Intermittent power loss and backfiring | FerrariChat

Intermittent power loss and backfiring

Discussion in '308/328' started by uberlink, Jun 11, 2013.

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  1. uberlink

    uberlink Formula Junior

    Apr 23, 2012
    777
    Twin Cities, MN
    Full Name:
    Mark Johnson
    #1 uberlink, Jun 11, 2013
    So I'm driving the 308 the other night. As I decelerate to a light, suddenly it feels like the engine is struggling to stay running -- RPMs drop then bounce back up a few times followed by a series of backfires. Just before this happened, I noticed a slight change in the exhaust note. The usual burble became somehow more 'boomy.' Hard to describe. Then it basically runs normally again for the rest of the drive. Next drive is fine.

    This morning, on my way to work, it does it all again. This time the RPM counter really pops up and down. When I disengage the clutch, the engine dies altogether. When I reengage the clutch and give it a little gas, it jumps back to life with a series of backfires and bouncing RPMs before it finally smooths out. I drive home, switch to my Audi, and head to work.

    What do you think might be up? I'm no mechanic, but I'm wondering if I'm having some kind of intermittent problem with the ignition. Other suggested diagnoses? Cures?
     
  2. stacy

    stacy Karting

    Nov 2, 2003
    104
    halifax
    #2 stacy, Jun 11, 2013
    Whenever this has happened to
    Me it has been a fouled spark plug or water around one of the plugs from washing the car or a problem with one of the spark plug extenders.

    Fouled plug less likely with injected car i would think
     
  3. vaccarella

    vaccarella Formula 3

    Apr 16, 2011
    2,291
    Full Name:
    Paul
    #3 vaccarella, Jun 11, 2013
    +1 on extenders. Pull the rear bank first and check the resistances. Very easy check to do.
     
  4. speedy

    speedy Formula Junior

    Oct 18, 2005
    625
    Plano, TX
    Full Name:
    James Gardner
    #4 speedy, Jun 11, 2013
    Agree with checking the extenders first.

    Have you had any issues with your battery holding charge after sitting for a period of time? (assuming you do not have it connected to a battery tender) If so, check your alternator. I found out the hard way that a failing alternator can produce similar symptoms to failed extenders.

    Good luck
     
  5. GrayTA

    GrayTA F1 World Champ
    Owner Rossa Subscribed

    Jun 25, 2006
    15,112
    Deep South
    Full Name:
    PDG
    #5 GrayTA, Jun 11, 2013
    Which car do you have?

    QV? i? or carbed?




    PDG
     
  6. ClydeM

    ClydeM F1 World Champ
    Owner Rossa Subscribed

    Nov 4, 2003
    10,588
    Wayne, NJ
    Full Name:
    Clyde E. McMurdy
    #6 ClydeM, Jun 11, 2013
    Sounds to me like a bank was dropping out.
    Did the SLOWDOWN lamps light?
    check the usual suspects: wires, cap (oil in it?) , rotor, coil, etc.
     
  7. alhbln

    alhbln Formula 3
    Consultant Owner

    Mar 4, 2008
    1,749
    Berlin, Germany
    Full Name:
    Adrian
    #7 alhbln, Jun 11, 2013
    Could be a ground issue of one of the MED801A Digiplex ignition units, a defective TDC or RPM sensor or a broken coil wiring or coil. The RPM counter wouldnt start to jump if there was a problem with the extenders as the RPM counter signal is generated by the Digiplex out of the TDC and RPM sensor signals.

    The backfiring as you describe it sounds more like an intermittent bank failure than a single cylinder failure which usually slows down the engine but does not necessarily end up in a series of backfires while driving. So this would also indicate a temporary failure of one of the Digiplex units.

    First thing to do would be to check and clean the Digiplex ground wiring/terminals, coil wiring/contacts, and inspect the king lead and distributor cap. If you can then borrow a known to be good MED801A and try it in place of your existing MED801A units (one after another) you should be able to easily find out if one of the MED801A Digiplex is broken.

    good luck,
    Adrian
     
  8. uberlink

    uberlink Formula Junior

    Apr 23, 2012
    777
    Twin Cities, MN
    Full Name:
    Mark Johnson
    #8 uberlink, Jun 11, 2013
    It's a 1980 gtsi. So 2v injected.
     
  9. jimpo1

    jimpo1 Two Time F1 World Champ
    Owner Silver Subscribed

    Jul 30, 2001
    24,532
    Dallas, TX
    Full Name:
    Jim E
    #9 jimpo1, Jun 11, 2013
    New spark plug wires fixed this on my 328.
     
  10. bentrm

    bentrm Formula Junior

    Sep 17, 2011
    596
    Pittsburgh, PA
    Full Name:
    Rob
    #10 bentrm, Jun 11, 2013
    My 83 QV did this when I first got it. It was a loose digiplex connector.
     
  11. Euro Quattro

    Euro Quattro Formula Junior

    Apr 20, 2005
    344
    Vancouver
    Full Name:
    Kent
    #11 Euro Quattro, Jun 11, 2013
    Check the fuel pump fuse, mine did the same thing & all it was is the fuse. I went to pull it out & it fell apart in my hand. Under one dollar fixed my issue on my 83 QV
     
  12. uberlink

    uberlink Formula Junior

    Apr 23, 2012
    777
    Twin Cities, MN
    Full Name:
    Mark Johnson
    #12 uberlink, Jul 3, 2013
    2NA sorted me out. He diagnosed it as deteriorated distributor rotors. He replaced those and also cleaned up contacts, checked wires, etc. She's back running strong again.

    While he was in there, he replaced the little thermal switch on the coolant expansion tank, and that seems to have improved the persistent high idle I used to have once the car warmed up. It's now idling warm around 1500 RPM, which is a lot more comfortable than the 2500 RPM it used to sit at.

    Thanks, 2NA!
     
  13. bentrm

    bentrm Formula Junior

    Sep 17, 2011
    596
    Pittsburgh, PA
    Full Name:
    Rob
    #13 bentrm, Jul 5, 2013
    Cool! Sweet relief.
     

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