89 GMC 5.7L not running right . . . I'm stumped
The truck is a 1989 GMC 4x4 5.7L engine. It has about 69,000 miles on it. All original. It was bought brand new in Juneau, Alaska, which is landlocked hence the low miles for the age.
I bought the truck about two years ago. At that time it has a problem the previous owner, and a few mechanics couldn't figure out.
So, you could drive the truck so long as you accelerated very slowly (and I mean VERY slowly). It took many revolutions of the engine before it would fire off (but always would).
Someone recommended the MAP sensor. I replaced this and there was a definit improvement. You could feel more power it seemed, but only sometimes. The other times it would stumble and hesitate, and I was back to very slow acceleration.
The whole time, based on the symptoms, I suspected the ECT (engine coolant temp sensor). It ohmed out within spec. So I ruled it out.
That was a mistake! It turns out I think the ECT was ok, but the connection between it and the wire harness was NOT. Replaced pigtail and ECT and now the truck has no check engine lights or codes.
BUT, the truck still has something wrong with it. You still have to accelerate slowly or it will run rough.
I don't know what else to do, please help.
The town the truck is in has only 300 people, and no mechanics, you have to fix your own stuff . . .