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

Tiny
CBPRIZM00
  • MEMBER
  • 1993 GEO PRIZM
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 205,000 MILES
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.
Monday, January 11th, 2010 AT 7:29 PM

1 Reply

Tiny
MMPRINCE4000
  • MECHANIC
  • 8,548 POSTS
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.
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Tuesday, January 12th, 2010 AT 6:53 AM

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