The other is controlled by the stability control which operates off values it recieves from DME inputs- one of which is the MAF signal. Others would be wheelspeed, engine rpm, throttle position, etc etc. If he had left the MAF unplugged I doubt the car would have driven very well at all, IF it would even move at all under load.
The reason the light stayed on even after reconnecting the MAF is it was still letting the driver know that there was a recent major fault in the stability control system. I bet if I were to scan the cars DME now it would give a MAF fault with an occurance of 1, no longer present, sporadic.
Why did it seem to run so much better you might ask? Mookish awnsered that question above- when the stability control lamp comes on and does not go out, and you have not disabled the system, there is a fault and the system is INACTIVE. Here is a test for you, go out and drive your car for a week and never turn the stability control off. Then leave it off for a week, and see which week was more fun. I have noticed myself that disabling it wakes the car up a good bit however its not the engine performance that is hampered by the ASC it is simply the cars way of trying to save the driver some wear and tear on the driveline and tires. (and the insurance and legal fees in my case) This is along the same reasoning that led BMW to produce the car with a fluid restrictor or delay valve in the hydraulic clutch system- the best way I can put it to you is to create the "ultimate driving machine" they seriously OVERengineered the suspension, gave it more than enough power and then added standard equipment to the car that disconnected the driver from the actual feel of the car. The end result is obvious, the cars were quite popular with their owners but are often misunderstood.

When you spin "tires" in a e39 540i6, you spin the right rear tire and thats it. Period. Theres no way you spin just the right rear at launch and then spin both when you shift into 2nd. Not possible. I IS possible to spin the left rear, but only in reverse, and the right rear becomes the dead side then.

"yeah, im pretty sure i know the difference between when traction control is kicking in and when it is not. :D Im very well versed in cars and how to work on them better than most techs at bmw."

HA! Thats definitely the quote of the week. Especially since you go on and on about how your MAF is measuring FUEL flow. Dont quit your day job.

i disconnet my MAF and my 540 won't run

WOW! Lots of misinformation and speculation in this thread.

It is sad to me, that everyone these days runs straight to the MAF when they think their car isnt running right. Or in this case, isnt a tire burning M5.

My car has 152k on it, and the original MAF, and there isnt a damn thing wrong with it. If anything it could use a gentle cleaning.

I suppose you might get a VW or Land Rover or whatever MAF to hook up in place of your original, but unless it is the exact same part number, and you had confirmation from Bosch design engineers of this, you may want to reconsider buying the genuine part. Thats all I will say on that, let me get to the other shit.

The MAF does NOT measure fuel flow. Period. It measures the amount of air coming into the engine. This data is provided to the DME in Liters per hour format. The DME uses this information for a few different things, and yes it can run without having the bastard plugged in.

Unplugging the MAF will NOT give your car any more power. What happened in this case is John unplugged the MAF, started the car, got an instant stability control fault and shut down. As you may have seen under your hood, there are two throttle bodies on these cars, and only one is direct linked to the gas pedal itself. The other is controlled by the stability control which operates off values it recieves from DME inputs- one of which is the MAF signal. Others would be wheelspeed, engine rpm, throttle position, etc etc. If he had left the MAF unplugged I doubt the car would have driven very well at all, IF it would even move at all under load.
The reason the light stayed on even after reconnecting the MAF is it was still letting the driver know that there was a recent major fault in the stability control system. I bet if I were to scan the cars DME now it would give a MAF fault with an occurance of 1, no longer present, sporadic.
Why did it seem to run so much better you might ask? Mookish awnsered that question above- when the stability control lamp comes on and does not go out, and you have not disabled the system, there is a fault and the system is INACTIVE. Here is a test for you, go out and drive your car for a week and never turn the stability control off. Then leave it off for a week, and see which week was more fun. I have noticed myself that disabling it wakes the car up a good bit however its not the engine performance that is hampered by the ASC it is simply the cars way of trying to save the driver some wear and tear on the driveline and tires. (and the insurance and legal fees in my case) This is along the same reasoning that led BMW to produce the car with a fluid restrictor or delay valve in the hydraulic clutch system- the best way I can put it to you is to create the "ultimate driving machine" they seriously OVERengineered the suspension, gave it more than enough power and then added standard equipment to the car that disconnected the driver from the actual feel of the car. The end result is obvious, the cars were quite popular with their owners but are often misunderstood.

When you spin "tires" in a e39 540i6, you spin the right rear tire and thats it. Period. Theres no way you spin just the right rear at launch and then spin both when you shift into 2nd. Not possible. I IS possible to spin the left rear, but only in reverse, and the right rear becomes the dead side then.

"yeah, im pretty sure i know the difference between when traction control is kicking in and when it is not. :D Im very well versed in cars and how to work on them better than most techs at bmw."

