Supra Misfire Problem

I am having an engine misfire problem on a 86.5 Supra w/ 7mge engine. It will start and run fine when cold but as it warms up I get a misfire on the #6 cylinder. I have changed plugs and plug wires with the same result. In testing, if I swap 2 plugs (even while warm) it will run fine for a few minutes until the #6 begins to misfire again. Any ideas??

Reply to
Todd Caddel
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What makes you think it's misfiring?...what are the symptoms?

Reply to
Gord Beaman

It develops a noticable miss after it warms up. When it is missing, I can pull the #6 spark plug wire off of the distributor cap and there is no difference in how it runs. However, when it is cold (and running fine) if I pull off the #6 wire it obviously will miss. I have changed the coil with another one I have and get the same symptoms. Any ideas??

Thanks, Todd snipped-for-privacy@airmail.net

Reply to
Todd Caddel

Look here:

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This is for a '90, but I don't think there's all that much difference.

According to the diagram, the 7M-GE has a distributor. You didn't mention anything about checking the distributor (the turbo is totally electronic, according to this diagram...).

I would suspect, ESPECIALLY if it has an aftermarket cap and rotor, that the tolerance on the 6th contact is changing either due to poor maunfacturing, perhaps thinner material near this contact, or a crack that expands when the engine produces enough heat. I would pull it and check it, start the engine, warm it up and check it again. Also check the cap and rotor for pitting of the contacts, etc.

I have come to not use anything but Toyta tune up parts on my 'good' cars. On the Celica I used aftermarket parts with no problem, but I have had a LOT of issues using aftermarket tune-up pieces on other models.

I have an '88 and it has a ditributor, cap and rotor.

Reply to
hachiroku

An easy check is to wait until it is pitch dark. Then fire up the engine with the hood up. Let it warm up & settle down.

Then take a look for any electic sparks jumping around near the ignition components when you rev the engine. Sometimes this is a giveaway for your problem.

Reply to
David J

Ever think that it might not be ignition at all?...could be that a valve is sticking open when the engine gets warm...

Reply to
Gord Beaman

Yeah, but it's easier to eliminate the stuff you can 'see'...

Reply to
hachiroku

True...but I thought that he had changed all items in the ign path to that cyl?...

Reply to
Gord Beaman

I don't thnk he mentioed the cap and rotor, or. if he did change them, if he used OEM. I got stuck by the side of the road in an Ice storm in Hartfors 'cause I used a Philko cap and rotor on my '80 Corolla. Luckily, a parts guy going back to the dealer saw the car and told the service manager, who agreed to leave the OEM parts with a salesman after hours. Thirty minutes later (INCLUDING the parts swap) I was on my way, NEVER to have trouble again!

The service guy said, "look in the top of the ditributor. See if there aren't little brass balls" Sure enough...the gap on the aftermarket parts was too large an it melted the contact end of the rotor, and one of the contacts on the cap was half gone and BLACK!

Reply to
hachiroku

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