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348 stumbles at high rpm

Discussion in 'Technical Q&A' started by mr308gtb, Sep 13, 2010.

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  1. mr308gtb

    mr308gtb Formula Junior

    Sep 12, 2004
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    MeestahBig
    #1 mr308gtb, Sep 13, 2010
    I am moving this out of the 348 forum onto hear in hopes of getting a better answer. my 1994 348 hesitates and stumbles around 5800 rpm. no popping noise, just seems to go dead and then on, kind of bucks a little. A few times I kept my foot on the gas and it can sometimes power through it, but I didnt want to push it.

    the car run really really strong until this occurs and has no issues below 5500 rpm.

    I know there are mny issues/sensors that can cause a misfire, but given it only happens at hign rpm has to eliminate some of the possibilities?

    thanks, Marc
     
  2. Lawrence Coppari

    Lawrence Coppari Formula 3

    Apr 29, 2002
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    Lawrence A. Coppari
    #2 Lawrence Coppari, Sep 14, 2010
    Something simple: take a look at your spark plugs. I was at Road Atlanta last weekend. Friend had a supercharged BMW that was stumbling at high rpms. He removed the plugs to find one that had the insulator broken off on the center electrode inside the threaded section. He istalled new plugs and stumbling went away.
     
  3. FandLcars

    FandLcars F1 Rookie

    Aug 6, 2006
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    Rick Schumm
    #3 FandLcars, Sep 14, 2010
    I have a 348, but haven't read your thread over there, so not sure what's been suggested. However, can you tell if it's just 1 bank? If it is, perhaps it's something like an ignition/coil unit that's breaking down at higher loads/RPMs. If so, you could swap the units side to see and find out if the side changes. Also check all plug wires and other connections to make sure there is no slight ground that also gets bad at high RPM. Perhaps one of the generic electronic testers would allow you to drive the car and see if certain cylinders are affected. Just a couple thoughts. If you can't track it down, sometimes it is worthwhile to just take it to a dealer or independent knowledgeable with Fcars. Best of luck!
     
  4. Apples

    Apples Rookie

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    Terry Meeler
    #4 Apples, Sep 14, 2010
    check pick-up wire leads on crankshaft sensors, wire gets frayed and can break inside insulation on harness side.
     
  5. mr308gtb

    mr308gtb Formula Junior

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    MeestahBig
    #5 mr308gtb, Sep 15, 2010
    thanks... Im going to pull the ecu codes and thenprobably change out the crank sensors. someone else just commented on having the same exact issue and it was the crank sensors. odd to me that it affects on high rpm and not the start up and runningof the car in general. it may be b/c the sensor itself is not failing, its the connnection that is... and the connection comes loose at higher rpm.

    thx, Marc
     
  6. Emagdnim360

    Emagdnim360 Karting

    Jul 8, 2010
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    Banks
    #6 Emagdnim360, Sep 15, 2010
    Last edited: Sep 15, 2010
    I would remove your spark plugs and read them first; check your plug wires with a multi meter and then if all checks out I'd check for codes. If you have the codes handy post em up.
     
  7. Emagdnim360

    Emagdnim360 Karting

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    #7 Emagdnim360, Sep 16, 2010
    I sent you an email on what steps to do, if you have any questions pm me I'll be around.
     
  8. mr308gtb

    mr308gtb Formula Junior

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    #8 mr308gtb, Sep 17, 2010
    got it. thx for the reply. I am going to inspect the crankshaft sensors. I have new ones coming. I think this is most likely the issue. Marc
     

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