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1994 348 spyder misfire or backfire at 5000 RPM

Discussion in 'Technical Q&A' started by Bill Gelinas, Jul 15, 2020.

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  1. Bill Gelinas

    Bill Gelinas Rookie

    Aug 2, 2006
    6
    Ontario Canada
    Full Name:
    Bill Gelinas
    I have come for advice on this one as i hope someone has seen this before, my car just had a major service 300 miles ago, has been driven a dozen times runs really well, last outing when car hit 5000 rpm it missed or backfired and the 1-4 slow CEL blinked on and off with the frequency of the miss or popping. So i assume i am getting some raw fuel into the cat and the temps rose as it missed. I am aware of the many items it can or could be, I checked codes first only had codes for cat temps, Light did not ever stay on just blinks if it misses and if i drop back under 5000 all seems well no light. car has 23k on it. If anyone has seen this symptom whats your opinion on what is most likely culprit. Coils, wires, 02 sensors, and coil modules, crank sensor, cam phaser are all original, I suspect its a electrical missfire malfunction but could be fuel starvation? or CAM jumped (god i hope not) broken valve spring- just as bad.....any help would be greatly appreciated. I have read most info i can find on this and see not reports of missing over 5000 rpm specific. Car idles and sounds completly normal up to 5k. Thanks all
     
  2. Qavion

    Qavion F1 Rookie

    Feb 20, 2015
    3,653
    Sydney
    Full Name:
    Ian Riddell
    Bill, are you sure it's not the other way around.... cat temperature causing momentary bank shutdown?

    I don't know how the ECU responds to momentary temperature spikes, but one of the most common problems on these cars are faulty thermocouple ECUs. Try interchanging these to see if the problem swaps banks.

    If you think it's an ignition problem, swap the coilpacks or ignition modules. The duplication of components on these cars makes faultfinding a little easier.

    Try posting your question on the 348/355 forum. You may get more responses.
     
  3. brian.s

    brian.s F1 Rookie
    Professional Ferrari Technician

    Nov 3, 2003
    3,751
    Midwest
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    Brian
    Crank sensor probably
     
  4. Bill Gelinas

    Bill Gelinas Rookie

    Aug 2, 2006
    6
    Ontario Canada
    Full Name:
    Bill Gelinas
    Yes, both good places to start, i got a pair of the kia sensors, and will try them, also will the car run with the 02 sensor computers disconnected to test the theory of the ECU causing the miss....... or the miss causing the ECU to turn on light. ?
     
  5. Bill Gelinas

    Bill Gelinas Rookie

    Aug 2, 2006
    6
    Ontario Canada
    Full Name:
    Bill Gelinas
  6. Bill Gelinas

    Bill Gelinas Rookie

    Aug 2, 2006
    6
    Ontario Canada
    Full Name:
    Bill Gelinas
    Problem solved, so the issue was the Bank 1-4 crank sensor had a broken wire inside the rubber boot of the wiring harness leading up to the crank sensor, surprised it even ran on that bank, looks like possibly it had a partial ground signal with the body of the metal sensor. Easy fix but no reason for the wire to be broken its fully supported covered and insulated, just pure vibration over time snapped it at the crimp point. It was very hard to get the pin out of the plug. However once out I realized the pins are the same as my spare parts bin of stuff I have for my Saab 9-5 seat heater switch so robbed one from there to mend the harness. Runs perfect again. Thanks for the input. Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
     
    Qavion and Wade like this.
  7. Wade

    Wade Three Time F1 World Champ
    Rossa Subscribed Owner

    Mar 31, 2006
    31,355
    East Central, FL
    Full Name:
    Wade O.
    That's awesome to hear.


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