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Thread: Weak M50

  1. #1
    Join Date
    Dec 2006
    Location
    Long Island
    Posts
    319

    Default Weak M50

    '91 M50 5-speed ~200K miles

    Car operates great at 0-50% throttle.
    Step on the gas beyond that point, performance is the same.
    I cleaned the MAF and that helped some of the low speed sluggishness and made the engine more responsive.
    Idle is very smooth, revs up to redline with no issues but feels down on power with throttle openings greater than 50%
    Yesterday I reset the computer but it still performs the same, flat.
    There are no warning lamps illuminated on the dash.

    Does anybody have any suggestions on where I should start diagnosing the problem? I was thinking to test the resistance of the TPS potentiometer to make sure it is working properly but other than that I'm not so sure what could be causing the issue.

    Has this situation happened to you?

  2. #2
    Join Date
    Mar 2006
    Location
    Derbyshire, UK
    Posts
    872

    Default

    Check the fuel pressure.

    1997 535i V8
    5spd, OBC, A/C, cruise, BMW phone, factory M-Tech wheel & suspension, 18" Alpinas

  3. #3
    Join Date
    Apr 2006
    Location
    Chicago, Il. U.S.A.
    Posts
    4,243

    Default

    x2 also check for restricted exhaust.
    "The gas pedal wouldn't go to the floor if it weren't meant to be there"

  4. #4
    Join Date
    Nov 2006
    Location
    Germany
    Posts
    475

    Default

    Quote Originally Posted by Ross
    x2 also check for restricted exhaust.
    Seen an Audi Quattro that the owner brought it in cause it started running like a dog. Had no legs on the the top end and sounded kind of quietly funny.

    The muffler was full of dry dog food! We had to get a new muffler for the poor guy because all of the moisture in the exhaust had caused the food to swell and stick in place so no shaking the food out. That was the heaviest muffler I've every felt...

    Brian

    P.S. I've seen a Saab with the same symptoms from a crimped exhaust (half way shut) due to backing into a curb and bending the pipe under the back seat. You really couldn't tell anything was wrong without lifting the car.

  5. #5
    Join Date
    Jan 2004
    Location
    Thunder Bay, Ontario
    Posts
    2,538

    Default

    Quote Originally Posted by bsell
    The muffler was full of dry dog food! We had to get a new muffler for the poor guy because all of the moisture in the exhaust had caused the food to swell and stick in place so no shaking the food out. That was the heaviest muffler I've every felt...
    OK, I'll 'bite'. How do pack enough kibble in an exhaust to block it?

    One determined and creative pranskster?

    Mufflers shipped on greyhound

    Dave

    10/90 Build 525im, 630,000+km, Eibach/Sachs, Engine Rebuild
    *RIP Oskar the DOG *

  6. #6
    Join Date
    Jul 2006
    Location
    El Paso TX
    Posts
    1,534

    Default

    MIce/ rats

  7. #7
    Join Date
    Mar 2006
    Location
    Ann Arbor Michigan
    Posts
    218

    Default

    I agree with Dave on this. Sounds like low fuel pressure.
    SOLD!

  8. #8
    Join Date
    Nov 2006
    Location
    Germany
    Posts
    475

    Default

    Quote Originally Posted by Dave M
    OK, I'll 'bite'. How do pack enough kibble in an exhaust to block it?

    One determined and creative pranskster?

    Mufflers shipped on greyhound

    Dave
    The owner found evidence of mice living in his garage. I can't imagine how they carried the food into a muffler opening about one foot off the ground...

    Brian

  9. #9
    Join Date
    Dec 2006
    Location
    Long Island
    Posts
    319

    Default

    Quote Originally Posted by DaveVoorhis
    Check the fuel pressure.
    will do. we just got dumped with some ice here on Long Island so hopefully I can get to it tomorrow.

    I'm hoping it is simply a clogged filter. Here's some observations which point to fuel supply.
    Driving on highway, 2500rpm, 4th. Punch throttle, mediocre acceleration.
    same situation, let off for 2 seconds, punch throttle, better acceleration but fizzles out.
    Being as the car was a neglected orphan that I adopted, i'm sure that filter replacement will yield better performance and economy.

    i'm also going to get a gauge with a longer hose so i can tape it to the cowl and observe pressures while driving.

    thanks to all who replied, i'll let you know how it goes

  10. #10
    Join Date
    Feb 2004
    Location
    Wichita KS
    Posts
    180

    Default

    Oh yeah, crudded up plugged filter is a possibility. I can't imagine the original going 200K, but car could be neglected to that extent.

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