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Discussion Starter #1
I'm the original owner of an early 2001 model M5 that will be 5 years old in September, and obviously out of warranty. It just turned 30K miles, and has only ever had the oil changed and new tires added.

The problem is that the engine now runs roughly when accelerating at less than 2000 RPM -- for example, when trying to accelerate between 1500 and 2000 RPM the car feels like it's bucking and shaking.

Above 2000 RPM during acceleration everything smooths out. It still seems to have respectable higher-RPM power, and still idles smoothly. No "check engine" light (I had VANOS replaced twice under warranty early on.) or other signs of problems.

Any ideas? Could it be dirty MAFs?

Thanks,
- Dave
 

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FlyM5 said:
Any ideas? Could it be dirty MAFs?

Thanks,
- Dave
Yes it could!
If you're out of warranty and plan on doing any work yourself on the car, you need a code reader. Peak makes a nice one. You can have fault codes without an SES light, and they would certainly point you in the right direction.

There does seem to be a way to read fault codes thru the obc (search for "unlocking the obc") but i have yet to find a site that lists the fault codes that come up in the diagnostic test.
Mike
 

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Sounds like it is time to clean your MAF sensors. Won't cost you anything and it is more than likely the problem anyway. As for the code reader I second the Peake tool, wonderful functionality and company to deal with...
 

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I agree about getting a code-reader. Get one that can display and log real-time engine data too, not just the fault-codes.

(see for example
www.obd-2.com
I use their "Model ISO", which runs on a laptop and costs about $100)

The problem on your car could actually be a combination on low fuel pressure and contaminated MAFs. Try cleaning the MAFs first.

It should be fairly cheap to test the fuel pressure. Have it done with and without the vacuum hose coonected to the fuel pressure regulator.

Pressure should be 5.0 bar with the vacuum hose connected and 5.5 bar without it. If the measurements are off, get a new fuel pressure regulator. (Costs about UD$ 60, I think, plus a little labor. While you are at it you might just as well replace the fuel filter.)

If the measurements are very much off, it could be the fuel pump too.

David
 

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Discussion Starter #5
Thanks for all the great advice, but I'm afraid things are now more serious than originally thought.

I learned how to use the instrument cluster in the car as a way to test the MAFs, by viewing the fuel consumption per hour and driving wide open throttle to the readline.

In 2nd gear with the digits changing wildly I saw either 134 or 136 liters/hour before hitting the rev limiter, which is close enough to the desired 140 liters/hour. That would seem to rule out bad MAFs, especially as I only have 30K miles on the car. The car appeared to have plenty of power at higher RPMs.

I then replaced the air filters, just to make sure dirty filters weren't somehow causing the bucking/roughness in acceleration below 2000 RPM. They didn't make any difference.

So on the way home this afternoon, I gave it one more run to the redline in 2nd gear while viewing the fuel consumption in liters/hour. Just as I got to about 5000 RPM and about 80 l/hr., the car suddenly lost power and the SES light came on!

I was barely able to drive it home -- rough idle, very little power -- I had to keep the revs above 3000 just to get up a steep hill. It sounds horrible while idling.

Looks like it's going to the dealer on Monday (tomorrow). My guess is it's the VANOS, which promises to be a very expensive repair. As I mentioned earlier, I've already had the VANOS replaced twice a few years ago when the car was under warranty, but the engine never ran this poorly. I sure hope it's nothing more serious.

(And it's my birthday -- what a "nice present" to have the car do this today).

- Dave
 

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It doesn´t have to be really bad. Try to enjoy your birthday anyway!

It could very well be the camshaft sensors (not very expensive), or the fuel pressure regulator ($60).

Don´t let them touch the Vanos units until they are positive the camshaft and crankshaft sensors are working properly.

It could also be a low fuel pressure problem. It is easy to check the fuel pressure.

It is actually good for you that you got a SES light. There will be a fault-code stored that might give a clue to what is going on.

David
 

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At 30k you should probably perform the Service II. Plugs, belts, hoses, all fluids etc., etc. - Good luck I hope you find the reason your car is running rough. Keep us posted!
 

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Dave,

Belated happy birthday to you. What you described: car loosing power at 5k RPM, SES lights on are the exact symptoms when my MAFs failed.

I was doing brake pad bedding and rotor cleaning runs when that happens. Needless to say, I had lousy brake squeals, rotor shimmies, and a limp engine all at once. What one can definitely call a bad-car day. :mad: :mad: :crying: :crying:

Hope you solve your issues soon. MAFs are the bane of the E39 M5s.

CP
 

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chunpng said:
Dave,

Belated happy birthday to you. What you described: car loosing power at 5k RPM, SES lights on are the exact symptoms when my MAFs failed.

I was doing brake pad bedding and rotor cleaning runs when that happens. Needless to say, I had lousy brake squeals, rotor shimmies, and a limp engine all at once. What one can definitely call a bad-car day. :mad: :mad: :crying: :crying:
CP
This is really interesting to me, as i have had several issues crop up while bedding in brake pads. First time, with the new bbk, hard stop from 80-10, start to accelerate and i have a mis, rough idle, ses light. Shut off and restart and all is fine. I had just gotten the car back from the dealer, literally, earlier that day with new mafs. I headed straight back, got a call the next am saying i needed a vanos.

Next issue, on the track, sears point, just after turn 7, hard braking hairpin, go back to accelerate, car misses, ses, pull into pits, shut off and restart. All was fine, a couple of sessions later, same thing. Miss after hard braking...

Foward to last night, new pads and rotors, went out to bed them in. After my third stop, accelerating, moderately, about 4k rpm, miss, ses etc. Shut off and restart all is fine. Drive the heck out of the car for another 15minutes, no issues.

