Engine/Transmission (1998.5 - 2002) lift pump

[Don Bellamy]

Could anyone tell me where the 12v comes from that powers the lift pump? When truck don't start I can check voltage coming to the pump and there won't be any, I can turn the key to the off position and again try to start and it will?

Don

 

[BDaugherty]

Could you rephrase your question? The power for the lift pump comes from the ECM and then through a relay on its way to the pump.

 

[blacksheepdiesel]

Don,

The lift pump comes on momentarily (like 1/2 a second) when the key is switched on. When the starter is bumped the pump runs for several seconds. When the engine starts it runs continuously.

Like BDaugherty, the ECM triggers a relay to control the lift pump.

Godspeed,
Trent

 

[JLandry]

Guys,



There is no relay in the lift pump circuit. The lift pump is powered directly from the ECM with no fuse or relay in between.



Don't let that relay labeled "FUEL PUMP" in the PDC (Power DIstribution Center) fool you... that's for the VP44 fuel injection pump.



If the 12 volts isn't present for about 25 seconds on the lift pump wiring harness when you bump the starter, then there's either a problem with the wiring harness, the ECM connector, or the ECM itself.



Use a voltmeter to check the harness and let us know what you find out.



Good luck,



John L.

 

[Gary - K7GLD]

Guys,



There is no relay in the lift pump circuit. The lift is powered directly from the ECM with no fuse or relay in between.



If the 12 volts isn't present for about 25 seconds on the lift pump wiring harness when you bump the starter, then there's either a problem with the wiring harness, the ECM connector, or the ECM itself.



Use a voltmeter to check the harness and let us know what you find out.



Good luck,



John L.

YUP - what John said!



NO relay built into the LP circuit, all control comes direct from the ECM - and some of us who have modded the LP part of the fuel system often DO add a control relay, to remove any unusual loads from the expensive ECM...

 

[Joe Mc]

Couldn't you connect the pump 12v+ to a key on only circuit, fuse the wire and not worry about the ECM??? I guess the stock LP could get damaged running without moving fluid, like when it's cold and wait to start stays on for a while?

 

[Gary - K7GLD]

Couldn't you connect the pump 12v+ to a key on only circuit, fuse the wire and not worry about the ECM??? I guess the stock LP could get damaged running without moving fluid, like when it's cold and wait to start stays on for a while?

VP-44 equipped trucks will not start if the pump detects above about 7 PSI at startup - so the LP only runs long enough to prime the system, then shuts down until the engine starts and is running - so altering the system so the LP operates whenever the ignition is on won't work, and is probably unsafe in case of collision as well...

 

[Don Bellamy]

Thanks for the info, another clue is that I can be driving and all at once there will be no fuel pressure, I can turn the key off then restart and all is well. It may not happen for a month then it may happen several time in a week?

Don

 

[JLandry]

Thanks for the info, another clue is that I can be driving and all at once there will be no fuel pressure, I can turn the key off then restart and all is well. It may not happen for a month then it may happen several time in a week?

Don

Don,



Is this is a stock lift pump? If so, I'd be tempted to suspect it as the culprit.



If you can't nail down whether the pump is actually loosing power (from the ECM) when this condition occurs, then you might want to go ahead and replace the lift pump with an aftermarket version just for good measure. I'm sort of partial to the Airtex gearotor type pump at only $149. 99 delivered from Diesel Distributors. It can be installed in the stock location or on the frame with a relocation kit.



You might also consider running wires from the lift pump wiring harness into the truck cab so you can monitor the voltage real time with a voltmeter to see what's happening when you loose pressure.



Good luck,



John L.

 

[nuv22]

guys i am having the same problem as Don. i too was wondering where the voltage for the pump came from. so i just changed my pump to the new airtex pump and SAME thing happens. i will turn it on and driver and have 15-16 psi then stop at the store and get back in to go home and wham only 6 psi? so i waited until it happened again and jumped under the truck and took a voltage reading and the pump was only getting 5-6 volts. what gives? is it the ecm? if so what could i connect the pump to so that its only on when the engine is running? any help would be great guys im pulling my hair out on this one!

