this is my problem, i have an 89 gta 350,when i crank it, it won,t fire,but if i spit gas in the plenum then it fires up.but if i let it sit and try again it won't fire up,i measured the fuel pressure and it reads 42 psi but then it falls to 20psi after the pump stops,is this fuel pressure regulator problem or fuel pump,what can you advise, help is appreciated,gm hombre.

 

May be fuel pump relay.

 

I would check the injectors. Mine would do the same thing. It wouldnt start when it sat and if you shot starting fluid in it, it would start right up. Found four bad injectors. Replaced the injectors and it fixed it. The fuel drops seems really low to me. Could be a bad fuel pump.

 

fuel pump seems to me what it could be, but if the pump shoots to 42 psi and it doesn't hold wouldn't it be the fuel pressure regulator to hold pressure steady? i'm going to buy diods to check the injectors,maybe it is the injectors but i have to be certain,thanks gm hombre.