I just finished replacing lift pump number four. I am replacing lift pumps every ~10,000 miles on average. Thankfully Cummins warranties thier parts for 12 months or 12,000 miles which I have yet to have one last more than. I get the exact same symptom every time, pressure will suddenly start droping down to 5psi or so and then go back to normal intermittently. I replace the pump and it's fine for another couple months then same thing all over again. The last time I installed a brand new pump and relocated it to the frame next to the tank with the Vulcan kit. This time the pump went out faster, this one lasted maybe 8,000 miles.

There HAS to be something causing the pumps to go on after the other so quickly. One thing I noticed when installing the Vulcan kit and again when I replaced this pump is that I get no fuel syphoning from the tank when the supply line is taken loose. Granted I wait until the tank is nearly empty but there is still 2-4 gallons left in the tank. Is it possible there is an air leak somewhere downstream from the pump allowing fuel to drain back into the tank leaving the pump to run dry everytime the truck is started? I can't think of anything else. Any ideas?

 

The stock pumps are junk. I was in the same boat until I bought FASS II. That ended the problem for me. I can't pull it lower that 15 PSI. They come with a 4 year, 400K mile warranty for $380.

There are a few guys here also experimenting with a Walbro pump set up that looks really promissing, but the jury is still out.

The quicker you dump the stock set up the better you will be. That is unless you like replacing LP's.

 

Seems odd...if there were air getting in...it seems there would be fuel coming out under pressure...I don't know

It does seem like you are burning through pumps though. I replaced my first one at 80,000 and then again at 95,000. I now am using the Carter P4601HP pump as a lift pump...I gave up on the stock replacement after I got one and it didn't work out of the box. When I moved my lift pump to the frame rail I made sure it was located below 1/2 on the tank. Now I also use Power Service religiously and try to keep the tank no less than 1/3 full to maintain a full pump. I was alarmed when I cut through the fuel line on the frame rail that no fuel came from the pump side of the line, only the tank side. I think what happens is that when the system is depressurized when you shut down your truck, the fuel in the lines balences out to the level; in the tank, so that there is actually air in the lines. This may still be the case now but relocated, at least the pump is never spinning free trying to suck fuel up the line.

I hope this made sense...

 

I should note that I keep to clamps, wrenches, and a spare pump in my truck at all times. So I guess some day I'll go with a FASS based upon what everyone here says.

 

I didn't like getting rid of the stock pump either. But with 4 failures, the decision was made for me. Get the most dependable and proven pump you can.

 

I've contemplated replacing the stock pump with something aftermarket but I have yet to find an alternative that I like. Just browsing online forums it seem FASS has a fair amount of failures and I've seen several threads indicating the customer service for FASS leaves something to be desired. I believe the mechanical belt-driven system still uses the lift pump so that one is automatically out. I also have no desire for complicated plumbing and piggy-back or bypass pumps. I guess I'm just hard to please.

The real kicker for me is that I am in the grading business and we run 30 or so pieces of equipment almost every day year round, all run on diesel. Everything from skid steers to 100,000 pound trackhoes to D8 dozers. They all run with very little down time and almost never any engine related issues. All the while I can't keep a light duty truck on the road with any real reliability. It's very frustrating.

 

Relocate the pump off the engine, back to the frame by the fuel tank, and you problems will go away. The solution is as simple as that.

 

If you read my first post you would see that I have done that and the pump died faster after doing just that.

 

wes there is one thing that comes to mind is your fuel filter my brother and i (before my fass) get ours from napa bro because he was in a hurry picked 1 up from advanced soon as he put it in the pressure droped way down to 4 psi at idol we pulled it out took it apart i dont see how fuel could go through the "cardboard" they use for medi in those crappy filters got another 1 from napa pressure went right back up (he's a lucky sob 170K on stock lp and vp44 still holded 10 psi dropen to about 7 at wot)

 

It is possible to have an air leak in the fuel module although not likely as it woud show symptoms more freequently.....a friends truck had a crack at the bottom of the mod and if he got below 1/4 tank all heck would break loose.

HAVE A LOOK AT THE PICK UP SCREEN! I too have gone through the dang thing is hard on lp's, well my truck ate the float for the sender and it plugged the pickup screen......not so good. If you have ever loaded the tank with dirty fuel it prolly picked up a bunch of crap on the screen......just a hunch.

 

Has any one ever thought of trying to put a fuel filter before the lift pump? I think I am going to in the next week or so. If you think about the internal workings of that pump it has to have a very small clearence between the housing and the rotors of the pump. If you get dirt through there and whats it going to do, it will score the pump and as it keeps doing this you get lower and lower performance. Thats just my opinion but I thought I would throw it out there and let you guys tear it up.

 

Which fuel conditioner do you use Wes?

 

Sorry, I didn't read your first post closely enough.

If you've moved the pump to the frame and the pump went out faster, then it could be there's a power problem which is made worse because of the longer wiring. What usually goes out on the stock lift pumps, which slowly loose pressure, is the internal bypass valve fails due to engine vibrations and fluid harmonics from the VP44. Instead, your pump motor may be failing due to a low voltage problem.

Another cause could be fuel contamination, as mentioned previously, which is wearing out the vane pump, itself. The fuel filter condition or an examination of the pump portion, itself, would give an indication of this problem. It's certainly easy enough to pull the cover off the pump and check the condition of the vanes. That's the only part of the pump which can be examined without destroying the whole thing.

One trick which was claimed to work many years back on the TDR was to take the top plate off the pump and flip it over. Many members claimed this improved pump pressure, but that fix always seemed doubtful to me.

Some have theorized that cavitation takes out the vane pump and internal pressure regulator, which prompted the whole pump relocation idea in the first place. The theory went..these pumps were never designed to suck. If this is the case with your truck, the fuel pickup in the tank could be plugged or could be sucking air. But if it's sucking air, then it would also probably be loosing prime and the engine would be hard to start after sitting for a while, which leaves a plugged pickup as a possible cause.

 

I've never had a problem slowly loosing pressure. The symptom is always the same, it suddenly starts dropping to ~5psi then will go back to normal intermittently. When this starts happening there are times the pump will run at normal pressures for 10-20 miles before the pressure drops again. The pressure drop is never gradual, it's always sudden and it fluctuates back and forth. This sounds like the regulator to me. I run no fuel conditioner, strait No. 2.

Is the only way to check the pickup to drop the tank?

 

This one's a long shot but:

Open your filter can and drain it.... Then look for "bio-slime". The bio slime could be clogging up your water separator. If that's the case, powerservice has a product that can clear this up.

Also, did you try the campaign/recall pump? I'd really look for the underlying problem, but if the replacement pumps are that bad maybe the campaign pump would be something to try..?

Best of luck