 

[Hobart]

I may have the same problem. Started loosing pressure (bouncing from 8 to 0 lbs)and i expect an electrical problem. Cleaned the contact at the battery (I've got the intanker) and seems to be ok for now. Are you getting a code? I get 237 which seems to imply lost power to the pump according to some. Next I will unhook from the relay and clean and grease.

 

[JLandry]

guys i am having the same problem as Don.

Have you tried disconnecting the connector at the ECM and cleaning the contacts with some contact cleaner?



Also, remove, clean, and reattach any ground connections you can find in the engine compartment.



If it isn't a problem with the grounds or wiring harness, then it must be an internal problem with the ECM. I assume the ECM has an electronic relay internally for the lift pump, so it's possible this is acting up.



Good luck,



John L.

 

[nuv22]

Yes I checked the connectors when I put the new pump in and also put dielectric grease on the connectors. All my grounds are fine I went trough them when I had the TC lock unlock. If I wanted to bypass the ECM for right now do you know what I could hook it up to that has 12v ONLY when the engine is running? I have to fix this soon because like I said it will be fine when I leave the house and then start acting up later. Sometimes a few days will go by then start doing it. Also when its acting up you can't do the "pump bump" it just does not run. Any other time its fine. This sucks because this was the same symptoms my last pump had so there might not have been anything wrong with the last pump. Do you guys see anything wrong with running the pump from another 12v source as long as it runs only when the engine is running? There has to be other people out there running a similar setup.

 

[JLandry]

If I wanted to bypass the ECM for right now do you know what I could hook it up to that has 12v ONLY when the engine is running?

I'll have to check out the wiring diagrams. There are of course many circuits which can provide power when the ignition key is in the run position, but the problem with using one of those is the lift pump would produce full pressure as soon as the ignition key is turned on and this could cause starting problems. Apparently the VP44 injection pump doesn't do well starting the engine when supplied with high fuel pressure, therefore the ECM operates the lift pump at a reduced duty cycle when starting.



I'll get back to you with more on this after I take a look at the wiring diagrams.



Best regards,



John L.

 

[nuv22]

correct I have read in the forums about people having problems with the pressure and hard starts or the truck not wanting to start with 16 psi but isn't there something in the vp44 to regulate fuel pressure ? i know there is a diaphragm that causes problems, I read about it in the installation manual for the fass it reads:

A small percentage of our customers have experienced hard start issues when placing our pumps on trucks with
The VP44 injection pumps, these pumps are found on 1998. 5 - 2002 Dodge Cummins pickups. The hard start issues we
incur are only found on this application. The hard start issue would occur with any fuel pump putting good flow and
pressure to the VP44 after the injection pump has experienced 5psi or less in fuel pressure. A VP44 receiving less than 5psi
in fuel pressure will more than likely be damaged, creating the hard start issue with good fuel flow and pressure. Please
read the following if you experience the hard start issue.
Hard Starts
Usually the FASS only encounters hard starts on the 1998. 5 - 2002 Dodge Cummins with the VP44 injection
pump. If this occurs it is usually on a VP44 with high mileage, and/or a VP44 that has been subjected to around
5psi of fuel pressure or less. It is more likely to occur when the weather is warmer/hot.
Explanation of Diaphragm: The diaphragm in the VP44 is designed to move about . 5mm with proper fuel pressure
(about 7psi min. ). When the VP44 is subject to about 5psi or less the diaphragm can move up to 2mm, an increase
in movement of 4 times more than what it was designed to move. With this type of movement the diaphragm will
eventually develop stress cracks thru out the body of the diaphragm. One job of this diaphragm is to separate low
fuel pressure and high fuel pressure in the housing of the VP44, when the cracks are present this separation does
not occur. This will lead to hard starts even with a stock OEM lift pump!!

Note: Not all failed pumps with broken diaphragms will start with low to no supply fuel. Sometimes the
diaphragm is so broken that charging pressure is not able to build to a level that allows the pump to deliver fuel.


Here are some solutions:

2. On our WH-1002 harness, cut the red wire between the FASS relay and engine harness. Splice a
length of the same gauge wire to the red wire coming out of the relay. Relocate this wire to a
fuse that is hot only in the “Run” position. An example is the Power Window or Windshield
Wiper fuse. This will cut power to the FASS when cranking.

