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My Testarossa engine cuts at 3800 rpm

Discussion in 'Boxers/TR/M' started by Dadster, Jun 29, 2020.

  1. Dadster

    Dadster Rookie

    Sep 16, 2017
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    S Evans
    Hi all,

    I have a 1990 testarossa and I am currently waiting for a mechanic friend of mine to look at it. I thought it might be good to consult the experts on this board before he does. Any thoughts or advice is appreciated.

    The car drives perfectly below 3800 rpm. Car has 22000 miles. It is in very good condition. All the cats are hollowed out. There are no warning lights on the dash. It has new fuel pumps, distributor, fuse box and other ignition related components.

    When you drive in any gear or under any load the engine will cut out when it reaches 3800 rpm...its like a rev limiter of sorts. If you rev the engine when in neutral then the engine also cuts out at 3800 rpm...the revs rise through it but then fall back down and the engine fires up again and it oscillates smoothly between 3500 or so to 4500 or so.

    The 3800 rpm is a rough estimate,,,it might be 3850 or 3900 but it is just below 4000.

    Maybe a wire is broken or a connection lose to the control units.? Is there a cold start limit that is not turning off.?

    Any thoughts appreciated,
     
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  3. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
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    not that I know

    can not imagine this.
    if it is handling like a rpm limiter as you write then I think you may first check the 2 sensors at the flywheel. I not think the problem are the ignition wires. may be the fuel pumps get stopped because of wrong infos?
    check if it is a fuel or an igniton problem. take a stroboscope light, connect to one cylinder and let the engine run, accelerate and when the engine then stalls have a look if the strobelight still is flashing.
     
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  4. Veedub00

    Veedub00 F1 Rookie
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    I'd make sure those 2 electrical connections underneath the coolant reservoir are clean too. Those signals go through them.
     
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  5. Ianjoub

    Ianjoub Formula Junior

    Dec 22, 2019
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    Homosassa, FL USA
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    Ian Joubert
    I think he means a timing light on a plug wire. You can also get a set of noid lights to see if injectors are getting signal.
     
  6. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    No electrical signal used by CIS injectors, but agree that the logical first diagnostic step would be to just confirm/deny spark on both banks when the problem occurs.
     
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  8. vincenzo

    vincenzo F1 Rookie

    Nov 2, 2003
    2,964
    Upon hearing this:
    “All the cats are hollowed out.”

    It reminds of the first ‘major’ that I paid an independent professional to do. He claimed the precat was damaged and he hollowed it out as a ‘repair’.

    Later, FoS said that the car would not meet emissions standards on a gas analyzer. They diagnosed it as bad cam timing. They were correct. The bad timing had put excess fuel through the cat and burned ‘em up.

    Several sequential things I would check to address your issues:
    1) Check connector under your expansion tank to ensure it is clean and tight.
    2) Check plug wires for continuity and resistance. Check inside your distributor caps for any carbon tracking or dirt/oil as well as the center button.
    If that fails to fix it....
    3) Get a gas analysis to ensure everything is right. This is only suggested because of your hollowed out cats.
     
  9. Ianjoub

    Ianjoub Formula Junior

    Dec 22, 2019
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    Homosassa, FL USA
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    Just read up on these, learn something new every day!

    https://en.wikipedia.org/wiki/Jetronic

    "Fuel is pumped from the tank to a large control valve called a fuel distributor, which divides the single fuel supply line from the tank into smaller lines, one for each injector. The fuel distributor is mounted atop a control vane through which all intake air must pass, and the system works by varying fuel volume supplied to the injectors based on the angle of a moving vane in the air flow meter, which in turn is determined by the volume of air passing the vane, and by the control pressure. The control pressure is regulated with a mechanical device called the control pressure regulator (CPR) or the warm-up regulator (WUR). Depending on the model, the CPR may be used to compensate for altitude, full load, and/or a cold engine. The injectors are simple spring-loaded check valves with nozzles; once fuel system pressure becomes high enough to overcome the counterspring, the injectors begin spraying."
     
  10. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
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    romano schwabel
    when you test then disconnect the O2 sensors
     
  11. Dadster

    Dadster Rookie

    Sep 16, 2017
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    S Evans
    Update...

    Timing checked - all good.

    Found fuel just turns off at 3800 due to tachometric relays switching off. when these relays are bridged the engine runs perfectly...
    so something is causing these to switch off.....now checking all wiring related to this...
     
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  13. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    What do you mean by "tachometric relays"? There is only one tachometric relay (behind the fuse-relay panel) that runs the fuel pump relays. Or are you bridging the fuel pump relays?
     
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  14. turbo-joe

    turbo-joe F1 Veteran

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    why tachometric relays? there is only 1 inside. so have to ask also steve´s question again: you mean the fuel pump relais?

    or you mean this 1 tachometric relais not work rigth and so you jump both fuel pump relais?
     
  15. Dadster

    Dadster Rookie

    Sep 16, 2017
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    S Evans
    sorry yes...jump both fuel pump relays. the one tachometric relay appears not to work correctly...

    where do we get one for a reasonable price?
     
  16. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
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    at this tachometric relay there is a fuse. check if the fuse has good contact. because of vibration it could happen that it is not working right always.
    you may also open the relais ( take the inside out from the cover ) and check the contacts and if the spirng inside still is ok.
    mercedes has the same relais. it is from bosch. have the bosch number not in mind but you may read the number on the housing of the relias and then google a little.
    I not would buy a used one at ebay or somewhere else. you never know how long it was laying around and if it will work fine or not. except you will find one in your near what you could give back if not working

    unfortunatly you not filled out your prfole so I not know where you are located. I still have one in stock ( used one but working, put it out from my car when I put in other injection system ) at home and hopefully can go back from thailand on the 25th july
     
  17. Qavion

    Qavion F1 Veteran
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  18. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    You guys are confusing the Protection Relay (that has the fuse and is not a Bosch relay) with the fuel pump Tachometric Relay (which is a Bosch relay and has no fuse).

    I would make sure that the 7-12 bank is not losing spark (when above 3800 RPM) before buying a new tachometric relay. This would also (correctly) open a working tachometric relay (and turn off the fuel pump relays), and you may not detect losing a bank of ignition if you are testing with the jumped fuel pump relays at no engine load.


    Don't have a specific source. The Bosch PN is 0280230006, and others have posted that Durite 0-732-42 is an equivalent. It's your homework to search the web, and let us know where you get one if you need one ;)
     
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  19. Qavion

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  20. Dadster

    Dadster Rookie

    Sep 16, 2017
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    S Evans
    thanks for all the help.

    It turns out someone used the wrong relay in the past when they 'fixed' the car.

    Correct part is 124717 Tachometric relay. Bosch number is 0280 230 006. this seems to be the one you mention above.?
     
  21. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Yes, Bosch 0280230006 is the correct one for this use (and there are many other Bosch "tachometric relays" that operate at different RPMs and/or have different switching logic so not too surprising that someone got things confused).
     
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  22. Dadster

    Dadster Rookie

    Sep 16, 2017
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    S Evans
    bought a used bosch from ebay...

    car running well....just added capristo exhaust....sounds amazing
     
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