This is a long post, so please bear with me!
Details
1992 C1500 5.7/MG5
Originally a 4.3 now a 5.7 (I did the swap, have had the truck since 1998, 323K on the original 4.3 and it still wasn't dead!)
The 5.7 has a claimed 96K miles on it and is a roller cam 5.7 from a Caprice.
I did this swap as best as I could. I wanted it to look and act factory, so it has the correct ECU, prom, injectors, and other misc. No headers, stock manifolds, full exhaust and O2. It does not have a converter.
I have a rough idle, stumble under load, and I believe a misfire somewhere.
Driving in gears 1-3 are bearable but in 4 and 5 there is little power and the truck surges, stumbles, and shakes awful. Those gears are almost unusable.
Already checked/changed
Did a compression test, all cylinders and they were consistent at 190psi. Seems like most compression tests should yield around 150 psi. Could this be an issue?
I've tried 2 different distributors. One was new from Car Quest, the other was the original from the 5.7. The original one worked a lot better and cleared up some issues.
It has a new cap and rotor on it now, it doesn't look like it is arcing, and the wires are good.
Timing is set at 0*, new timing chain and it was installed correctly.
Re-set valve lash while the engine was running with a 3/4 turn.
There was little to no carbon build-up on the cylinders when I took the heads off. Heads were good, no cracks.
New fuel filter, fuel pump works great. It's not a fueling issue.
Most important: NO CODES! So that doesn't even help.
The ECU is checked and working properly.
At a loss here, I cannot think of what else it could be.
Details
1992 C1500 5.7/MG5
Originally a 4.3 now a 5.7 (I did the swap, have had the truck since 1998, 323K on the original 4.3 and it still wasn't dead!)
The 5.7 has a claimed 96K miles on it and is a roller cam 5.7 from a Caprice.
I did this swap as best as I could. I wanted it to look and act factory, so it has the correct ECU, prom, injectors, and other misc. No headers, stock manifolds, full exhaust and O2. It does not have a converter.
I have a rough idle, stumble under load, and I believe a misfire somewhere.
Driving in gears 1-3 are bearable but in 4 and 5 there is little power and the truck surges, stumbles, and shakes awful. Those gears are almost unusable.
Already checked/changed
Did a compression test, all cylinders and they were consistent at 190psi. Seems like most compression tests should yield around 150 psi. Could this be an issue?
I've tried 2 different distributors. One was new from Car Quest, the other was the original from the 5.7. The original one worked a lot better and cleared up some issues.
It has a new cap and rotor on it now, it doesn't look like it is arcing, and the wires are good.
Timing is set at 0*, new timing chain and it was installed correctly.
Re-set valve lash while the engine was running with a 3/4 turn.
There was little to no carbon build-up on the cylinders when I took the heads off. Heads were good, no cracks.
New fuel filter, fuel pump works great. It's not a fueling issue.
Most important: NO CODES! So that doesn't even help.
The ECU is checked and working properly.
At a loss here, I cannot think of what else it could be.