walexa

For the 94-early 98 dodge cummins with p7100:

My truck came with its original overflow valve. Upon recommendation that it is one of the first things to go (get weak) I replaced it with a new one. The old one could be disassembled, and has a spring and ball in it. I had taken mine apart, but just put it back together and threw it in a drawer. I have replaced it twice in the last 110k miles.

I recently installed a fuel pressure gauge. To my surprise it was always running at 20psi. I pinched off the return line from the IP and it would increase. So, I knew it was the overflow valve. Also, pump psi should change with rpm, but it always hovered between 20-22. I didn't want it to be 45 but felt it should be higher and at least fluctuate with rpm.

So into the shop I went and dug out my original overflow valve. Took it apart and noticed some shims that compress the spring........these shims were on a stem that is part of the bolt that threads into the valve assembly. I have read that no one (infidel) was able to source a replacement spring to increase the pressure, and some have stretched the spring to increase the pressure for alittle while, but it would always end up dropping back down to the lower pressure. So I decided to make a shim.........I used a dremel tool with a cutoff wheel and trimmed the end off of a 5/16" tee.........probably 30 thousands. It fit perfectly and now my pressure ranges from 30psi to 38psi. Not sure what it should be, but I felt it should be higher than 20. Hope this helps someone else out.

Waylan

infidel

Good job Waylan but I don't think it will work for long.
My experence is the spring loses it springiness over time probably due to engine heat. Seems to lose springiness faster as time passes.
Guess you could just keep adding shims though...

Txwelder

Im surprised that a more efficient pressure regulation device has not been created to replace the stock overflow valve.

GAmes

I'm surprised he has had to change it so many times. I've replaced mine once, and that was prolly 350k ago.

kawi600

I stretched the spring in my overflow valve to 1/2" (I think.. or was it 12mm?) and I get a consistent 28psi idle, which is on the high side of just about right.
I bought the original cummins part and it had what looked like adjustment shims.

walexa

I have not "had" to change mine out. I bought the truck with 95k on it and replaced it pretty soon as I had read that it was one of the most common problems on that vintage cummins. I bought the replacement from marty thompkins. Now that I have passed 200k, I was reading here on DTR and someone posted bosch overflow valves for $20 on ebay, so I bought one and decided to go ahead and install it as preventative maintenance. Then I added a fuel pressure gauge and it always hung around 20psi, thus my adventure to increase it a little.

I was watching it last night and warmed up at idle it is around 28, and goes up to 36-38, depending on rpm and engine load.

Waylan

kawi600

those readings sound exactly like what I have. its always 28 at idle and goes as high as 35 at 2krpm no load.