My uncle has a 1990 K1500 4x4 w/ 4.3

I has close to 300k on it. Starts fine, runs at idle but as you accelerate or put a load on it(especially up hill or getting on the gas...merging on the highway etc.) there is a steady knock.......it won't accelerate....gets up to speed but takes a long time.

Would this be timing or knock sensor? Truck vibrates a bit at idle....leads me to believe timing is off a bit. Timing chain has not been replaced.

Any ideas?

Thank you.

 

I had a "95" K1500 that had the same issue,found it to be the vacuum advance in the distributer was rusted and wouldnt allow the advance to work..

 

Thanks for the responce.....that's one we didn't think of....

 

your welcome!!