Starting problem W4500

OK, maybe you guys can help me out here. I have a 03 Isuzu NPR HD (W4500) with a GM 5.7 gas motor.

After the truck sits for any time longer than 20 mins, I have to crank it 6 or 7 times to start it. Once it starts it runs perfectly under all conditions. Fuel filter replaced, no change. I suspect it a fuel related problem. As if the fuel system is loosing its prime and it takes 6 cranks to re prime it.

Its in the shop now and they say its the fuel pump.. no question. Sounds reasonable, but the truck hauls ass pretty well for having a bad fuel pump. Quoted $500 parts and labor.

Any thoughts?

Sometimes the pressure check valve fails in the pump.
When this happens the fuel drains all the way back to the tank.
It causes long cranking because the fuel has to be pumped all the way from the tank to prime the system.

Sounds like a proper diagnosis, and price is also in the ballpark.
Are they using factory or aftermarket replacement parts?

Thanks Rabbler. Yes, based on what you are saying, the diagnosis does make sense now. I don't know if its a factory part, or even if the pump is Isuzu or GM. 4 days to get the part so Im guessing factory part. Im going to find out tho.

Updating an old post here... what a horrible experience this has turned into.

Back at the time of my original post, the fuel pump was replaced and a bad wire was found that was shorting out. This wire went from the fuse box to a relay (I believe it sent signal to the fuel pump to start) Apparently this was the route cause of the problem. All fixed.. truck runs great.

2 months later (last week) the truck will not start after sitting all night. Call the same shop, have it towed in. They take two days to look at it and say another wire has gone bad. Replaced wire (only charged me half hour labor) and told me to come get the truck.

I get there and its still in the shop...........:rolleyes: Truck will not run. Now I am pissed. They tell me they have to drop the tank to check the fuel pump and that possibly the connectors are bad. Will have that done after the holiday and THEN order new pump if necessary...

Sooo my conclusion to all this is... 1) my truck is shorting out fuel pumps and now they butchered my wiring. OR 2) They put in a cheap fuel pump last time and it just went bad. OR 3)They used some generic fuel pump and had to modify the Isuzu wiring.

If its a bad pump or bad connectors its under warranty.. But no truck for another week. I have to pay for the tow

Any additional thoughts on this????:confused: