Engine Performance problem
1997 Chevy Truck V8 Two Wheel Drive Automatic 152000 miles
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The engines runs really rough, the plugs in the 5, 6, 7 & 8 cylinders are fouled out. The compression in those cylinders is between 140 and 180. The cylinders are all firing. New cap, rotor, coil, plugs and wires. Problem stil exists.

Any ideas?

Plugs fouled out with what oil or fuel?

Plugs are black, but dry. Possibly fuel; not oil.

Well injectors must be leaking ie. dirty You can have them cleaned to verefy hookup pressure gague run tthen stop observe gague if is does not and starts to fall leaking injectors.
Good luck