505 sti miss-fire and lag
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  1. #1
    Tadpole
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    Default 505 sti miss-fire and lag

    Hi,

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    So my automatic 84' sti has been having trouble with some sort of miss fire. Its happening from cold up till running temp but its at its worst just after start. It will only happen between idle and about 2500 rpm and when it does happen its a sudden loss of power and rough running but once accelerated to about 50km/h it disappears. On the highway she's still as smooth and comfortable as always. I've been through the haynes manual and had a look at all the advice on servicing injector and spark components but haven't had a look at the distributor yet. 2 of the 4 spark plugs had oil in the thread and were a little dirty and the other two didn't show any signs of oil and were a little cleaner. when the car is at idle and i put my hand on the distributor leads i can feel the spark on my fingers. Normal? The leads are relatively new good quality ones so they shouldn't be a problem.
    I noticed in the haynes manual it refers to the mixture screw and when i looked for mine its missing. The screw housing is still there but the screw is missing? could this be part of the problem or just another completely unrelated thing i'll have to fix?

    Now to the lag which is possibly related but most likely not as it has been happing for over a year now. Usually, but not restricted to cold starts, the car is extremely slow off the mark. It has nowhere near the usual amount of acceleration and power until you give it a few revs or get up to about 50-60km/h in 2nd gear when something miraculously kicks in and gives it its normal power. I can hear the external fuel pump running and know the car wont start when its not running so i've taken that off the short list of culprits. The top of the short list is the in-tank lifter pump. Could this be straining the external pump if its faulty and not running causing a lack of fuel flow?

    I can see this is all a jumble of info about the problem but im sure if anyone has experienced this or worked on a car with a similar problem they might be able to help.

    Thanks in advance

  2. #2
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    Quote Originally Posted by tdhalsall View Post
    Hi,

    So my automatic 84' sti has been having trouble with some sort of miss fire. Its happening from cold up till running temp but its at its worst just after start. It will only happen between idle and about 2500 rpm and when it does happen its a sudden loss of power and rough running but once accelerated to about 50km/h it disappears. On the highway she's still as smooth and comfortable as always. I've been through the haynes manual and had a look at all the advice on servicing injector and spark components but haven't had a look at the distributor yet. 2 of the 4 spark plugs had oil in the thread and were a little dirty and the other two didn't show any signs of oil and were a little cleaner. when the car is at idle and i put my hand on the distributor leads i can feel the spark on my fingers. Normal? The leads are relatively new good quality ones so they shouldn't be a problem.
    I noticed in the haynes manual it refers to the mixture screw and when i looked for mine its missing. The screw housing is still there but the screw is missing? could this be part of the problem or just another completely unrelated thing i'll have to fix?

    Now to the lag which is possibly related but most likely not as it has been happing for over a year now. Usually, but not restricted to cold starts, the car is extremely slow off the mark. It has nowhere near the usual amount of acceleration and power until you give it a few revs or get up to about 50-60km/h in 2nd gear when something miraculously kicks in and gives it its normal power. I can hear the external fuel pump running and know the car wont start when its not running so i've taken that off the short list of culprits. The top of the short list is the in-tank lifter pump. Could this be straining the external pump if its faulty and not running causing a lack of fuel flow?

    I can see this is all a jumble of info about the problem but im sure if anyone has experienced this or worked on a car with a similar problem they might be able to help.

    Thanks in advance
    Check that the large intake air connection on the Air flow Meter hasn't come come loose.

  3. #3
    Tadpole
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    Quote Originally Posted by GRAHAM WALLIS View Post
    Check that the large intake air connection on the Air flow Meter hasn't come come loose.
    sorry for my limited knowledge, where is the air flow meter?

  4. #4
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    Quote Originally Posted by tdhalsall View Post
    sorry for my limited knowledge, where is the air flow meter?
    Where the fuel injector pipes run from.

  5. #5
    Tadpole
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    Ok i'll have a look tomorrow and let you know how it goes.
    Thanks graham

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