Ok guys could use some input. My truck is y2k 24v auto with a fass 95 lift pump and an reman vp44. If I parked it up hill it has to be reprimed in the morning . (Starter bump type) I put in a check valve on the discharge side of the lift pump by the tank which solved the priming/drain back issue, but I don't know why the fuel was draining back. I have no leaks and no

smell and run 14-16 psi on the fp gauge. When the truck is at lower rpms under load light or heavy I can feel a little bit of surging like a miss. All of the return lines seals have been replaced already . If there's is a leak how can I find it and could it be in the injector pump check valve. Thanks for the help

Edited September 15, 20159 yr by jigdog

Maybe I missed something. If you installed a check valve and that solved your priming issue, What makes you think the fuel is draining back?

Ok guys could use some input. My truck is y2k 24v auto with a fass 95 lift pump and an reman vp44. If I parked it up hill it has to be reprimed in the morning . (Starter bump type) I put in a check valve on the discharge side of the lift pump by the tank which solved the priming/drain back issue, but I don't know why the fuel was draining back. I have no leaks and no

smell and run 14-16 psi on the fp gauge. When the truck is at lower rpms under load light or heavy I can feel a little bit of surging like a miss. All of the return lines seals have been replaced already . If there's is a leak how can I find it and could it be in the injector pump check valve. Thanks for the help

Who is the rebuilder for the VP44 you purchased? If your loosing prime I would look at your fuel lines. Including the fuel return at the back of the head. This particular line uses two 12mm banjo sealing washers and over the years can dry rot.

The surging miss could be a loose connector tube or injector line but chances are it may be your VP44. I have a similar issue on my truck due to the VP44 being programmed for an HO truck.

Edited September 15, 20159 yr by Vais01

All of the return lines seals have been replaced already. I got the vp44 from Vulcan performance I think he said it came from Illinois .

If it is not in the fuel line between the tank and the injector pump or back to the return side to the tank and no leaks I can see ,could I be losing it inside the inj pump.

I know the check valve will solve a lot of problems for priming but that is just showing you sill have a problem. Some how air is being pulled into the fuel system and allowing the fuel to drain back. I would look at the suction side of the fuel system a bit closer. Typically they never leak outwards because its under a suction/vacuum while running and when the engine is off its still gain a vacuum and pulls air in. The air naturally rises in the fuel system and drains it back to the tank.

I know the check valve will solve a lot of problems for priming but that is just showing you sill have a problem. Some how air is being pulled into the fuel system and allowing the fuel to drain back. I would look at the suction side of the fuel system a bit closer. Typically they never leak outwards because its under a suction/vacuum while running and when the engine is off its still gain a vacuum and pulls air in. The air naturally rises in the fuel system and drains it back to the tank.

Agreed perhaps a loose fitting that is allowing air to be drawn in after shutdown but not fuel to leak out. I'd say if you have a QD type fitting I'd check the seals.

Thanks for the info both of you. So I should be looking for air getting in the system between the lift pump and the inj pump or between the tank pickup and the lift pump .

Thanks for the info both of you. So I should be looking for air getting in the system between the lift pump and the inj pump or between the tank pickup and the lift pump .

 

Between the tank and lift pump. Yes...

 

Any line that have pressure will naturally leaks outwards. So between the lift pump and Injection pump would be pressurized so that would leak outwards. Now the line between the fuel tank and the lift pump is all suction line and would not show a outward leak because of the nature of the line its got a vacuum while running and a vacuum while losing prime.

Between the tank and lift pump. Yes...

 

Any line that have pressure will naturally leaks outwards. So between the lift pump and Injection pump would be pressurized so that would leak outwards. Now the line between the fuel tank and the lift pump is all suction line and would not show a outward leak because of the nature of the line its got a vacuum while running and a vacuum while losing prime.

I agree. Chances are on of the quick connect fittings has a bad seal in it or the threaded fittings on the pump are loose. 

I was loosing prime with tank drain back once. I was too chicken to tighten the factory fuel filter cap, thought It would break or crack being made of plastic.

I read to torque the cap down to 25 ft. pounds and my problem went away. I've also read you can have an injector tight enough to not leak fuel but still allow air to get drain back and loss of prime.

