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Posted by KevinD [Email] (more from KevinD) on Tue, 7 May 2002 17:21:56 Share Post by Email
In Reply to: '86 900S air flow sensor diagnostic tips sought, kansas, Mon, 6 May 2002 21:46:48
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By disconnecting the AMM electrical plug. If the engine runs better without the AMM connected that's a good indication the AMM is on its way out. You should also have an adjustable OHM screw on the electrical plug side of the AMM. Try dialing up the ohm resistance and see if that makes any difference to the cold start situation.

Diagnostic tests on the AMM can be tricky. Have you unhooked the air cleaner bellows and checked the AMM platinum wire to see if it "burns off" when you rev to 2500 RPM then shut engine off. A positive test there can be inconclusive as well.

Best test is to swap in a known good AMM and see if engine starts and runs normal. Have you checked all vac lines for splits or breaks? The Townsend site has a good narrative on cold start issues for this era engine. You may have another issue going on but it sounds like the AMM is the culprit. You may have to spring for a new unit ($130 Sobstory-site sponsor) or go the used route on E-bay. However, used AMM’s are the luck of the draw and may already be bad.

Another fix I’ve recently tried with my ’86 900T that had the cold start blues like yours was to wire in a 680 ohm resister in the yellow wire that goes into the NTC sensor on top of the engine. That ‘fools’ the fuel computer into thinking the engine is colder than it really is and richens the fuel mix at startup. That was a cheap fix (99 cents) that has worked well with me. You might want to give it a try before ordering a new AMM. Good luck.


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