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'89 GMC 4.3 engine missing sometimes

Hi,

My GMC Sierra 4.3 litre 5sp has just over 110k on it. Has always run well. Now the fast idle is really fast, but settles down to normal once it warms up. Lately, however, after about 15min at highway speed it starts "missing" or "bucking."

It's not gas as I've filled up several times at different places since it started. Could be plugs or wires / cap although all are only six months old and why would it only happen after driving for a while?

The only other thing I did was change the thermostat and coolant. I put in a 150 instead of 180 thermostat.

Thanks in advance, MZ

Reply to
MZ
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Put the correct thermostat in the engine. The correct one is 192 degrees. Your engine is never warming up as far as the ECM is concerned and running way rich, and probably fouling plugs if I were to make a guess. You can't randomly decide to change things like this on fuel injected engines, this isn't 1966 any more.

Whitelightning

Reply to
Whitelightning

yep as white says put the correct thermostat and your problem should go away

Reply to
tudysmuck

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