Ok still have uphill parking prime loss. Had it in the shop they had tank off and checked the line from the lift pump to inj pump and pressurized the line from the inj pump to the tank with no leaks.they put a clear line in between the filter and the inj pump and found no air. If you face it down hill overnight it starts right up but has to be reprised when pointed up hill. Here's the real puzzle

,if they park it nose up at their shop it starts up,if I drive it home and park it nose up it has to be reprimed. They have given up on it to tell me they can't fix it I have to just drive it until whatever is wrong breaks. They think it could be the vp from advice from the vp suppliers and others.i got no results and none of my $550 back. I think they are not parking it after a road run as I am. The truck also has a slight ruff idle intermittent more prevalent when the weather is warm.the vp is five year old without a new brain. What do you guys think.

Alright jigdog, I just got done chasing down every thread possible on this exact issue as I was having the same issues. I'll list out everything I've found that could be the potential, and then what I THINK fixed mine.

 

From my findings, anytime you park uphill and loose prime and park downhill but maintain prime points to a leak in the RETURN side of the fuel system. Possible causes to this could be the following;

 

-Banjo bolt washers at the back of the head

-Grommets at the return TEE from the banjo and the VP

-Overflow valve at the VP

-Crossover tube o-rings

-Any return fitting associated with your FASS being loose

 

I started on mine with new washers on the banjo bolt at the back of the head and tightened down the fittings at the TEE directly down from the banjo bolt on the back of the head. No joy

 

Tried tracking down the grommets that fit in the TEE, found some at Geno's but they're back ordered. In the meantime I decided to check my return line fitting for my FASS and I got an extra 1/8th-1/4 turn out of it and it seems to have fixed my issue. With this I was also have erratic fuel pressure gauge readings. I tightened that return line fitting about 100-150 miles ago and TODAY it seems as if all the air that was in my system causing this issue have worked itself out. I no longer have erratic fuel pressures and I'm 1 for 1 on quick start ups after being parked nose up over night.

 

Hope this helps!

Thanks notlimah for the help I think we have ruled out the return side do to seal replacement and if you crimp off any spot on the suction side of the vp44 it starts right up, all the way to the tank.?

Ok so all seals at the fuel return TEE have been replaced? THIS  part from Geno's? 

 

Return lines at the FASS are as tight as they can get? FASS filters are tight?

 

Sorry if this seems redundant but your symptoms scream leak on the return side. Only other thing I think it could be would be injector O-rings.

 

Unless you have an original VP44, I don't see anything on the inner 'diaphragm' being the issue as they fixed that.

The shop did the tube seals first and I had the return stuff all done last year and the truck starts if you block the drain back at any point on the intake side,vp to the tank so the drain back has to be on the intake side. they put time in on it and all they work on mostly is cummins pickups,they were stumped.

 

The way I read this, is it all started after the Fass 95 was installed?

 

I had a problems with my Fass 150 when my truck got to half a tank and I turned the truck off at gas station (or wherever) it would loose prime. I would half to put 6-12 gallons back in truck and crack injector line to get it running again. 

 

After a couple of trips to mechanics shop they finally figured out my water separator drain was letting air in the system and making it loose prime. (Or so I was told)

Thanks 903 I had the water sep valve replaced with oem recently I am thinking about my oem lp that's still li place and trying to plumb it in to rule out the fass which runs #16 at idle. Should the fass be able hold all the fuel above the pump with out a drain back , if there's a open line letting air in?

If there's a leak there's a leak. The FASS won't hold the fuel in the lines. Once all the air is out of the fuel system, it will stay under pressure. If you're loosing prime then there's a leak somewhere. Especially on the return side, you won't see a physical leak, that's why going back through and snugging up any and everything can solve your problem. It fixed mine and I had already done a lot of what you did and turns out it was a simple JIC fitting that was a little loose.

The shop that worked on it pressurized it from the vp back and soap sparyed it with no sign of leaks. Their vp rebuilder thinks it's 

the vp and it has a leak inside in the pump part of the vp.

I have a hard time believing the leak is coming from the VP44, especially since you got it from Vulcan. I've never heard of a prime issue being because of a VP, especially a new/rebuilt pump.

 

 

In that pic, have you replaced the washers for #4 & #5 in both locations?

Have the grommets that attach to the #3 been replaced?

Have the crossover tube o-rings been replaced?

Have you made sure the return line on the FASS is tight or any washers or o-rings are in good condition?

 

It would just suck to shell out money for a new VP and it doesn't fix the issue ya know?