Engine/Transmission (1998.5 - 2002) LP thoughts...(long)

[d.miner]

Thanks Gary !

 

[ceastmen]

Gary-KJ6Q,

Is there any way to test the stock lift pump with a multimeter?

I too have read about all of the lift pump failures. When

mine quit I eliminated it for fear of being in the middle of

nowhere again!

I still have the stock lift pump and all hoses in a box.

So before I pitch it I would like to know, if it could be used as a

back up if my back up fails (redundant I know). Where I had a

failure was a very bad place to have a lift pump failure, thats

another story.

Thanks Chuck

 

[Gary - K7GLD]

Other than a pure open winding or failed brushes, not much to effectively measure with an ohmmeter - should be nearly a direct short across the power terminals, and NO continuity from either power post to the outer case.



Best way to check the pump if you have or can get a guage, is to actually connect power to the pump with hoses connected and pumping fuel from a source with the guage in line to monitor PSI - you can restrict or kink the lines to determine whether or not the pump will reach and maintain rated PSI. In my case, I simply placed a supply hose into my aux fuel tank, placed a T conector on the output to a guage, and returned the fuel flow back into the tank - I had a spare 12 volt battery to use for operating the pump during my test - and found my "bad" LP was just fine - it's now my spare...

 

[rweis]

Gary,



My purpose of the regulator is to bypass anything over 12psi. The LP runs easier and applying that to your wireing theory it takes less amperage because it is not working as hard because it only has to do a max of 12psi.



I did it to keep the check valve closed to eliminate that failure point. But a side benefit is it spins easier with less head pressure.



Maybe I'll put an amp gauge on it and watch it for a while. Someone else put an amp gauge on their stock one and we'll compare the currant draws.



My take at least. I'll know in another 220,000 miles (30,000 so far).

 

[jjohn]

rweis, where is the Reg located and where is the overflow returned to the tank?

Between the filter housing and vp44?



What brand regulator?



Thanks JJ

 

[Gary - K7GLD]

The regulators are a nice addition - keeps PSI nice and even - but I figured mine was OK enough, especially when the regulators run somewhere over $100...



If you do an amp draw test. post the results - I can't find the thread that had that info from some time back... I *did notice the LP motor lugs down noticeably as you restrict the pressure/flow up to max - it's bound to suck lots more current in the process...

 

[rweis]

JJ,



I used a Mallory 4307m and put it on the frame right after the lp. I have my lp down on the frame by the tank. I did the return back to the tank "burp" line.



I used the Mallory because it had large input and output ports so it would not restrict any flow.



I got it at a local true auto parts store (not one of the chain stores). It was about $120 as I remember.



Bob Weis

 

[15w40]

I also had questions about the wiring to the lift pump and being curious, I did some digging. What I found out about the lift pump wiring and connectors follows:



Deutsch makes the lift pump connector. It is the DT series P012. It is designed to carry 13 amps continuously and is used with 18 AWG wire in our application. The maximum current that the lift pump can draw is dependant on the pressure it is making and is a maximum of 4. 8 amps with the pump dead headed, or blocked off. The 18 AWG wire will allow 12 amps of current to flow without a problem. The connectors consists of a female end which connects to the ECM, part no. DT04-2S and a male end that is attached to the lift pump, part no. DT04-2P. These connectors withstand immersion in 3 feet of water without loss of electrical qualities or leakage. They show no evidence of corrosion after exposure to 48 hours of salt spray per MIL-STD 1344 method 1001.



I guess those having problems with the lift pump connections must have experienced 49 hours of salt spray.





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[Gary - K7GLD]

Thanks for the info and pics Dave - the one fairly typical characteristic of this type connector, has been that they frequently easily deform, open up, and lose firm contact with their mating surface - a second weakness is the crimped connection to the connector itself (see pic above), which can deteriorate over time and degrade current flow regardless of how good the actual connector itself is...



For reference, I have had to completely remove all crimped-on connections on my 5th wheel (an '88 model), even though externally they SEEMED tight and solid - multimeter tests showed as much as 3 volts loss thru some of them under nominal load - and physically opening them revealed substantial corrosion not externally evident. As many as possible, those in my main wiring harness between truck and trailer are now soldered solid, NO connectors, all others that had to remain with various lugs, were both crimped AND soldered, completely eliminating voltage/current losses thru them - and some of those, primarily down at the brake drums, were aslo extremely weather proofed...

 

[15w40]

Gary, I agree that this style connector can and will fail if subjected to vibration. How long will it last? Who knows? One idea I had about the problem is if those with bad connectors have properly installed the wiring harness. On my ‘98 the connector from the lift pump is clamped at the top of the pump. The wire from the ECM clips into the mating connector to form a rigid connection. If I was lazy and did not clamp the connector to the lift pump, it would be in constant vibration and may fail. I do not know if all model years clamped the connector, but if they do, and yours isn’t, there may be a problem.



I tried to get a picture of the metallic clamp on top of the pump but it is buried under the fuel filter with no good angle for a shot.

 

[Rescue]

Connections

Gary KJ6Q,



How about the guys that have the FP gauge check and log their pressures before and then after cleaning the LP connectors.



It might show a pattern, if LP pressures go up after cleaning the pins and applying a little dielectric grease.

 

[Gary - K7GLD]

Any info is likely to help particularly interested in hearing from any who DO find dirty contacts were the problem, rather than a bad pump - I have NO illusions this is a main cause, but at least one of several possible ones - and certainly easy to check for...