[cdadkns]

I am working on a 2000 Four Winds camper on a Chevrolet chassis. It has a 7.4L Vortex engine with port fuel injection, same as the Silverado. The fuel pressure drops below 20 psi after the engine warms up and when under a load such as climbing a hill. The engine does not completely cut off. When you let up on the throttle, the fuel rail pressure immediately recovers to 52 psi. A local repair shop recently replaced the fuel pump which did not resolve the problem. During my troubleshooting, I found the fuel rail pressure regulator was leaking fuel out of the vacuum port, so I replaced it with a new one. This helped with the fuel pressure as now it climbs to near 60 psi when snapping the throttle. Once the problem occurs, you can snap the throttle to high idle and watch the fuel pressure drop, the engine will run, but lope near the hi idle pedal position. The longer you hold it there, the more the pressure drops until the engine finally dies out. As stated before, you can let off the throttle and the fuel pressure recovers to 52 psi. You can cycle the key switch off and restart the engine, the problem goes away until after 5 min running, then returns. I have replaced the fuel pump relay. I installed a test lead in the output side of the relay to ensure that when the pump acts up, the supply to the pump is 12 volts engine off and 14 volts with the engine running. This seems like an electrical problem due to cycling the key off and on, the problem goes away, the comes back after 5 min. Acts like something electrical is overheating. Has anyone seen this before? I would appreciate any help you can give!

 

[GMT604]

Replaced the filter? When they replaced the pump did they use ACDelco? Aftermarket pumps are garbage. Did they use the new revision connector that comes with the good pumps, and did they wire it correctly? There are two ground wires in the harness, the heavier one is the pump ground, the lighter gauge one is the signal ground to the PCM for the level sensor. If you mix them up all kinds of bad things can happen, as the signal ground will not handle the current draw of the pump properly.

 

[cdadkns]

Yes, the filter was replaced and I double checked to to be sure there is no trash in the tank that has plugged it again. It is clean and getting full flow out of it. I don't know any details about what the repair shop did. Not sure what type of pump they used. I am suspecting the new pump, but hate to drop the tank before elimination all other possibilities. I was thinking they may have not wired the pump correctly, so I will plan on dropping the tank to check. Thanks for your quick reply and good info!