Engine/Transmission (1994 - 1998) Fuel pressure Problem

[biggy238]

First, let me say that my FP isn't too low.



I put my truck in 1st (automatic) to compression brake down a long hill to a river bottom.



When I installed my FP gauge it would idle at 31 and run at 28.



After running down that hill, The fuel pressure idles at anywhere from 35-55 psi and fluctuates and has now gotten to where when I let off the throttle to coast in traffic the psi will spike.



The highway speed FP is still around 28.



Is there something I need to check into or be worried about? It built up to 53psi last night sitting in line at McDonalds (gauge is set at 50psi warning so it got to flash the whole time). This is all on a filter with 1000 miles on it so it should be alright.



Thanks for any insight.

Kyle

 

[ABorchard]

Sounds like it's time to replace the overflow valve, the ball inside it is sometimes sticking in it's seat. I wouldn't wait long, with the pressures you're seeing you could possibly split the fuel filter open.

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Precision Diesel Injection and Turbo Inc.

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$35 + $7 shipping and handling.

 

[biggy238]

Thank You.



I knew it had to be something along those lines but I don't have enough experience to figure it out on my own.

I hope it's an easy install.



Thanks again.

 

[ABorchard]

Replacing the OF valve is a five minute one wrench job if you don't drop the sealing washers, stuff a rag under the valve to catch a falling washer. Remove the old valve and put new one in it's place. Occasionally the notch in the manifold you see to the left of the OF valve in the picture needs to be filed or ground a little to allow the old valve to be removed. Don't bend the line to remove the valve, it will make it very difficult to line up right again. New style OF valves don't always have the retainer on top that says not to remove, don't worry it's just a design change.



The object in the lower left corner is your oil fill cap.

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[biggy238]

Sweet, It gets better by the minute around here. Oo.



I remember A post a few months ago about split fuel filters. They blamed it on the filter manufacturer. I wonder if they met the same fate that mine is trying to deal me.



Again, Thanks for your help and time saved.

 

[biggy238]

O. k. now the fuel pressure has dropped. It hit 20 psi on a 3-4 shift and i almost choked myself when i saw it. I checked the fuel filter over and found no leaks or a rupture. I hope this valve really is the end of this problem.



Kyle

 

[ABorchard]

What you are seeing is pretty typical. What happens is one side of the ball wears in the seat and starts looking like a ball with a bump on it. Before the long the bump can get stuck in the seat = high fuel pressure. At other times the top of the bump can contact on the edge of the seat resulting in a poor seal = lower fp.

Most overflow valve springs get weak resulting in low fp long before the ball wears out.

I came across one a few years back where the ball had worn down so much that it finally passed though the seat and got stuck in one of the holes in the banjo bolt.