Any help appreciated


Junior Member
Hi all, new to the site, and new GMC owner. I have never owned a GMC before, always Fords, so I dont know much about em.

The question is: I got the truck home today, bought it off an 88 year old man.
it is an '87 Sierra Classic 1500 5.7 2 bbl T.B.I.
It runs great under acceleration and upper R.P.M driving, but when I hit 45 miles an our and maintain that speed it has a bad miss all the way up to 50 miles an hour cruising, any slower it does not miss, any faster it does not miss.
I replaced the fuel filter and checked the spark plugs, they are fine. I thought it might be the fuel pump, but then figured it would get worse as engine speed increased. The old man did not drive it very often, when he did, probably like a snail.
The exhaust is not puffing very hard, could it be a clogged catalytic converter??
It has got me baffled, I will check the ignition timing tomorrow, but I doubt thats it.
Any ideas??

Alan Addict
I had something very similar on an 88 4.3L. Turned out to be worn bushings in the distributor that were letting the shaft move around and mess up clearances on the electronics that sense when to send the spark. A rebuild on the distributor cured the problem. It would only show up at part throttle and certain speeds. In that case it was right around 35 mph and felt like the truck was stubbing it's toe occasionaly.

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