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Testarossa Power Loss

Discussion in 'Technical Q&A' started by UIUC, Jul 6, 2007.

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  1. UIUC

    UIUC Karting

    Jun 12, 2006
    50
    Roswell, Ga
    Full Name:
    Wyatt P Schupbach
    #1 UIUC, Jul 6, 2007
    About a week ago I had my 86 Testarossa out for a drive. Everything seemed fine until I got on the gas and hit 4700 RPM. At that RPM the power just dropped off like someone hit the choke switch. I took the car up and down the power band a few times each time I lost power at around 4500-5000 RPM. Any ideas on what can cause this? Anyone had a similar issue?

    I believe both cylinder banks are firing as each and every inlet manifold heats up evenly as I start the car. (may not be 100% foolproof) I've checked for loose wires in the engine bay, the boot, and under the passenger footrest + no blown fuses. I did notice one spark plug wire loose but have verified that that cylinder is hitting (like the other 11).

    I did recieve a nasty shock from my coil when I grabbed the distributor supply wire. Possibly there is a short in the coil, but why would it only affect the car at high RPM? I could still have a plug fouled - so I could pull individual plug wires and see if the engine tone changes but the car winds up well until 4500. The car ran great a week before this and the engine-out service was less than a year ago, so all the filters are "new".
    Could this be the coil? The fuel filter or pump? Vacuum leak? I hate to start pulling parts off and swapping them or testing fuel pressures etc without getting some direction. Thanks-
     
  2. Jeff Pintler

    Jeff Pintler Formula Junior

    Jul 20, 2005
    537
    Richland
    Full Name:
    Jeff Pintler
    #2 Jeff Pintler, Jul 7, 2007
    Sounds like you know the things to check. You just have to start working through the list. When I tore my ignition system apart, I found the spring backing the carbon electrode broken in the cap, both carbon electrodes very short (worn out) and even the wire from the coil to the cap had burned away in the center. Check the condition of the rotors and dirty electrodes in the cap. The fact that acceleration is good up to a certain rpm might imply the fuel pumps are ok. There is a vacuum line from driver's plenium to the ignition ecu (driver side) that might affect advance. Maybe one bank is cutting out at a certain rpm, either ignition or Jetronix (fuel ecu on pass side). It's probably is something simple. Good luck!

    Jeff Pintler
    89 348tb, 86tr
     
  3. testarob

    testarob F1 Rookie

    May 13, 2006
    2,504
    Debary, Florida
    Full Name:
    Rob
    #3 testarob, Jul 7, 2007
    Double check the fuel filter as this happened right after getting gas. I had a bad batch of gas once that put trash in the fuel line.
     
  4. UIUC

    UIUC Karting

    Jun 12, 2006
    50
    Roswell, Ga
    Full Name:
    Wyatt P Schupbach
    #4 UIUC, Jul 14, 2007
    Thanks for the insights. I decided it was best to go ahead and call a mechanic lest I make matters worse. After looking the car over he found that the temp sensor had went bad and was telling the ECU that the car was at 40F instead of operating temp. As a result, the ECU was feeding too much gas to the cylinders and fouling them out.

    I'm told that the fouled plugs may have eroded the distributor buttons as those are paper thin now as well. So it's a temp sensor, new distributor components, and possibly a bad oxygen sensor too. I guess it's unlikely I would have found the problem as it wasn't going to be among the items I was to check. Parts arrive next week. Hopefully all is well by Wednsday. Thanks again.
     
  5. rosso tweeks

    rosso tweeks Rookie

    Aug 24, 2006
    25
    SFV/CALIF
    Full Name:
    JOHN
    #5 rosso tweeks, Jul 15, 2007
    All sounds like a very good diagosis, but would also recommend checking the "cats" due to extra rich mixture in exhaust system. If your plugs were fouled, chances are pretty high your catylitic converters are contaminated.
    Hope cats are OK, good luck.
     
  6. UIUC

    UIUC Karting

    Jun 12, 2006
    50
    Roswell, Ga
    Full Name:
    Wyatt P Schupbach
    #6 UIUC, Jul 17, 2007
    The catalytics are in a box in my attic so that's at least (1) bullet I dodged......Hopefully, I never have to certify my emissions.

    The car also needs a coil. The left bank is pretty light on voltage as the test ligh was barely lit on that side. Once that arrives I should be good until the next expenditure. You have to love Italian parts pricing. Thanks for the help on this one.
     

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