Buzz'nhalfdozen

Hey fella's i've got a truck thats got me stumped. Its my buddy's truck. a 98 3500 with 4k gov springs, a 3 piece exhaust manifold, BHAF, and swapped the fuel filter for a 96 spin on style 5 speed and thats it. we just put boost, pyro, and fuel isspro ev2 electronic gauges on it. The fuel pressure was idling at 12PSI so we started investigating. We had replaced the overflow valve a few months ago with larry B unit and found out that it was bad by switching it out with a known good one. So we got a new one and still found that the pressure was idling around 16PSI and at WOT it dropped to 6PSI. So we got a new lift pump and put it on. We also deleted the fuel heater and installed a new OEM rubber hose 90* between the lift pump and fuel heater while we were there. We then got it up to 22PSI at idle but it would still drop off to about 6PSI at WOT. So we then went and dropped the tank and found the fuel lines were kinked where they went from steel lines to the plastic lines that connect to the tank. we got new OEM lines from dodge and cleaned out the tank and the sending unit while the tank was out so we know it clean and the line are good. The fuel pressure is still dropping off at WOT. So we then took the lines going to the filter head off and the filter head off and blew and cleaned them out. And the fuel pressure is still terrible. (all fuel pressure reading are coming off the outlet banjo bolt on the filter head. Its tapped and we have varrified them with 3 different mechanical gauges) He got fed up with it and we put a 100 plate in it and slid it to the middle of the pump and it will drop to 0PSI at WOT. It doesn't smoke at all when he floors it so it seems like its not getting fuel like the gauge says. But it still pulls hard till he shifts. The oil has no fuel in it and we have gone through the whole system and replaced almost everything to the injection pump. i dont know what to check next or where to look any help would be greatly appreciated.
PS sorry this is so long

Dieselbuilder

When its running try and pinch off the return line and see if the pressure comes up?

infidel

Probably just a typo but you should be measuring from the inlet banjo bolt.

Read> http://dodgeram.info/tsb/1996/14-07-96.htm

jstone44720

Do you mean the inlet to the fuel filter should be where the pressure is measured? Currently set up like figure 2 shows.

What is the expected difference in pressure between the inlet to the filter, and the inlet to the injection pump?

infidel

No, inlet to the injection pump.
You have it in the right place.
Cummins spec is no more than a 5 psi drop across the filter so until the filter starts plugging there should be no difference between the filter inlet and pump inlet.

Axtell3

I just went through some of your process myself, and while I didn't find kinked lines or much on the filters, pressure kept dropping, ( Though pinching the return line would peg my guage.
So I bought a tork tec overflow valve ( had allready replaced the original with a Larry version) Problem solved, for me. now I can pursue the fuel plates.