HA! Thats definitely the quote of the week. Especially since you go on and on about how your MAF is measuring FUEL flow. Dont quit your day job.

thanks for posting. I too believe that everyone runs to the MAF when the car isnt running right. Im the one usually telling people its NOT the MAF that is causing the problems. For my car, the MAF is the LAST thing that I am checking to find my lost power. The rest of the car is in perfect working order. Everything else is either new or working properly. Today i lost to an '01 530i driven by a soccer mom on the way to work today.

First off, for the past year, every time i get in my car i do the following procedure.

Shut door,
turn on car,
push ASC button (meaning traction control disabled)
Put on seatbelt
drive off.

I never have the traction control on so i am assuming that it should have 'learned' by now that i dont want that on.

I guess all the m5 owners are just as stupid as I am. I know that the MAF does NOT measure fuel flow but there is a direct relation between the MAF and fuel flow. If the MAF is acting up and sending the DME inaccurate or lesser air flow readings, then shouldnt the DME match that air flow reading with the proper amount of fuel? Please explain to me why every M5 owner that has replaced the MAF has gotten higher fuel flow readings than before when the car was lacking power. All they did was change the MAF, they didnt do one different thing than swap 2 sensors out.

An open differential will spin both tires if both have equal traction. I have a picture to prove that of a huge burnout i did when my tires were shot. Plus i have video of my last 540i leaving 2 black tire marks 3 feet long when i shifted hard from 1st to 2nd.

I do NOT have an LSD but why does my car do this? This is in 2nd gear!
http://carpron.com/multisite/d/81261-2/DSC_0838.JPG

Im really not expecting this to work but for 70 bucks, im going to give it a try since no one else would try it.

also, im going to mess around with the traction control ideas as well. Im not doubting that the traction control is the issue, and it probably will be the culprit but it just seems odd that the traction control would hinder the cars performance sooo much even when the traction control is switched off. Sometimes, im dead even with my roommates 99 m3 with intake,exhaust, software upgrade. Sometimes i lose to a pontiac gran prix (non gtp) or cadillac escalades, or 530s, fc rx7 NON turbos.... i just dont get it.

here is some reading for everyone as well to make their own opinions.

http://www.m5board.com/vbulletin/showthread.php?t=54788&highlight=MAF+test
http://www.m5board.com/vbulletin/showthread.php?t=73578&highlight=vw

so for my lunch break today, i said screw food.. im going to mess with my car instead.

I got in the car drove it down the street watching my fuel flow in liters per hour. At redline in 3rd gear it was reading 54.x L/H.

pulled over, turned car off, unplugged the traction control connector. Tried the same thing- still read 55-56 L/H. The traction control worked exactly the same with the connector unplugged. It did not give me a fault code and the trac light stayed off until i pushed the button to turn the system off.

I then unplugged the cruise control plug to hopefully make it throw a fault code and keep TRAC all the way off. I checked my fuel flow at 3rd gear redline this time and it read 79 L/H.

This make me think that its not the MAF like i always thought but now im dumbfounded by this traction control BS.

Seems like the car ran ok with both trac and cruise unplugged but it wouldnt spin the tires or bark 2nd like it did the other day (probably the clutch). The only thing i have done is reset the battery today. In my last 98 black 540i bone stock with the identical wheels and tires, i could be rolling in 1st gear and punch it and it would spin the right rear and hit the rev limiter. My silver car will not do this at all.

Sometimes ill be in 4th gear on the highway and floor it to get around someone and the car does not accelerate at all. There is no difference in me giving it 10% throttle or 100% throttle. It accelerates the same.... Or if i go around a turn hard, i have the same or 0 power until the car isnt feeling a G load, i sit there waiting for it to start going, then it seems like it flips a switch and starts pulling again. I dont know, im getting frustrated because this is so annoying.

so for my lunch break today, i said screw food.. im going to mess with my car instead.

I got in the car drove it down the street watching my fuel flow in liters per hour. At redline in 3rd gear it was reading 54.x L/H.

pulled over, turned car off, unplugged the traction control connector. Tried the same thing- still read 55-56 L/H. The traction control worked exactly the same with the connector unplugged. It did not give me a fault code and the trac light stayed off until i pushed the button to turn the system off.

I then unplugged the cruise control plug to hopefully make it throw a fault code and keep TRAC all the way off. I checked my fuel flow at 3rd gear redline this time and it read 79 L/H.

This make me think that its not the MAF like i always thought but now im dumbfounded by this traction control BS.

Seems like the car ran ok with both trac and cruise unplugged but it wouldnt spin the tires or bark 2nd like it did the other day (probably the clutch). The only thing i have done is reset the battery today. In my last 98 black 540i bone stock with the identical wheels and tires, i could be rolling in 1st gear and punch it and it would spin the right rear and hit the rev limiter. My silver car will not do this at all.

