1993 Geo Prizm 1993 Prizm (1.8 lt) misfires when warmed up

1993 GEO PRIZM
205,000 MILES • 4 CYL • FWD • AUTOMATIC
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CBPRIZM00
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Noticed a whirring noise from the engine (sounded metallic - like a loose part vibrating at a very high frequency). Sound appears to be internal. Knew something bad was happening and planned to get it in for an engine check. Otherwise engine was operating OK. Problem developed a misfire symptom that can't be ignored. When car is started, seems to idle OK - no misfire. Once engine begins warming up, misfire begins. I tried new cap/rotor, but not getting off that easy. I haven't checked the plug wires (they are just 1 year old), but seems like it wouldn't be tied to engine temp. I'm thinking mechanical issue with distributer, but they cost ~$200 for a a good rebuilt and hate to experiment at those prices. Whirring noise frequency does seem to be tied to RPM (more RPMs faster whirring) and seems to stop for a microsec at when the misfire occurs (but that could also be my imagination). Other possibilities running thru my head are timing belt idler or valve/lifter.
Jan 11, 2010 at 7:29 PM
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MMPRINCE4000
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I would remove valve cover and check lifters/shim clearence, inspect camshaft lobes for unusual wear.
Shim clearence on a cold engine should be .008 intake and .010 exhaust.

You can also check timing belt with cam cover off.
Rotate engine by hand to look at the entire timing belt.

Try a junk yard for a used distributor, 93 Prizm or Corolla.

Generally either the coil or ignitor can go bad in the dist.
Jan 12, 2010 at 6:53 AM
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