rickf

OK, Is the overflow on the suction side of the pump? If it is and it is where I think it is, right next to the fuel in line, then how can more fuel flow cool the pump module? That is what I hear EVERYONE say, more pressure gives more overflow to cool the pump. But if it is flowing out right where it is going in then it is not going to do anything to cool the module, It is nowhere near it. Second point/question, will fuel back flow through the pump? If so and if my previous idea is correct then a leak in the return line will cause the fuel to back flow all the way to the tank. What is in the pump will still be there but that is not enough to start on.

Rick
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KATOOM

Your questions are valid but here's why its not what you think it'd be.....
Just because the outlet is right next to the inlet doesn't mean that its simply an in/out process where by any excess fuel exits immediately. The fuel does actually enter the VP and winds around touching most internal parts. Matter of fact, by virtue of design, no fuel is supposed to pass through the VP when the engine is off and the VP shaft isn't turning. This was discovered when the idea of having a fuel pump continue to pump for a set amount of time after engine shut down for added cooling became impossible without some radical modifications to the VP. Now in saying that again, by virtue of design, it is possible when the engine is off to have the VP's internal ports which fuel passes through to align up some thereby allowing a little fuel to creep through. This is evident when bumping the starter will allow a minimal amount of fuel to dribble out the VP injector ports. But for all tense and purpose, no fuel is allowed to pass through while the engine is not running which means that also no air would be allowed to pass.

maxwellp

That also answers why the fuel pump does not run until the engine has started. Thanks

Dieseldude4x4

Mine has a hole somewhere on the suction side of the pump allowing the hose between the FASS and the tank to drain. I verified this when I pulled the FASS off. Both the line to the 44 and the recirc line were full of fuel but the suction line between the pump and the tank was empty. The pump use to build up pressure as soon as I would go to start the truck but now it takes several seconds to build pressure. And, the FASS noise level changes dramatically when it builds pressure finally. I have the big fuel suction line coming from KLM. I'm going to install it and close off the two stock lines. Parts should be here this week.

Dieseldude4x4

Well, finally got all the parts I need from three different auto parts stores locally and from FASS and KLM. Got the big 1/2 inch fuel suction kit that goes in the top of the tank. It looks like a real quality piece. Gotta drop the tank and drill a 1 1/2 inch hole to install the new adapter. It has both suction and return to the tank from the FASS. Got all new fuel line and a new wiring harness with the relay that gets a signal from the original lift pump wiring but gets power from the battery. Got the tank all disconnected and ready to drop. I figured I was going to do this so I ran it down to about ten gallons. I'm going to strap it to my motorcycle jack and lower it down to do the mods and then jack it back up in place. That is the plan in theory anyway. Going to plumb the on engine fuel filter and heater back into the system also to get the fuel heater back for winter time starting. Guess we'll see how that will work. I'm also adding a 0 - 15 psi gauge to the top of the fuel heater / filter assembly just as a back up to the electric gauge.

LeviMXUSMC

Wonderfull information KATOOM I will start looking for where I may have a small problum. It has just started if any one knows the most tipical place to start let me know.. Thanks.

krawler-N-tow

After changing my oil I'm pretty convinced there is fuel there. I'm also going to place bets on the crossover tubes & Orings needing to be replaced. Where can I get those? I've swapped injectors around 6 times and have never replaced those Orings.

This is all petty compared to my current issue. NV4500 won't go into any gear, left me stranded I have a Valair Clutch with the upgraded hydraulics with less than 25k on them. It was sometimes getting hard to get into 1st & reverse but this just came out of the blue.