Mechanics

MISFIRE

1988 GMC Van

Engine Mechanical problem
1988 GMC Van 6 cyl Two Wheel Drive Automatic 102, 00 miles

My 1988 GMC 1500 Vandura Van acts like it is misfiring. It was running quite badly a couple of months ago then one day it quit on the highway. I have replaced the fuel pump, relay, spark plugs and tested the wiring all the way from the fuel pump to the relay. I did have a bad ground which I fixed. Now it starts and idles fine and runs OK at low speed. But when running above 35 mph or when accelerating, it spits and sputters like a misfire and the MPG has dropped way down. I checked the injectors with engine running and there is a perfect cone of gas flowing. The 'check engine light' does not come on. Any ideas you have on what is causing it to run so rough would be greatly appreciated.
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JSH62
December 18, 2009.



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