Engine/Transmission (1998.5 - 2002) Intermittent lift pump?

[hsmith]

This truck, '99 auto 4X4, does not energize the lift pump when the key is turned on until after 5 or 6 seconds if at all. Also, when I bump the starter, the pump most of the time will only run for a couple of seconds. Of course while this is going on, there is no start. When I bump the starter and the pump runs for the 30 seconds or so like it is supposed to, the truck starts fine.



I know the pump is supplied voltage by the PCM. That must also be where the pump relay is. My thought is a faulty PCM.



Everything else works fine. I am tempted to run the pump off a separate relay ignition fed bypassing the PCM.



Your thoughts

 

[JLandry]

Greetings,



The lift pump is controlled by the ECM (Engine Control Module) not the PCM (Powertrain Control Module). The ECM has internal solid state relays to control the lift pump operation.



If the lift pump does consistently run, but not always at the correct time, then you can probably rule out any problem with the relays in the ECM. Rather it could be a problem with the ECM's software or some other internal component failure.



Do you know if the ECM software has ever been reflashed?



If not, it can be done in the truck with a Chrysler DRBIII Diagnostic Scanner or by an after market power programmer such as those from Hypertech or Smarty (by simply uploading the power program and then returning the programming to stock).



Best regards,



John L.

 

[hsmith]

Thanks John,

This one most times will not run when you cycle the key, sometimes for a few secs, sometimes will run for about 10 secs when you turn the key off.



Think I am going to put it on a separate relay and energize it from the switch. This way it will run all time the switch is on.

 

[BEnglish]

Hey there in the hill country…I was there weekend before last at K-rocks (rock crawlin' Texas style) in Ketemcy, in between Brady and Mason.

Any way…I will be watching this thread as I am having the same trouble:

here is the link to my thread

I may end up going with a relay too, then I can add a hidden togle switch inside the cab that kills the lift pump as a security measure.

Good luck.

Ben

 

[Rattlin_Ram]

Killing the lift pump would NOT be a good security measure IMHO. The truck will still run without a lift pump, it'll just burn up the VP44...

 

[hsmith]

Glad you spent some quality time in the Hill Country. A little farther SE to the Kingsland area is as good as it gets.

 

[hsmith]

We're not talking security here, just trying to make it run. The "switch" I am talking about is the ignition.

 

[hsmith]

So this '99 uses both ECM & PCM?

 

[JLandry]

So this '99 uses both ECM & PCM?

Yes.



The ECM is located on the side of the engine. It's primary job is to control the engine and the new electronic (compared to previous Cummins engine with a mechanical fuel injection) VP44 fuel injection system.



The PCM is located over on the passenger side of the firewall under the hood (behind the air cleaner box). It's primary job is to control the transmission, charging system, and cruise control.



In most other Chrysler vehicles without a Cummins diesel engine and electronic fuel injection, there is no separate ECM for engine control... the PCM takes care of this function on most vehicles.



Back to your intermittent lift pump problem...



It sounds like you either have a wiring harness problem or a malfunctioning ECM. Have you tested and eliminated the wiring harness as causing the problem?



Best regards,



John L.

 

[hsmith]

Thanks again John, looks like this is an ECM issue for sure.



Smitty

 

[JLandry]

Smitty,



Rather than buying a whole new ECM just for this issue, you should have no trouble hooking up a separate ignition switch controlled relay to energize the lift pump instead of using the ECM. I've read here on the forum where others have done this and they reported it worked fine.



Just be sure the circuits are protected by fuses.



Best regards,



John L.

 

[AdamH]

The intermittent operation of your lift pump you described is exactly what my pump was doing when it started going bad. I replaced the pump and the problem went away.
Adam

 

[hsmith]

Did just that John. Fused relay wired into the ignition switch for the pump.



Engine will not start until the WTS light goes out. Guess the ECM waits that long to energize the FCA.



Also installed a low pressure warning lamp on the dash for future fuel pressure problems. May help prolong the life of the VP44.



Thanks again

 

[Andy Redmond]

Smitty:



I hope you didn't hock your 12v. !!



