Archived no/low fuel pressure :(

[DAlford]

**Mods: if this doesn't technically qualify as a 'disabled truck’ please move this thread. I'm not sure if the problem I'm having is fuel related or mechanical/electrical related, and for fear of damaging my VP44, the truck is voluntarily out of commission (parked in the back of the parking lot) at the office and I'm driving another vehicle. Because of the location (unlit parking lot), I’d like to address the problem asap so that I can at least drive it ~20 back to the house and work on it there.



wow, where to begin...



Long story short: When I bump the engine and allow the Raptor to run for ~30 seconds, the pressure is up around the 13-14psi area. When I start the engine, the pressure immediately drops to 10, then gradually to ~5 while idling. As soon as there is a load applied (first gear to move the truck), it drops sub 5 and, within ~10 seconds is almost to 0..... at which point I kill the engine and let it sit (again, for fear of the VP44).



Background:



I've got a ~B50 blend (commercially bought B100 blended with pump diesel) in the truck right now and have noticed the pressure dropping slowly over the past couple days. The temperature has dropped as low as the 40s but has been in the 50s most of the time I’ve tinkered with it. I don’t think (... I know, I know: famous last words I’m having a gelling issue as I can open the fuel/water separator and perfectly clear and liquid fuel drains out even after the truck has sat there overnight (without either block heat or fuel heater in the picture)



Thinking that I might have a plugged fuel filter, I changed it and the problem did not go away (the old filter had ~8k and it was not the first I’d changed after starting running Bio).



There are no codes in the computer (P or E).



The truck idles fine... I just don’t want to damage the VP44.



Any ideas?

 

[JLandry]

Are you sure the Raptor pump is working properly?



Another idea... are you still using the original fuel pickup inside the tank? If so, could it be the fuel inlet screen on the bottom of the fuel module is clogging up from contamination in the fuel?



Maybe it might be worth siphoning or pumping some fuel out through the tank filler neck just to see what it looks like. If it looks bad, then you'll know you probably need to drain and drop the tank and clean the fuel pickup screen.



Please keep us posted.



Good luck,



John L.

 

[MAleshire]

Biodiesel has extremely high solvent properties. It can and will dissolve standard diesel rated fuel hose. A 50% blend will eventually create stock fuel line problems. Also, any crude or rust in the fuel tank and along the way to the fuel filter will be loosened up by that high a concentration of biodiesel. Anything that could plug up from the loosened up crude could be a problem. The specific problem you are having right now could be caused by a bad fuel line on the supply side sucking air. The lift pump can't pump air, so when there is a demand increase the fuel pressure drops. It could also be a bad lift pump. Too bad you can't tell what's going on with fuel pressure at highway speed----that would give more info. I think I'd start with the line between the tank and the lift pump, then check the pump itself. If all that checks out OK then look at the return valve and then the tank. Good luck with the problem.

Skip

 

[Sticks]

Is your fuel pressure sensor pre or post filter? - READ Where in your system is the sensor located?

 

[DAlford]

thanks for the help with this one and sorry for the long lag time in replying.



Regarding the questions asked / possible issue: I replaced the fuel line from the tank all the way to the VP44 with bio-approved fuel hose (little chance that there could be an issue there). The fuel pressure is measured post-filter right at the VP44 (banjo bolt take-off for a 1/4in hose for the electronic pressure sensor... if that's the proper names for everything)



Turns out that the bio I had in the truck was more of a 'summer blend' with a ~55-60F cloud point and a gell-point that was not much lower than that. I thought the 50/50 mixture ratio would be enough to keep the bio from doing its gelling deal but apparently not.



After pulling a little more than 30 gallons out of the tank (into barrels), topping off with regular pump diesel and replacing yet another fuel filter (the one in there had a waxy/pasty coating of gelled crap on it; this later 'melted' off the filter once warmed up with paper towels wrapped around it), things are back to normal. In addition to changing the filter, I held a hair dryer to the Raptor to warm it up a bit; if the innards are anything like the stock Carter pump, which has a screen around the 'impeller' of the pump, I thought the gelled Bio could have clogged/bogged the pump from delivering it full potential volume... . just as it plugged the filter up with that layer of slim.



My personal take-away from all this: no more than 5-15% bio in the winter; gonna save the strong blends for the summer time



Thanks for all the help yall!