I have an 88 Chevy Silverado 4x4 350 engine, auto trans. Truck ran fine now wont start. I replaced fuel pump, checked all fuses and replaced oil pump solenoid, still won't start. If I run a jump wire directly to the fuel pump it works fine but won't stop pumping fuel when I turn the key off. Is it possible the oil pump is bad? Maybe there's a fail safe if the truck shows no oil pressure? At a loss, need advise.

MC