So what gives? I supplied 12v to the pump for testing purposes and had my brother crank the truck and it started just fine with over 15 PSI on the gauge. Will this damage the vp44? If I use a relay and tap the window motor or the wiper motor so the pump runs only when the key is on the "run" position? I am just a bit confused because of conflicting posts.

John
Thanks again for taking time to reply.

 

[JLandry]

correct I have read in the forums about people having problems with the pressure and hard starts or the truck not wanting to start with 16 psi but isn’t there something in the vp44 to regulate fuel pressure ?

Yes... the VP44 is supposed to regulate its own internal pressure.



Your FASS research seems to indicate it's only *some* VP44's that have problems with starting under high (15 psi and above) pressure.



If your own personal testing with a jumper found no problems with starting, then go for it! You certainly won't hurt your VP44 by subjecting it to 15 psi pressure while starting. Low pressure is what kills it.



Definitely use a relay though.



Please keep us posted on how everything works out.



Best regards,



John L.

 

[nuv22]

yeah just wondering now how many people actually had this problem instead of a dead lift pump. i wonder what would cause the ecm to output low or no power to the LP just seems odd that everything else is ok, no codes nothing but the LP voltage acting up. I left my batteries disconnected over night to see if that helps before doing the rewire so far so good just drove it around and stopped at 3 places shut it off then back on and still good. so i will test it out this week when i drive to work and will let you guys know the outcome. i will go get the wires and relay to have all ready to go just in case it starts acting up again. if anyone has any other ideas or knows anything else about this problem please help.

Thanks

Raul

 

[EagleEye]

I just ran into this last week. I have been running the SAME stock lift pump with a Carter pusher near the tank for about 120,000 miles now. Going to work, the fuel PSI dropped to about 4 at idle and 0 to -1 while going. I figured the front stock lift pump finally gave up the ghost.



Drove the truck home and proceeded to change the stock lift pump... still low PSI, and I didn't see anything wrong with the LP I just removed. AND my rear lift pump had power. Cleaned connectore. Changed the rear lift pump, same problem. Changed ALL filters, same problem.



NOW... it was either a collapsed fuel hose, or the front pump just wasn't getting power. Ground was good.



Long story longer... power from ECM was getting to the soldiered patch for the rear lift pump, BUT was NOT getting to the front lift pump Deutch connector. The stock wiring harness wire that curves to the LP right before the Deutch connector had flexed and broke the internal wire. All looked good until I cut it out and replaced it.



Yep... the stock wire had gone bad from the shaking of the mighty Cummins. It just flexed enough over a long time to kill it.



CHECK power before pulling your hair out! The wire may just be bad. I couldn't tell until I tested it and cut it out. The wire is still on my bench.

 

[JLandry]

CHECK power before pulling your hair out! The wire may just be bad. I couldn't tell until I tested it and cut it out. The wire is still on my bench.

Raul,



This is a great post from EagleEye. If your lift pump acts up again due to low voltage, you might want to try "back probing" socket numbers 15 and 35 at the ECM connector on the engine wiring harness (see attached graphic). You can do this by carefully sticking a paper clip into the backside of the connector where the wire goes in. Alternatively you can pierce the wires with a sharp multimeter probe.



The wires you want to test are yellow with a white stripes. The two wires exit the ECM connector and join together somewhere in the wiring harness prior to the lift pump's Deutsch connector.



If you find nearly 12 volts at the ECM connector, then you'll know you have a wiring harness problem. If you find low voltage at the ECM connector, then presumably the ECM has an internal problem.



And as far as the ECM being at fault...



I don't find this an impossible scenario. After all, think about the heat cycling and shaking it's subjected to, bolted right to the side of that engine? I'm amazed they put it there in the first place!



Best regards,



John L.

 

[nuv22]

Ok I posted earlier but it did not show up. Thanks guys for the info and diagram. I went ahead and disconnected the batteries over night to reset everything before wiring in the relay and so far so good. I will test it out this whole week and keep you guys updated if the problem comes back. Right now I am dealing with a leaking ac line on the truck. Turns out the vibrations from the mighty cumminapart wore a hole in my ac line #@$%! So I am taking it all apart today and putting the new lines in. I know some guys are doing an ECM dissection I wonder if they might have any info on why the computer would send low voltage or no voltage to the LP when the engine is running?