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I have a 1997 Subaru Impreza GX auto sedan. I have had an intermittent problem for the last year. Somtimes when the car is cold the engine cranks but does not fire. It never does it when the car is warm. If I leave it for a few hours it usually starts. Once started I never have the problem for the rest of the day. Subaru dealerships and specialists have been unable to detect the problem. Computer codes always show everything is ok. The mechanics have established that when the problem occurs there is definatley no spark. Numerous parts have been tried but to no avail. A friend told me that he had a smilar problem on his Kia (although his does not even crank when it happens). He was told by a mechanic that sometimes the "diodes" play up and that he should disconnect his positive battery lead and earth it to the car, then put the lead back on the battery. My friend insists it works every time. The last 2 times my Subaru would not fire I tried this and it turned out to be successful, the car started 1st time. What I would like to know is where is this "diode" likely to be located and also why this should work?

 

I am at a loss as to understand the rationale behind this "fix". I really would appreciate an explanation for this so that I can go back to the Subaru specialists and explain it to them and hopefully come up with a permanent fix for it.

 

Thank You

 

John Calder

john.calder@bluescopesteel.com

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In the Air Force, we call this FM - frikkin' magic, or something very similar to that.

 

The only diodes I know of that he may be talking about are the rectifryers in the alternator.

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I doubt that this problem is due to a diode. Doing a power fail reset type action like that is not normally associated as a fix for a diode problem. Diodes either work or they are bad. Electrolytic capacitors are more prone to that kind of fix, or a microprocessor circuit. These type of components and circuits will be found in the ECU. I would try changing that first to see if that helps. Since they are expensive you might want to try finding a used one from a salvage yard.

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Thanks for that. I stated that twice I had earthed the positive and reconnected the battery and it worked, unfortunately the last time the engine did not start, this "fix" did not work, so at the time of writing the car is sitting in my garage at home. Given that it now seems a coincidence that the car started when I tried the so called "fix" do you think that this problem still originated from the ECU? I dont mind getting a ECU (a refurbished one costs approx $500 in australia) but if you can think of any other sources for this fault I would galdly like to hear them.

 

Thanks once again

 

John Calder

 

I doubt that this problem is due to a diode. Doing a power fail reset type action like that is not normally associated as a fix for a diode problem. Diodes either work or they are bad. Electrolytic capacitors are more prone to that kind of fix, or a microprocessor circuit. These type of components and circuits will be found in the ECU. I would try changing that first to see if that helps. Since they are expensive you might want to try finding a used one from a salvage yard.

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Thanks for that. I stated that twice I had earthed the positive and reconnected the battery and it worked, unfortunately the last time the engine did not start, this "fix" did not work, so at the time of writing the car is sitting in my garage at home. Given that it now seems a coincidence that the car started when I tried the so called "fix" do you think that this problem still originated from the ECU? I dont mind getting a ECU (a refurbished one costs approx $500 in australia) but if you can think of any other sources for this fault I would galdly like to hear them.

 

Thanks once again

 

John Calder

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Had a similiar problem...... kind of. I'm sure this has been done, but, make sure the spark plugs are seated properly and check the wires. It took me a while but this what I found to be my intermittent problem with starting and idling, usually happened when the car was cold too.

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Your wondering if the ECU could still be at fault and the answer is yes. I would first try to make sure that voltage is getting to the ignition system before replacing the ECU and if you do replace it I would hope you could find a used one for under $100 from a salvage yard. The ECU may be the problem but I would really try to prove it before replacing it. I would recommend you purchase a factory service manual for the wiring of the car so you could check suspected areas if you want to try and fix this yourself. The problem may also be a simple wire connector that is making poor contact when cold. I would hate to see you spend a lot of money on parts and find out later it was something like that causing the problem.

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