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Discussion Starter #1
We have alittle trouble somtimes, well we allways uses to mutch fuel we think, we have a over all use of 5,9 km on 1 liter fuel, from freinds we know that the gennerel use should be arround 8 km on 1 liter fuel (normal use), maybe someone can coment on that ?

The second problem are that we feel it sometimes misses or hold back the power, from time to time it dos not have any power at all, when we reboot (restart) it is back to normal, and offen it just runs as it is soposet to.

we are driving with a modifyed rearsilensers and KN airfilters we have suspected the lambas but we have cheked them and no flars on them so i am very suspisios on the Air mass meters, dos anyone have a coment on this or have had the same problems ?

maybe a good place to by this meters if it is them.
 

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Does the exhaust sound very different (loud) when the power is down? If so, it is most likely the cam position sensor. Not expensive, I have replaced two so far.

Steve
 

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Hi,

Most likely the MAFs as you say. I had the same problems with my car, ordered new MAFs from California, and now it's a new car.

Rgds,
Kjell
 

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Does MAF affects the fuel consumtion as well? Because I'm having the same fuel problem... only getting around 350km per tank and the power sure doesn't feel like 400ps...
 

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If I understand correctly (DavidS would probably better explain), MAF's have a direct consequence on fuel consumption since the signal from them is used by the DME to directly control the amount of fuel injected into the cylinders. If the signal is off (incorrect), you can run rich (more fuel) or more lean (less fuel). Rich is better, lean is dangerous and in both cases, your consumption will change (more or, potentially, less).

Regards,

Gary.

Larry's M5 said:
Does MAF affects the fuel consumtion as well? Because I'm having the same fuel problem... only getting around 350km per tank and the power sure doesn't feel like 400ps...
 

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Discussion Starter #7
It looks like i need to install ned MAFs than - the other sensor that whare mensiont i have changed one two and for a very short wile i thourgh that the problem whare fixed - the power was back and the consomsion whare okay but onlu short. but my problem are not constantly - well the fuel use are but the lack of power is just some days, like it has its own life and have a bad day where it just dont feel like working.

I will change them and i can get back and tell if it worked.

Can you change them your self or do you need Mekanic skiles and computers to do that ?
 

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msport said:
It looks like i need to install ned MAFs than -
So you've tested the MAFs and they are bad?

What values did you get?
 

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Hello Msport!

You are in the city next to mine. If you have the time, let´s meet. I´ll bring a laptop with OBD software, and then with a bit of luck we will know exactly what is going on with the car. At least we can test the MAFs very accurately, even better than the fuel-flow test method.

Best Regs,

David
 

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I looked at Msport´s car. It seems the MAFs are fine. Got very high numbers on the fuel-flow test and when using the OBD-II scan-tool.

The car has the smoothest M5 gearbox I ever drove. It is simply perfect.

The engine feels very strong until it starts to hesitate. Hesitation is most evident at 5k RPM upwards. I suspect engine hesitation might be related to a coolant thermostat valve problem, which in turn increases coolant temperature and forces too much spark retard during WOT acceleration.

It could be a number of things:

A problem with the fuel tank breather valve. If that valve does not open correctly there will be a bit of vacuum in the fuel tank. This in turn will affect fuel pressure, and more so at higher RPMs.

Or it could be the fuel pressure regulator, or it´s vacuum hose connecting it to the intake.

David
 

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What a great board- and fantastic members. Kudos to DavidS.
 

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Larry's M5 said:
Does MAF affects the fuel consumtion as well? Because I'm having the same fuel problem... only getting around 350km per tank and the power sure doesn't feel like 400ps...
Larry,

Do you do a lot of city driving in slow traffic? If so, then 350 km/tank is normal.

David
 

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Discussion Starter #13
Acturly we do not drive alot of city traffic, normaly my wife has the beast, she have 5 km smalltown trafic and than 25 km freeway and the 2 km industry arier driving for work and very few stops.


But i was at Davids house the other day and we found out alot, the fuel comsomtion was alittle mystery and it was one of its better days it was running fantastic, well letter that eavening it began to lose power again - it hasnt done it since but it still uses a lot of fuel, David couldnt find any evedence to suspect the MAFs other than the KN air filters maybe can transfere alittle oil to the MAFs thay are very close to the filters - so i changed back to the old filters, just incase i have only once expiriensed lors of power, and is am again suspecting the MAFs for the fuel consumtion, so i will try o change them and keep you posted.

but right now it is running fantastic, we hit 280 km/H the other day and no problems about that:M5launch:
 

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Hi David,

Yeah, it's mostly if not all city driving over where I'm at. But still 350km/tank seems a little too much :p And I'm pretty much used to the power now and just not sure if it's performance is normal anymore LOL... Maybe I'll should clean the MAF for the heck of it, but the thing is I don't know what to use as cleaner since the recommended cleaner is not available over here :(
 

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Discussion Starter #15
Dear All


I have worked alot wit my wifes spoiled M5 now and changed the MAFs, well it sosnt seam to have effekt lorse somtimes like before and she drives 1,2 km longer pr. liter gas now so eaventhough it didnt give any showing on scans it might have ben semi or allmost gone. I can se now whare we have a more normal car it is very sensitive to city traffic so the 350 km tank sound right if you somtimes like to set some porsches or others streight along your way. But thanks specialy to DavidS for all his help.
 

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Msport,

This is extremely interesting, a car with good fuel-flow numbers still benefiting from new MAFs. The MAF sensitivity is evidently more complex than I have thought: I thought any car with good fuel-flow numbers had good MAFs.

Do you have any new fuel-flow numbers to compare with?

Cheers!

David
 

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Discussion Starter #17
Hi David


No i have not - i just changed them i didn´t have anything els to suspect, i am suprized to, i know a very expensive strategy but i wanted to rule that part out and the only way was to change them i had a freinds MAF in for a wile no change but we knew that thay whare most likly defect. But i worked and i have up to 8 km pr liter un long freeway runs and 7,3 in mixed driving so somting has change :thumbsup:
 

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Discussion Starter #19
Im not sure what you meen, but it endet with a change of the MAF and it got better economy, and was alot faster after. i had some problems about compleed loss of power at tree orcations but never after the change of the MAFs - i was very pleased about Davids help it was what help me suspect the MAFs after some reasearch - i havent got the tecnical story but went by intuision and it was a succes this time.
 
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