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924guy · Posted: Mon May 15, 2006 3:27 am Post subject:

just a thought, but if youve got bad wires at the fuel pump, or pos battery term that are creating high resistance as they heat up, or even grounding, itll act like far worse issues.. electrical gremlins can really create a mess....
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Eric
78 924
82 931 SE "smokey"
99' VehiCross
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Smoothie · Posted: Mon May 15, 2006 4:49 am Post subject:

Eturbo924 first suggested weak spark caused by a bad coil, then seemed to take it back - but it should still be "on the table". Your symptoms - misfires under load, fit exactly with weak spark. Check the spark strength. Spark should be a bright blue or white and jump a distance of at least approx. 10mm and make a nice loud snapping sound. A thin yellow spark would be considered too weak. Spark is inhibited further under compression in the environment of a cylinder with its' fuel rich air and heat, so while it only needs to jump a very small gap on a spark plug, testing it out of the cylinder you see it jump a much larger gap if it's strong enough to perform in the compressed cylinder environment.
If you find the spark is in fact weak, but the charging system is ok, then the problem could be weak coil or other ignition component.

5 pics with comments starting here - http://pg.photos.yahoo.com/ph/smoothies931pics/detail?.dir=bdb3&.dnm=5548.jpg&.src=ph
You could make your own el'cheapo tester from an old plug wire - cut off the spark plug end connector, plug the other end into the dist cap, hold the wire end with insulated pliers over a ground point on the engine and see how far the spark jumps.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

seanski44 · Joined: 13 Mar 2006 Posts: 532 Location: Nottingham UK

just occurred to me that if its running rich and seems better when cold it could be running 'on choke' - I had this and it was bad earths, the cold start gear (WUR I guess) wasn't able to determine the engine temp and so when the car heated up, it would choke on too much fuel. clean all the electrical contacts etc...

again, good luck.
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1998 BMW Z3 2.8 arctic silver & red

1981 168HP 931 S2 blue/tan leather - SOLD

1985 121HP 924 2.0l na modded - SOLD!
1992 968 lux SOLD
1989 944 2.7 lux SOLD

BC77-924 · Posted: Tue May 16, 2006 11:18 am Post subject: Thanks for all the responses

I have left the car with a different mechanic for the next12 days or so. Hopefully the new guy will be able to sort things out.

D
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Silver/Grey 77.5

Ozzie · Posted: Tue May 16, 2006 2:39 pm Post subject:

Just a revision of my earlier post. The tank is slightly pressurised and the fuel cap should be sealed.
The tank is not at a high pressure - just a few psi.
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Porsche 924 1984 (UK import) NA
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