Engine/Transmission (1998.5 - 2002) Pressure regulator question

[mbelanger76]

I am currently troubleshooting a fuel pressure loss issue. Outlined in a thread I started FASS RELOCATION KIT. I noticed the line from the fuel pressure regulator which comes off the VP44 Tees off behind the engine block on its way back to the tank. Can any one tell me what that line is for and or where it comes from?

 

[Bob4x4]

That is the injector return line from the injectors (rifle drilled passage through head)

 

[mbelanger76]

Is there any way I can lose that much pressure through that line?

 

[Bob4x4]

Virtually no pressure in the return side. Are you sure your pump is not dying????

 

[mdilling]

That fitting is a pressure regulator with a metered bleed back to tank. If the spring behind the ball breaks it could cause a pressure drop. In larger Cummins engines they will die when returned to idle and then won't start.

 

[mbelanger76]

First thing I did was replace the lift pump. When I start the truck psi goes to 15 and drops off to zero within 5 min or so then truck dies

 

[mbelanger76]

So last night I disconnected the fuel line from the fuel tank module and dropped it in a fuel can. Ran the truck and it did the same thing, pressure dropped off to 0 after a couple minutes. When I got out of the truck fuel was gushing out of the Fuel tank module and the tank was pressured up. I had previously pulled the pressure regulator off the VP and it bench tested ok plus it was replaced after that. Can that much fuel be coming out of the pressure regulator/injector return line?

 

[BarryG]

If I recall the vp sends 70-80% of the fuel back to the tank as it is used for cooling the vp (perhaps more at idle). With the fuel being pulled from the fuel can instead of out of the fuel module there is nothing in the module to draw fuel out hence the overflow. Which might also make sense for the pressurization, there is nothing sucking out the fuel to reduce the pressure just pressure going in nothing coming out (minimal as it may be from the return line but it could add up as time goes by). That may make no sense and may be completely wrong but it works in my feeble head. That is not to say there is not an issue as there obviously is but you have tested and confirmed that it is not the fuel module or pickup causing the issue since it did it without drawing fuel through the module.

 

[mbelanger76]

Didn't know that much fuel was returned to the tank. It does make sense when you think about it.

 

[mbelanger76]

Bob, can you explain the flow from the injectors to the return line? Is this excess pressure from the injectors or injector leak by?

 

[Bob4x4]

All diesels have a provision for injector return flow-it is a very small amount unless there is a problem such as a connector tube or o-ring that is leaking.

Approximately 70 % of the fuel fed to the vp44 is returned to the tank.

You may want to separate your returns to see how much is returning from your injectors vs the vp. I have not seen any specs for the vp injectors,but it should be small.

 

[Bob4x4]

So last night I disconnected the fuel line from the fuel tank module and dropped it in a fuel can. Ran the truck and it did the same thing, pressure dropped off to 0 after a couple minutes. When I got out of the truck fuel was gushing out of the Fuel tank module and the tank was pressured up. I had previously pulled the pressure regulator off the VP and it bench tested ok plus it was replaced after that. Can that much fuel be coming out of the pressure regulator/injector return line?

That test still leaves the fuel line in the ckt. I have seen lines fail with out leaking but will suck air... ... ... ...

 

[mbelanger76]

I ran a new fuel line/hose from the tank to the LP and had the same results. So the 70% is from the VP pressure regulator not the port in the back of the head correct?

 

[mbelanger76]

Here is a list of things I tried thus far.
This problem started a month ago while driving my truck started to stumble, looked at my fuel pressure gauge and it was at 0, was able to get home and thought the lift pump failed so I replaced it and truck had good pressure but dropped off to 0 while running truck that's when I called a mechanic. He thought the pump was shutting off for some reason so wired it up to the ignition switch, still doing the same thing. Replace pressure regulator, same problem. Dropped tank installed jeep module, no luck. Replaced fuel line from tank to pump, removed lines from lift pump to VP44 and cleaned out, same problem. Pulled fuel filter housing and found metal pieces I the heating element cleaned that all out reinstalled and same problem. by passed fuel filter, ran line to LP from a fuel can,when I turn the ignition on the pressure reaches 15 psi and stays there, Once it is running pressure drops to about 9 and each time I rev the engine the pressure drops and drops and drops till we're at 0, At that point engine starves and stops

 

[mbelanger76]

Finally solved the problem, I retraced my steps and after the fuel module replacement debris from the tank must have migrated into the banjo bolt screen which I had cleaned out initially. Truck is back on the road thanks for all the help.

 

[tdwalton]

On a trip from Washington to California my lift pump pressure gauge started dropping from 12 to 6 whenever I had to back off on the speed. It was a long trip and all was well so long as I kept pressure on the fuel pedal. When I had to slow, the pressure gauge would drop to 6 and I had to rev the engine to get it back up to 12 again. As soon as I was able to speed up it stayed steady at 12. I ran it like that for a couple hundred miles. I reached my destination and the truck set for a day. The next time I got in it the same thing happened. I drove for about 120 miles and when I stopped this time, the pressure gauge stayed steady at 12 and has ever since. No more problems. What could possibly cause the lift pump pressure gauge to drop and then run fine?

 

[Bob4x4]

batt voltage

 

[tdwalton]

nope, don't think so, but thanks