Engine/Transmission (1994 - 1998) Fuel Pressure and Overflow valve

[Hirt]

I know this topic has been covered quite a bit from all the replies I am getting from searching, but just wanted some input. I installed a fuel pressure gauge yesterday since I have been in question as to whether I am getting normal pressure at higher engine speeds. It turns out that at idle I was around 17 psi and at 2500 rpm not much more (no load). I took apart the overlow valve and checked the spring which was about 7/16 so I got it to a hair over 0. 5 and tried it again. Fuel pressure at idle was about 24 psi and at 2500 rpm it was about 20-22 psi. I took it for a test drive and it seemed like it helped but it is very easy to get the fuel pressure down to almost 0 psi. I should have mentioned before stretching the spring I was only getting about 22-24 psi boost and after stretching I was able to get back to about 30 psi boost. I was going to order an overflow valve tomorrow but I guess I was looking for some input as to whether everyone thinks this will solve the problem. It leaves it a little in question for me since I now know the spring is about where it should be and my fuel pressure is so low. My sig has the information on the truck and I should note that the TST plate is set in the same place as the stock one. No fuel leaks, very slight seeping has started around some hoses but nothing that would cause such low pressure. Any input would be appreciated, thanks in advance.

 

[Hirt]

Anybody???

 

[ata]

Your fuel pressure should be 18 to 22 idle 24 to 28 at 2500 no load and should not drop below 18 full load and this is with warm fuel, cold fuel should be higher. With it droping to 0 sounds like bad lift pump. Clamp the return line and it should peg the gauge if not bad lift pump.

 

[CCiatteo]

I had the same issues you mention. My idle fuel pressure was low, hovering around 0-5psi and my pressure under load would rarely get above 15-20 at its peak. I swapped out a new lift pump and did the overflow at the same time (from Tork Technology) and now my idle pressure is 20-22 and pressure under load it 38-42psi.

 

[Hirt]

Thanks for the replies so far. I should have mentioned I did try pinching the return line and while running at 2000 rpm the fuel pressure did increase. I just put some pressure on the hose not really pinching. Kind of scared I would damage the hose. Seeing this increase it does lead me to the overflow valve however as mentioned while under load it is easy to get down to 0 psi which then leads me to wonder if the overflow valve is really the problem and not the lift pump or maybe both.

 

[Missouri Mule]

Hirt, in 96 FSm it states that lift punmp should deliver fuel to fuel filter and p7100 at 25 psi(at idle). You have 5 psi max drop before fuel filter and after fuel filter( so you should have no less then 20 psi going to P7100).



When you squeeze(hard with pliers) return line if pressure goes up the probelm is the overflow valve, if does not goes up or goes up slowly it is the lift/tranfer pump. (This is if your pressure is low at idle. )



When you rev your engine pressure should go up. Pressure varies with engine rpm.



Is your truck hard to start?

 

[Hirt]

The truck is not hard to start at all. I did have to apply some throttle however I recently adjusted the idle (was a little low) and now it starts easily without any problems.

 

[GOTSOOT]

get both the overflow valve and fuel pressure snubber from Robert @ torktech!!!! the difference is night and day!

 

[CToney]

Overflow valves from Tork Technology work great. I put one on a tractor with 8. 3L Cummins and going up hills I used to have to downshift a lot now no shifting. The govenor works properly now. I must have gained 40hp. It had the pressed in ball overflow valve, I guess those ones are really poor. Don't hesitate just put one on.