Hello all,

I did an extensive mod so I could run waste oil on a 96 Dodge 250 5.9 with about 240,000 mi on it a few years ago, but have been running diesel due to current low cost. In all my searches online I see a lot of people with lift pump pressure problems due to the overflow valve but no comments about my problem.

I have a pressure gauge on the line just before the injection pump. When I completed my mods (see below), I was still getting about 30psi with mild needle wiggle that was in sync with each engine revolution/lift pump pulse. I ran maybe 1/2 tank of 90/10 ratio WMO/diesel just to test to make sure the mod worked well, and actually got better power and fuel economy with the WMO but stayed with diesel due to fuel prices being down and until I can find someone willing to part with their WMO other than what little I produce on my own.

Over time the needle wiggle got to be more of a bounce, then worse to where needle would bounce from 0 to 30 with each pulse, then to where it would really bang the needle on 0 and barely lift up to maybe 5psi on the bounce. Concerns of not wanting to damage the injection pump but not knowing for sure where the problem lie, I replaced both inline filters (an add-on that is just after the tank as well as the stock filter) and also the lift pump. I got better pressure and the needle bounce goes from about 5psi to up to about 40psi but the needle bounce is still very strong. The degradation and the needle bounce issue occurred over probably 3-5000 mi.

Has my overflow valve worn out/gone bad to where it's bleeding off most all the pressure the lift pump produces creating the excessive needle bounce?

Following is mods I've done and a few stats. Oil pressure at idle is 30psi and about 60psi @ 1,700rpm. The kid that had it before put on an adjustable pot to control the overdrive engagement and someone told me that the strong engine shudder that occurs with gentle acceleration from stop may be due to him messing with the throttle plate as a means to increase HP (not sure).

I took out the stock fuel heater due to it's inherent leaking problem. Fuel flow from tank goes first into a custom electric thermostat controlled heater block that kicks out once the water temp gets hot. Then it goes into a combination hot water heater/filter unit that filters down to probably 7-8 microns and heats the fuel all the time. Then it goes into the lift pump and then into the stock filter. From there it goes into a second electric thermostat controlled heater block that is just before the injector that kicks in only if fuel / engine is cold. Keep in mind that initially after my mods, I was getting a solid 30psi right at the injector pump with the old lift pump with just a little needle wiggle that was in sync with the engine/lift pump cycle. I would think that if the mods or extra filter was creating too much drag, I would not have seen the initial 30psi or now see the 40+psi peaks on the extreme needle bounce after replacing filters and lift pump, but a lower max pressure, and I haven't put that much milage or fuel through the truck since the mod's, and what WMO I did use is filtered down to 1 micron, so there hasn't been much trash put through the filters to load them down. I'm thinking the new Lift pump is what brought the max pressure back up, but for the life of me, can't figure out what causes the huge pressure bounce with each lift pump cycle unless the overflow valve is bad and is bleeding off a huge amount of fuel that the lift pump is trying to provide to where the pressure immediately bleeds off after each initial lift pump pulse?

If anyone has experienced this and found out what causes this and how to fix, any feedback would be appreciated. I don't want to have to replace a damaged injector pump...

Thanks!

 

Howdy again,

Posted this a couple days ago. If anyone has any feeedback, would be appreciated. My regular commuter vehicle is down with a different problem and don't have time to fix and am dependent on using this truck as a daily driver for now and am worried about possibly causing damage to the injector pump, so am needing to find out what might be going on so I can fix it.

Thanks!