Hello, I have a 1990 K2500 5.7. So a while back the engine started knocking under load. It originally started around the same time I changed a leaking radiator. Later I found one of the oil ports in the radiator was mostly clogged so I changed it again. Throughout this time this knocking has been driving me crazy. It idles ruff has a miss at all rpms and knocks under load and at low rpms the engine cuts out for a second and bucks and carries on then takes back off. Once in a while when going down the road it all just clears right up for a few seconds and all the power and everything comes back then goes back to missing. It's had a tune up with plugs, wires, distributor, knock sensor, coil, oil pressure sending unit, and oil. I have checked the egr valve with vacuum and as soon as I start to put vacuum to it with the engine running it stalls. I've tried high octane fuel with no help. I've tried the timing all over the place and with it set to 0 I can kind of limp it around. This evening when I get back home I'm going to check fuel pressure but pretty much I don't know where else to look.

 

I'm having the same type of issues as DD, rough idle, stumbles and misses under acceleration, pings when gaining speed. Gets better as I let off the throttle, and acts fine at steady, level speed. Same truck, 1990 k1500 5.7. Neighbor, who is the local mechanical whizard, first response was bad cat. This has the cat delete, previous owner was on a farm and given the age, there was no reason to replace the cat. His next guess is the EGR valve, which I will replace in the morning. When I bought this truck in July, he had just cut the exhaust off as the muffler had rotted out, I put on a stock, quiet, cheap muffler to keep quiet around town. If not the EGR, is it possible the muffler is too restrictive?

My 1988 also has the cat delete, have never had this issue with that truck.

Any ideas might help both of us get our trucks feeling better.

 

I ended up doing a compression test and the number 4 and 6 cylinders only had 30psi compression, so it's getting a engine overhaul or new engine whatever ends up happening