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Tach Operating Eratically...Then Car Backfires

Discussion in '308/328' started by Owens84QV, May 27, 2007.

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  1. Owens84QV

    Owens84QV F1 Rookie

    Oct 2, 2001
    4,486
    Somewhere in NC
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    Greg
    #26 Owens84QV, Jul 1, 2007
    Nick...what's one of these systems cost?

    The next time my Marelli system flakes, I may just take the plunge and do it. Are the instructions pretty clear for a decent shade-tree mechanic to follow?
     
  2. Owens84QV

    Owens84QV F1 Rookie

    Oct 2, 2001
    4,486
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    Greg
    #27 Owens84QV, Jul 20, 2007
    Well, at first I thought it was solved...until I drove over some rough road and the problem came back. Then it hit me...everytime this problem has happened, it was when I ran over a rough patch of road or rumble strips. It must be a loose connection someplace.

    Fast-forward 1 week....

    SOLVED!!...the main problem I believe was loose battery cables. Last weekend, just for the heck of it, I inspected the battery cables and noticed that they were really loose, and, judging by the clamps, they weren't getting any tighter.

    I also read a separate thread on F-chat where someone was investigating the use of copper shims around the battery posts to improve thier connection.

    I then Googled "battery post shims" and was able to find them at the local Autozone. With the battery post shims installed and all of the connections clean and snug, she's been on two test drives over some pretty bumpy roads and all is well. Yehhhh!
     
  3. Birdman

    Birdman F1 Veteran

    Jun 20, 2003
    6,689
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    THE Birdman
    #28 Birdman, Jul 21, 2007
    Wow, weird!

    I would have bet money it was something between a crank sensor/ECU because the erratic tach is a dead giveaway. So the voltage was dropping and freakin' out the ECUs. Makes sense, but a tricky thing to find...at teh wrong end of the car!!

    Good job troubleshooting.

    Birdman
     
  4. Owens84QV

    Owens84QV F1 Rookie

    Oct 2, 2001
    4,486
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    Greg
    #29 Owens84QV, Jul 23, 2007
    The sad part of the story is that several weeks back, I thought of looking at the battery but thought...nahhh, it can't be the battery. Dummy me...
     
  5. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Three Time F1 World Champ
    Owner Rossa Subscribed

    May 4, 2001
    36,253
    Birmingham, AL
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    Tommy
    #30 Dr Tommy Cosgrove, Jul 24, 2007
    Sorry for the delay - mine was a bad flywheel sensor. The one at the 11:00 position. I replaced it and installed the two new coils just because I had them. Now it runs fine, it just won't idle worth a crap. I think it is just WAY too rich but I don't have any idea why that problem has all of a sudden presented itself. I am getting a black soot on the back of the car and my eyes burn from the exhaust like it has a test pipe again (it doesn't, I have a hyperflow).

    This now presents me with a different problem - setting the CO correctly. With the test pipe I could simply use my muffler as the opening I needed to snake the sniffer into but I can't now. Years ago I had the little exhaust pipes on the front bank rust thru so I had them removed and the holes welded up. Where do I get an exhaust sample now for the whole engine?

    (and no I don't want to set my CO "by ear" either. How do you "hear" a 2% change vs a 5% change?)
     
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