Pong, your mention of bedding in brakes has me thinking, i wonder how hard decelleration could be linked with a miss.
On all of my occasions, my peak tool told me cyl 1 misfire, nothing more. I went to the dealer after my track miss, the gt1 told them "cyl 8 misfire with cyl shutdown" and also cyl 4 misfire with cylinder shutdown...
This is interesting.
mike
 

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kees said:
Misses after braking sound more like bad fuel stirred up in the tank.
On a vintage car possibly, but most unlikely on a modern BMW. The fuel-pump continously sucks petrol from the bottom of the tank, and pushes the fuel into the fuel line at a flow-rate that is more than the WOT fuel consumption. Then the fuel-pressure-regualtor lets the excess fuel (the fuel not entering the engine through the injectors) recirculate back to the fuel tank through the fuel return line.

This means fuel is continously moved from the bottom of the tank through the pump and fuel filter and back to the top of the fuel-tank. Any solid contaminants will get caught in the fuel filter, and any liquid contaminants will be mixed with all the fuel and burnt in the engine.

As the cause of the problem, my bet would be on a bad crankshaft sensor, or a bad fuel-pressure regulator, once the MAFs are ruled out.

David
 

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Discussion Starter #12
Further info on the engine problem from the dealer:

The car had gone into limp mode after a misfire on cylinder #6 during my wide-open throttle run to the redline. Upon restart it's no longer in limp mode.

The dealer replaced both MAFs (before asking me) and claims that the car now runs fine (I can't verify this yet, as I'm out of town until Thursday and can't drive it yet.). But since I had previously seen fuel flow of 136 liters/hour during a WOT run to the readline on Sunday, does this make sense?

The dealer's willing to put my old MAFs back in and not charge me $500 apiece if I want to try cleaning them.

Your thoughts? Is MAF cleaning effective, or am I better off having them replaced for $1000. The dealer's mechanic claims that cleaning doesn't really work.

- Dave
 

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The dealer's willing to put my old MAFs back in and not charge me $500 apiece if I want to try cleaning them.

Your thoughts? Is MAF cleaning effective, or am I better off having them replaced for $1000. The dealer's mechanic claims that cleaning doesn't really work.

- Dave[/QUOTE]
I got both MAFS for $616 at the dealer - I'd raise hell if they charged that much.
 

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FlyM5 said:
But since I had previously seen fuel flow of 136 liters/hour during a WOT run to the readline on Sunday, does this make sense?
If this is the case, then the arguement isn't 'new MAFs' versus 'cleaning MAFS'... 'it's MAFs are fine, what is the real problem'.

As I read the maf cleaning post, the fuel consumption is related to MAF function, and it seems your fuel consumption is OK. Did the dealer indicate what hard data told him your MAFs were bad (other than the fact that you are a cash customer and BMW isn't going to demand the dealership provide evidence of tru failure...)

My 2 cents
 

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I think Kees and Ard are right, why pay $1k for a $350 & 20 min DIY job?

With such a good fuel-flow figure, I rather doubt the MAFs are to blame in this case.

David
 

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DavidS said:
I think Kees and Ard are right, why pay $1k for a $350 & 20 min DIY job?

With such a good fuel-flow figure, I rather doubt the MAFs are to blame in this case.

David
I agree also, unlikely MAFs, but if so, $350 is the right amount of money, if they do it, add 1 hour labor, or say $500 installed, not $1000.
Regards,
Jerry
 

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or have them put the old MAFs back in (yeah, he is positive you will not call his bluff) and then one of us can call their parts counter and inquire "Do you have any lightly used MAFs for sale?"

:)

Adam
 

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are there any fault codes present? What is the dealer going on, other than the history? If there is no fault code, and you have original mafs, they could be intermittently giving an issue. It's not uncommon to have mafs probs without codes. If there is a code, i'd like to know what it is!
Mike
 

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gsfent said:
I agree also, unlikely MAFs, but if so, $350 is the right amount of money, if they do it, add 1 hour labor, or say $500 installed, not $1000.
Regards,
Jerry
There is an important difference: $1k gets 2 MAF sensors including MAF housings (which you don´t need to replace). $350 gets you just the two MAF sensors.

I think there is a BMW service bullitin forbidding the disassembly of the MAF housings alleging difficulty to align the sensor afterwards, (which is absolute total nonsense) so I would not be surprised if the dealer service will refuse to do anything except replacing the MAFs including the housings.

To replace the MAF sensors while keeping the housings is an extremely simple procedure. It is far easier than an oil change. It is about as time consuming as filling up fuel and washer fluid.

1. Buy the 5-lobe + 6-lobe MAF bit kit ($13 something) from

Part MN565600 - MAF Bit Kit (found a bit down on this page)
http://shop.metalnerd.com/index.cgi?code=3&cat=5

www.metalnerd.com

2. Buy MAF inserts from Continental Imports. ($350 for two).

3. Open bonnet. (hood) Pull connectors from the old MAFs. You need to press on a tab to make the connector release. Use fingers, not tools.

4. Unscrew the four screws holding the MAF sensors in place. For this you will need to use either the 5-lobe or 6-lobe bits plus a standard bit screwdriver.

5. Pull the old MAFs out from the housings. Just a straight smooth pull. Use fingers, not tools.

6. Put the new MAF inserts in. Those only fit the screw-holes in one direction.

7. Put the screws back. Torque gently.

8. Put the connectors back. Make certain you hear a distinct click.

9. Drive the car at speed for 20 minutes. During this time the DME (ECU) will learn the new MAFs.

10. Enjoy the new horse power.

It would really bug me if you have to overpay $5-600 for this...
If you do this yourself, and the work (excluding the drive, which you would have to do yourelf anyway) takes even 30 minutes, you would still net $1200 per h. Tax-free. That is a pretty cool pay...

David
 
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