I have a Winnebago on a E-450 chassis, V10 engine. It is a 2002 with about 50K. It is hard to start, sometimes having to crank it a few times to get it to start. It will stumble as it cranks like it wants to start but can't. I have run injector cleaner and heat through it, I changed the fuel filter, (it has been happening for 7k miles so it's not bad gas), I just got done changing the spark plugs (yes i know about the head issues and plugs blowing out) and to no avail. I assume it is the fuel pressure so I checked the fuel pressure on the fuel rail. With the key in run, the rail hardly shows any pressure (like 2 psi if that). I start it and it goes to 30 psi and seems to hold steady there. I assumed it was the fuel pump, but decided to check my F-350 which also has the same engine and is practically the same age. It doesn't have any pressure in the rail when the key is in run either and it doesn't have any problems starting. I really don't want to drop the tank and change a pump just to see if it helps. Changing the plugs sucks, but the fuel pump sucks worse. So, should I be getting fuel pressure on the rail when the key is in run? What should the pressure be for both key on and engine running? Is there another fuel bypass valve or something like that, that could be causing this. This problem came up all of a suddenly about 7k miles ago. Before it had no issues starting at all. I can't say its getting worse, but it is definitely not getting better. Any advice would be greatly appreciated.

 

This s what you could try,
Get hold of a fuel pressure gauge and connect it to the schrader valve on the fuel rail.
When you first turn on the key the fuel pump relay should make the pump run for approx .2 seconds Then unless the computer receives an RPM signal from the crank sensor the relay will drop out. The RPM signal from the crank sensor goes to the computer and that keeps the fuel pump relay energized. With the key on and no rpm signal = no fuel.
When running , 35-45 psi. If all checks out, try this last check. After setting a few hours before turning the key to the start position , turn the key on then off a few times then see if it starts any faster. If it does, the check valve in the fuel pump module in the tank is not working and replacement of the complete module is the fix..

 

Thanks for the response. That is good info and helped a lot. I put a fuel pressure gauge on the fuel rail and if I turn the key on and off I can build the pressure up to about 20 psi, they I try to start it, and it starts right up. It just won't keep that pressure for more than a few seconds. I tried it on my truck and it holds the pressure without it going down at all. The .2 seconds fuel pump on and the check valve were not in my knowledge bank I now understand the system much better and it makes me feel better changing out the fuel pump knowing and not guessing it is the issue. It's nice to not have to pay a $1,000 for a $150 part. Now I just need to do it......