1999 Silverado 5.3. One day its starting/running fine, the next day it turns over but won't start. Find the fuel pressure around 5lbs low. I pull the vac hose off the regulator and it jumps to around 58 psi. I pull the vac hose and clamp the return fuel line and it jumps to 90psi

I replace the fuel pressure regulator and fuel filter. Still get same symptoms. At this point I try starting with starting fluid, which it does and runs really rough. I can shut it off and start it when its warm at this point also.

Next I replace the fuel pump using an AC Delco pump. Still getting same symptoms. Low pressure and runs horrible.

So now my head is full of question marks. Could the pump not be getting enough power? Could I have a leaky injector?

I can test for spark but that would not account for the low fuel pressure.

 

Do you have a check engine light?

 

No check engine light. I just confirmed today that it will start cold now. Before the pump install I would have to use starting fluid. Now it runs like its getting a misfire, but no check engine light yet. Maybe I haven't let it run long enough to let the light come on.