Engine/Transmission (1998.5 - 2002) The REAL Lift Pump Test!

[Leo Bennett]

I finally got a FP gauge for my 01 ETH, and (momentarlily) put it on the intake side of the filter, got 8-9 psi at idle. My service manual says it should be at least 10 psi. So took it to my friendly Dodge dealer, who presented me with a bill for $40 for testing it and said it was fine.



I argued, he said psi is no longer a criteria for lift pump diagnosis, and presented me with a copy of TSB 14-002-03, dated April 11, 2003. (Which I don't see in the recent TSB summary. )



It defines an "improved diagnostic procedure" for lift pumps involving, among other things, measuring the flow produced in front of the VP44 with the 25 second starter bump run. 45 fluid ounces or more is goodness. PSI is irrelevent, unless the fluid test fails. I had 48, so he patted me on the head and said pay your bill an go home.



Anyone else encountered this? Is the FP gauge still useful?

 

[Hohn]

Fp is totally useful. Getting that gauge is still good advice.



The relationship between pressure and volume has been hashed out here repeatedly. Pressure can be an indicator of flow or of restriction-- depending on where it is. Keeping an eye on psi will help you to know that the flow is there.



Justin

 

[Sticks]

IMO the engineers are trying to cut down on the number of replacements with this new testing theory. Unless you are seeing fluctuating pressures, or can pull it below 5 while highway cruising, you may as well go to Cummins or other big rig shops and buy a new LP and take care of it yourself.



And while you are thinking about that... You might want to either relocate it to the frame rail with upgraded lines (larger) or install an aftermarket kit. The downside to that is goodbye VP44 warranty.

 

[CFAR]

But they can't test the volume at wot can they?

 

[Scott Elliott]

Leo, that is exactly what happened to me. I have a 2002 2500 ETC. In January, I took mine to Carlin Dodge on Woodmen. I had 0 psi at WOT. Changing the fuel filter did not make any difference. I had tried cleaning the lift pump wire connections with no luck. I had approximately 32000 miles on it at the time. They told me the same thing, they don't go by psi but volume. They said my pump was at 50 oz, so it was ok. I was surprised. On the plus side, they found an inoperative air intake heater relay and they replaced that under warranty.



Fine, I will wait for the dead lift pump to kill the vp and I will let them replace it. I have 65000 miles to go.



My fp guage died a few weeks ago and I am waiting for the replacement, so I have no idea what my numbers are now.



Scott

 

[A Johnson]

Yup, fuel volume is just great when you have it. How are you going to monitor volume going down the road? You aren't, so a gauge to measure that is still the best for detecting intermittant problems. I think we all know the lift pumps will start giving intermittant pressures as an indication of an impending failure. Also may indicate bad conections as some have found.



A Johnson

 

[mhenon]

LP problems!

I wonder how many lift pump problems are actually a plugged screen on the supply line with-in the tank. After reading all the threads about this, especially those guys with multiple LP failures, it makes you start to consider something other than the pump itself.

We've already heard about poor electrical connections causing the pump to act up. How about the person getting a really crappy load of fuel... . the screen in the tank gets partially plugged... . and from that day on his pump (pumps) are working under an extreme load. No matter how many LP's go on that rig their going to fail somewhere down the line.

I still want to get in the tank and remove that damn screen. Just can't see having a filter (of any kind) that can't be serviced or looked at. It's just a pain in the a** to get to it.

Somebody here talked about pulling his bed to get the screen out and I just might do that this year. Toss the 3/8 line and screen and install a 1/2 line. I think Jannetty has a 1/2" kit.



Mike

 

[JStephens]

According to my gauge my pressure fluctuates btw 14 to 16 at an idle. Just a bit of a flutter in the needle and may just 1 psi or so difference. Does this flutter mean my LP is headed south? and if so would my wildcat maxflow system void any warranty on LP VP? Just need some advice before I start to worrry.

 

[Ncostello]

mhenon... take a look at whats inside the fuel module here...



99 fuel module insides



I too was not happy having a screen in the tank. So I carefully cut it out with an exacto knife. Just be sure to put a prefilter inline somewhere between the lift pump and the tank.



The problem I see with the volume test is this... when you disconnect the fitting at the VP, you basically remove alot of restriction. Thus the lift pump can no longer build pressures anywhere near 15psi. The lift pump has an internall spill over or bypass valve to recirculate fuel internally if 15psi or so is acheived. If that bypass valve spring weakens then it would rather bypass fuel internally than push it through a restriction such as the VP44. SO when you remove the VP fitting it will gladly flow plenty of fuel into a container under relatively low pressure. As soon as you hook the fuel line back up you now have a high restriction which causes the bypass valve to operate open again. Fuel will recirc inside the pump now versus flow to the VP. You then are able to pull more fuel out of the line than can be delivered and you'll have low gauge pressure readings.



A good lift pump will idle at 15psi. WOT might result in pressures as low as 10 or 8 psi. On a bad one the bypass valve is opening at say 10psi... it would stand to reason you could pull it down to 3-4 psi or lower depending. But with no restriction... the bypass never has to operate at all and you'll see volume OK.

 

[monkfarm]

A friend of mine had a maple leaf floating around in his fuel tank in a ww2 jeep 289 powered. He did everything before he discovered it. Just every once in a while that ol' maple leaf would float up to the intake and foul everything up.