505 STI misbehaving when warm
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  1. #1
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    Default 505 STI misbehaving when warm

    My 505 STI is running unevenly when warm, 'missing' particularly when accelerating. I runs perfectly for the first ten or fifteen minutes, but once warm the trouble begins. Even when warm, it idles well. I know nothing about fuel injection. Could any forum members suggest what I should check please?

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  2. #2
    Fellow Frogger! Molerpa's Avatar
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    If I am not wrong, was a post about this (same topic I think also)

    Is it an XN6 or ZEJ/ZDJ? K or L?


    Quote Originally Posted by luthier View Post
    It is simply impractical to expect a petrol motor to get through too much water. That's why God invented diesels.

  3. #3
    1000+ Posts jo proffi's Avatar
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    If temp is a trigger to poor running, it may well be the coolant temp sensor that is lousy.
    I've seen my similar vintage renix zECU default to 60 degrees when the (coolant temp) sensor is unplugged.

    I dont know exactly how you check the sensors, but diagnostic computers are always the best tool to use as they allow you test the whole circuit, not just the sensor.


    Jo

  4. #4
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    Try all the hoses. They may look Ok but, if old, may have cracks in them.
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  5. #5
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    Default most likely cause

    A careful check of all hoses did not indicate any leaks. What I did discover was that there was an arc across both the low-tension terminals on the coil . The problem persisted after the coil was exchanged for a new one. Once the engine is warm the ‘click’ of the arc is audible. When cold a faint spark is visible when looking at the terminals in darkness, even though the car runs and accelerates perfectly until it warms up. What are members' thoughts on this?

  6. #6
    Fellow Frogger! julian b's Avatar
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    I had a similar problem with my 504 ti motor and thought it was injection related ,but after replacing the spark plug insulators ,leads and condensor ,[everything else in ignition system was new] it ran perfectly hot or cold

  7. #7
    1000+ Posts Beano's Avatar
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    I agree. Electronic ignition coils put out more spark than the older style coils, and spark plug insulators are the first place I'd suspect arcing. Then leads. You could try looking at everything at night....
    As for why it might do it when warm, I guess even plastic and bakelite expand when warm.

  8. #8
    1000+ Posts Capago's Avatar
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    Quote Originally Posted by PCole View Post
    My 505 STI is running unevenly when warm, 'missing' particularly when accelerating
    someone who understands my/has similar frustration
    The wrong oil is better than no oil at all.

  9. #9
    Fellow Frogger! stew's Avatar
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    And so! Seems that the spark is reluctant to leave the coil, yes? That means big resistance either from leads, spark plugs, dist cap to rotor clearance and some times the carbon brush to the rotor has burnt away after being stuck. Air leaks around injectors and hoses? Just plain old stuffed ignition leads?

  10. #10
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    Thanks everyone. New leads, distributor cap and rotor seem to have rectified the problem.

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