Monitor Pin 7 from this post

https://www.turbodieselregister.com...ne-transmission-1998-5-2002/205705-p1693.html



s/b 12, trace it back thru the pin 87 at the fuel injec. pump relay in the pdc, pin 30 of the relay is B+, pin 85 is the grnd, and pin 86 closes the relay to complete the circuit, pin 86 goes to pin 36 on the ECM harness (behind fuel filter).



See attachment for ECM pin out. you will notice that ECM pins 15 & 35 power the transfer pump. The 1998 FSM, ch 14 provides some good reading on how the transfer pump works, one of the pins should provide voltage drop during cranking only for easier starting, the other 12v to operate the transfer pump while engine runs.





I changed an ECM recently for a concern of the engine shutting off after it warmed up. I found no/low voltage after engine heated up on ECM pins 36, 15 or 35 (actually too little voltage, it would drop to to 7 volts and the relay coil would open in the pdc, and the truck would die).



FWIW I don't change out ECM's very often, but lots of VP 44, IP and LP and wire harness repair.



Hope this helps.

Andy

 

[hsmith]

Hey Andy, I am bringing this open again. Customer took the truck and all was fine for a couple of months. Then he called me from San Antonio and said he had a no start. Pump running just would not start. Had it hauled to me on a roll back, thanks to AAA's expense. Unloaded the truck and it fired right up. Needless to say, he has no faith in it now. Guess it is time for an ECM. Do these have to be flashed for the truck to run or they plug and go? Is my best bet for one from the dealer?

Thanks again, and to answer your question, the old 12 valve is still a part of the family and running pretty strong too.

Smitty

 

[SnoKing]

Put a new lift pump on it! SNOKING

 

[JLandry]

Pump running just would not start. Had it hauled to me on a roll back, thanks to AAA's expense. Unloaded the truck and it fired right up. Needless to say, he has no faith in it now. Guess it is time for an ECM. Do these have to be flashed for the truck to run or they plug and go? Is my best bet for one from the dealer?

Smitty,



If I understand the situation correctly, the lift pump runs, the starter cranks, but the engine doesn't always start... yes?



If so, have you tried replacing the ASD (Auto Shut Down) relay which is located in the PDC (Power Distribution Center) on the driver's side fender under the hood? This plug-in relay is of the common size and configuration found in the electrical section of any auto parts store, so no trip to a dealer should be needed. If that relay is intermittent it'll cause symptoms *exactly* as you describe. For temporary testing, you can simply swap it out with another good non-essential relay like the wiper or horn.



Another relay to check or replace is the one labeled "fuel pump" or "fuel injection. "



I doubt it's the ECM, but to answer your questions...



You can order a generic refurbished unit from a dealer and it would have to be flashed using a DRBIII scan tool with the proper software after installation. Dodge stopped selling pre-flashed ECMs and PCMs some time ago.



A better (cheaper) alternative is to buy a refurbished unit from Auto Computer Exchange in Florida. They'll ship it to you pre-flashed with the exact software needed. I've purchased both an ECM and PCM from them over eBay, they worked perfectly, and I verified (using a DRBIII) that they indeed had the correct software installed.



Good luck,



John L.

 

[RJWEST]

I think I'd wire a voltmeter to the ecm lp output too see if it is really an ecm probllem.



Also , whats the REAL voltage at start up, sounds like bad wiring

somewhere, maybe a battery terminal/wire causing low voltage when heater grids are on

 

[Andy Redmond]

Hi Smitty:





The first thing I would try is a basic elec. test of the batteries and charging system including how low OCV is when cranking. Low voltage will drive a ECM/PCM crazy.



Also ck. the grounds. An intermittant ground can also cause you fits.





John provided excellent advice. & RJ provided excellent advice. Look at my post above for pin outs etc.



Remove the fuel filter and get your DMM out and some lubricated (small) sewing needles to back probe the connector on the ECM... you should be able to replicate the fault if its the ecm.



Get a pan under it in case the lift pump comes on. . you can temporarily bypass the fuel filter with a piece of 3/8" SAE 30R7 hose (lift pump to injection pump) if you have a couple of barbed banjo fittings. (so it doesn't make a mess). . remember, unfiltered fuel is going right into the pump, so a pan might be a better alternative.

 

[hsmith]

Hey, thanks to all for the info. Getting the truck back Monday and will do the tests. Will get back with results, and probably more questions.