I have a '99 E-350 6.8L. Where is the check valve that maintains fuel pressure on the system?

I have been experiencing a starting issue when the engine is hot. Cold starts are usually fine. I've replaced the in-tank fuel pump (pump only, not the assembly) to no avail. I was out of town and didn't have access to a fuel pressure gauge when the problem started so I couldn't say what I had prior to replacing the pump. But now, with a new pump, when I check pressure, I get about 40 psi when I first cycle the key on, but it drops right back to zero as soon as the pump shuts off. If I cycle the key on a few times, sometimes I can get it to hold pressure at about 32 psi, and it starts fine. When I shut if off, it goes back to zero psi, sometimes gradually, like a bleed down, and sometimes immediately.

My conclusion from this was that the check valve was bad. I was told it was part of the in tank fuel pump assembly. Since I didn't replace the entire assembly, this made sense. So I just dropped the tank back down, but I don't see anything as part of the pump assembly that serves as a check valve. There is a rubber nipple on the end of the return line, but I don't see how that can hold any significant pressure.

So, before I go out and spend another couple hundred bucks on the complete fuel pump assembly, which apparently can't be purchased without the actual pump, I thought I'd ask. Where is the check valve that holds the pressure in the fuel system?

BTW, I also have replaced the fuel rail pressure regulator, but it made no difference (I went there first since that was much easier than dropping the fuel tank a second time).

 

In following the fuel supply and return lines along the frame rail and up to the engine, other than the fuel filter, I don't see anything inline that could possibly regulate pressure or flow. Both lines go up to the injector rail on the back of the engine where the regulator is. I can only conclude that the pressure check valve (or whatever regulates/maintains it) has to be located there.

I've replaced the regulator with a used one from a donor vehicle and it made no difference. While I wouldn't exclude the possibility that the used one has the same problem, I'd find it highly unlikely. If necessary, I can pull one off of a good running vehicle to verify. But, assuming that the regulator is not the problem, what else could it be??

 

the check valve is inside the fuel pump if it is bleeding off then you have a bum unit go get another pump test it before you put it in so you do not go though all this again if you find that is the issue . unless you have a leak of some sort or fuel transfer issue. do you still have a fuel pressure gauge at hand it will save lots of time. i do not have much faith that the pump is your issue. just because you got get new parts on it do not in any way mean they work i find if you get enough parts you also get some defective parts especially used junk yard units. do not waste your money you need to isolate the problem to one area if you find it is the pump good if you find its anything else then fix it i would bet 200 buck that your 200 bucks will have bought you a big pain in the rear.

 

I've reached the same conclusion. I was thinking that there was a check valve in the return line that held pressure in the system, but I believe now that function is controlled by the FPR. I understand now that my problem is likely that the pressure is bleeding back down through the supply/pump side of the system. The pump that I installed was an Airtex, and I've not heard good reports on their quality (I was broken down and out of town and AutoZone was the only parts store open that late and Airtex was all that they had in stock, or I would have installed a Delphi or Bosch). I have a Delphi ordered and will pick it up tomorrow and install it along with a new FPR, and hopefully I will be done with this problem. I will report what happens.

Thanks for the input!

 

i do not think a new pump will fix the issue do you have the tank down at the moment.

 

Yes, the tank is down.

 

check your fuel pressure at the pump it self.

 

How would I do that with the tank removed?

 

this may seem stupid but hook the pump back up lines and connection and tee in you fuel pressure gauge right as close to the pump as possible on the line going to the engine and turn the pump on and see if pressure still bleeds off if it does then you can say the problem is were you are looking if pressure hold then you know the problem is else were. i understand the tank is down but as long as the pump has fuel to do the test it would be worth your time.

 

I guess the OP must've given up and hauled his van to the wrecker. Or maybe replacing the fuel pump actually worked??!?!?
I'm having the same problem and it seems like no one in the history of automotive forum posts ever POSTS THE FIX in clear, simple English.