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Thread: 91 M5 problem during full acceleration, help appreciated

  1. #1

    Default 91 M5 problem during full acceleration, help appreciated

    Well this year I finally decided to enjoy my 91 M5 with 52k miles. For the past 3 years of ownership, it has been a garage queen, pampered. Lately, I have been driving it often, putting anywhere from 100-150 miles each time I take it to work. It has been running flawlessly, as would be expected from a car with only 52k miles and extremely clean.

    Today however, I noticed that under full throttle, in third gear, at around 5500rpm it lost power, like when you drive a car that is very low on gas and it is ready to quit. At first I thought it may be wheel slip due to uneven pavement under hard acceleration.

    Over the next 10 miles or so, I tried a few more times to duplicate the problem and sure enough, only under full throttle, accelerator fully depressed, at 5500rpm it would loose power, in second, third or fourth gear, it seemed to be getting more pronounced. Other than at 5500 rpm though, the car pulls strong like usual, throughout the rest of the rev range.

    Three hours later on my way home, I tested it again and only under full throttle, it lost power but it seemed even more pronounced. Over the next twenty miles or so I tried gradual acceleration and the car runs fine, from stand-still to 6500.

    So my problem appears to occur only under full throttle at 5500rpm, other than that, the car runs strong and seems fine.

    What could be the problem?? The car needs nothing, all maintenance is current, fuel tank is full, gas is 93 octane.

    Thanks in advance.
    Last edited by icm5er; 02-04-2007 at 11:31 PM.

  2. #2
    Join Date
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    Fuel filters clogged or a weak pump.

    injectors dirty? think it would be more like every test though.
    95 E34 530I V2.31
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  3. #3
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    ditto

    Quote Originally Posted by 632 Regal
    Fuel filters clogged or a weak pump.

    injectors dirty? think it would be more like every test though.
    all america wants is cold beer warm cat and a place to take a poop with a door on it

  4. #4
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    With the hood open where you can see the actuator for the resonance flap. It's on the side of the plenum. Turn the key to "run" position and see if it cycles twice. If it cycles, it's ok...then the next thing to check is your rotor cap and plugs. It sounds like it's flooding instead of a no gas situation, since a gradual application of pedal to WOT doesn't duplicate the problem.

    I'm sure it's something simple Ivan, good luck with her!

    Jr
    '91 ///M5

  5. #5
    Join Date
    Dec 2003
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    Chicago
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    You might also want to check the coil. It sits above the exhaust header so it can get hot and add to that the high rpms of the car, it can fail prematurely compared to the M30s. With Jr's explaination of a flood situation, this would support the notion as there wouldn't be enough spark to burn the gas. It can be difficult to check as coils can sometimes only show that it is bad under increased load and/or high rpms. You can do a visual inspection and see for a cracked or melted casing. Otherwise, changing one for a healthy one is the only other way to determine. I have seen this situation on the S38 and the M30.
    Brandon J

  6. #6
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    Coil caused this on my 535. Ran fine up to certain RPM then lost power...

  7. #7

    Default Problem with power "gap" gets worse...

    Quote Originally Posted by icm5er
    Well this year I finally decided to enjoy my 91 M5 with 52k miles. For the past 3 years of ownership, it has been a garage queen, pampered. Lately, I have been driving it often, putting anywhere from 100-150 miles each time I take it to work. It has been running flawlessly, as would be expected from a car with only 52k miles and extremely clean.

    Today however, I noticed that under full throttle, in third gear, at around 5500rpm it lost power, like when you drive a car that is very low on gas and it is ready to quit. At first I thought it may be wheel slip due to uneven pavement under hard acceleration.

    Over the next 10 miles or so, I tried a few more times to duplicate the problem and sure enough, only under full throttle, accelerator fully depressed, at 5500rpm it would loose power, in second, third or fourth gear, it seemed to be getting more pronounced. Other than at 5500 rpm though, the car pulls strong like usual, throughout the rest of the rev range.

    Three hours later on my way home, I tested it again and only under full throttle, it lost power but it seemed even more pronounced. Over the next twenty miles or so I tried gradual acceleration and the car runs fine, from stand-still to 6500.

    So my problem appears to occur only under full throttle at 5500rpm, other than that, the car runs strong and seems fine.

    What could be the problem?? The car needs nothing, all maintenance is current, fuel tank is full, gas is 93 octane.

    Thanks in advance.
    Today car ran fine, first time driven since last post, I did not push it to WOT, I have not had time to do anything with the car. I drove it about 60 miles, no problem, then about 8 miles from home, it ran very rough at a stop light. I had to keep it around 2000rpm to keep from stalling. A few times it almost stalled, I had to play with the throttle to keep it running, it is stumbling bad.

    I kept my fingers crossed, replaced the fuel filter, to no avail, still running very bad.

    I guess I will not make it to the NYBMWCCA meet tomorrow at the vinyard.
    This sucks.

  8. #8
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    Have you done the stomp test to check for any codes? The problem occurred once the car warmed up?...Hmmm I would check the codes. It could be a sensor such as the coolant temp sensor, or the MAF or even bad gas-like getting sut from the bottom of a gas station tank. Again, it could have been the coil still and was affected once it got hot over the exahust manifold. Check the codes.
    Brandon J

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