89 w150 w/318. When the key is moved to ON position there is no sound at all from the fuel pump to indicate it's priming. Truck cranks and fires right up sometimes, other times it will crank for 5 seconds or more before starting. Sometimes it will start then stall. It always fires up and stays running after it does stall. Any thoughts why?

 

I'm thinking it's not a fuel pump problem. Many pumps will become quiet once pressurized. Take a reading on what the fuel pump pressure is. You didn't mention tune-up. Are the plugs correct and newer? I've mentioned in the past that our shop was very strict on not using AC plugs at our dealership. I saw firsthand the problems AC plugs created.

 

I agree on putting a pressure gauge on it and seeing what the pressure reads are.....
Also, When was the last time the fuel filter was changed?

Keep us posted... Cheers

 

Are the power and ground correct or backwards? Are inlett and outlett correct or backwards? It doesn't pump even if the out is left disconnected