do i need a fuel pump?

[travis873o]

So my 740 will start just fine and idle as well. and is drivable but only for about the first 5 minutes. then it acts like it is not gettting enough fuel (starts to spudder, the throttle doesn't do anything but make it choke). I just put seafoam in the tank so this leads me to believe either my fuel pump or prepump (or both) are going.

So.

1. Can anyone confirm that this is a fuel pump issue?

2. If i replace the pump, I already have an MSD fuel pump that I could put in. But it is an inline pump. So would I have to bypass the prepump? or should i bypass the prepump? Also should I place it before or after the filter?

3. Would you all recommend the MSD pump vs. the stock setup? I may plan to run more boost in the future but nothing more than 15 psi.

any input would be great. Thanks.

[travis873o]

I've also just replaced the fuel filter.

[lummert]

The in-tank pump is needed to supply fuel to the main inline pump.

[travis873o]

you don't think the msd pump could pull the fuel from the tank?

[lummert]

In my experience the inline pumps are not designed to pull fuel, only pump fuel. Unless the manufacturer states that it can be used in the manner.

This is my experience with in-tank pumps and main in-line pumps. When the in-tank pump has failed the fuel in the tank will get heated because of the fuel returning from the hot fuel rail. The fuel in the tank gets hotter when the tank is less than half full. When the outside temp gets hot the main in-line pump will vapor lock which will eventually cause pump to fail. When the tank is full this symptom seems to not happen, but I've experienced vapor lock on a 95 degree F day with low humidity with the tank only down 5 gallons. Since replacing the in-tank pump I've managed to drive in 106 degree F temps with more than 225 miles on a tank of fuel.