Sometimes ill be in 4th gear on the highway and floor it to get around someone and the car does not accelerate at all. There is no difference in me giving it 10% throttle or 100% throttle. It accelerates the same.... Or if i go around a turn hard, i have the same or 0 power until the car isnt feeling a G load, i sit there waiting for it to start going, then it seems like it flips a switch and starts pulling again. I dont know, im getting frustrated because this is so annoying.


When was the last time you replaced your fuel filter? Before I replaced my fuel filter the second time (it was about three years old), my car would not pull hard and eventually it wouldn't let me rev past 4000 rpm. It would just pull back as if I was gearing down when I got to 4000 rpm.

My car feels a lot quicker since I replaced mine and that would explain your fluctuating fuel flow. I don't know how often BMW recommends that you replace the fuel filter but from now on I will be replacing mine every 12-18 months. I can only imagine the stress I was putting on my fuel pump by running the car with that clogged filter.

im glad you asked that. I actually have one on the way along with motor mounts, tranny mounts, and oil filter housing mounts coming from bmaparts.com

I am on the original one with 90k miles on the clock. I figured it would be completely bad but EVERY bmw tech and anybody i talk to about it says, NO its not the fuel filter. Watch that be the culprit.

Just curious....

is your car one of those cars thats just... 100000 times faster when its cool outside?

a 10 degree outside difference makes my car SO much quicker - none of my other cars have been like this.

Just curious....

is your car one of those cars thats just... 100000 times faster when its cool outside?

a 10 degree outside difference makes my car SO much quicker - none of my other cars have been like this.

Most of my past cars have actually been like this, I think it just has to do with the performance tuning of the DME. A higher output performance engine like the BMW series motors is going to be more affected by ambient temperatures than say a GM pickup truck with a more conservative engine tune. There are other factors too of course, but I think it just comes with the territory. The DME sees high tempertures and pulls back timing to keep everything running well.

Correct ambient air temp will affect performance due to timing changes on just about any car. I used to have a Supercharged FWD Pontiac that was a BEAST on cold winter mornings and disquised itself as a n/a motor on summer afternoons.
Now compared to BMW programming the old Pontiac is childs play, however the principal is the same.

JOHN have you replaced the cats? I would definitely suggest throwing a fuel filter at is before a MAF at any price.

Side note: I just replaced a motor mount on my car yesterday, if yours is as bad as mine was you want to check to be sure the fan isnt hitting the upper radiator hose sometimes.

I also suspect my MAF for poor performance and hesitation. Keep us posted. I would have disconnected my MAF except I am not sure where it is on a Dinan installed SC.

I found the vacuum hose to the blow-off value had broke. I attached the hose and my problems are gone. Car runs awesome now!

JOHN have you replaced the cats? I would definitely suggest throwing a fuel filter at is before a MAF at any price.

Side note: I just replaced a motor mount on my car yesterday, if yours is as bad as mine was you want to check to be sure the fan isnt hitting the upper radiator hose sometimes.

I have not replaced the cats yet. They do not rattle or sound like they are bad but im definately replacing them down the line. Im the 2nd owner, the 1st owner was an old lawyer that never took the car over 3000 rpm so they have not been abused (until me)

About the motor mounts. I had just replaced the tranny mounts with the UUC red race bushings and Im still getting a lot of shifter movement. Hell, sometimes i feel the tranny or something rubbing against the under side of the car. This is with the UUC bushings properly torqued and everything installed right. A bmw tech that now works at our honda carland looked at mine when i was doing my valve cover gaskets and plugs. He said they were totally fine but i disagree. Im getting the OEM tranny bushings and putting them in the car and see if that does anything different. I get a slight vibration with those damn race mounts when i asked for the street mounts.

So what is the story still no MAF? I am waiting to see what happens too. My car seems to do ok until 3000 RPM and then it seems like I hit a brick wall. One day I was going up a hill and was at 75mph and then tried to pass someone. I downshifted to 4th engine came up to about 3000 and I had it floored and the dumb thing actually started to slow down.....I didnt know what to think. I did replace one of my cats after it threw a code. No more code but also no change in accelaration. At about 1200.00 for one side I would say for 70 bucks try three of those dumb things. One thing I have noticed though is that when it hits that wall at 3000 rpm if I let off to about 1/4 throttle for 2-3 seconds and then get back on it it will run much better. Try that and let me know if yours does the same thing. I did try unplugging the MAF and I didnt notice any change at all, that is even with it unplugged, so I am still baffled. Now the reason it will run without the MAF is that the computer just goes into what GM calls "limp home mode." Just my 2 cents. If you could let me know about the backing off the throttle thing helping you.