Lift pump won't shut down

[BoeingDiesel]

Went out to drive my '99 this afternoon, and as usual, I always bump the starter one time and wait for it to cycle and then start the truck. This time, the lift pump took about 20 seconds to activate and then it wouldn't shut down and I finally had to unplug from the harness. I didn't go any further as this can't be right. Any ideas, suggestion etc are greatly appreciated.
thanks gregg

 

[DavidC]

Factory stock configuration through the ECM and nothing else added ?

 

[BoeingDiesel]

Nope...bone stock. I read on another forum that the PCM contains the lift pump relay...not sure that's trustworthy though.

 

[petersonj]

Have you owned the truck since it was new? If so, then as @DavidC says, the ECM supplies 12 volts directly to the lift pump. Normal operation would be as follows: key in run position - lift pump runs for less than 2 seconds, key in bump start and then left in run position - lift pump runs for about 20 seconds.

I have owned my truck since it was new. Under warranty at 87,000 miles the VP44 was replaced and an in-tank lift pump with a relay controlled by the ECM was installed by the Dealer as a fix for lift pump problems. If this conversion was done to your truck, then you will have a lift pump relay.

- John

 

[BoeingDiesel]

I took delivery of the truck in August 1998 and never converted to the in tank lift pump. If the ECM is the culprit I would think it would throw a code?? Worst case scenario I can hard wire to a in cab switch as others have done. I'll check for voltage from the ECM today but at this point I'm not real optimistic but I'll post what I find or remedy as it may help someone else down the line.

 

[DavidC]

The lift pump is powered through the ECM and appears the electronics shorted. The wiring is fairly short as the ECM is close to the pump. You could try disconnecting the batteries for a while, maybe the ECM had a hiccup and thinks the engine is running. I do have a switch on the bottom of the dash used as an override for mine when the pump did not run. Guess you could wire in a off delay relay that times out when the ignition switch is off and shuts the pump down. Friggin electronics.

 

[petersonj]

@BoeingDiesel, if you decide to modify the lift pump wiring circuit, be sure to include a means to shut the lift pump off in case the truck was involved in a serious accident. For example, you could add a relay that would be controlled through an engine oil pressure switch.

- John

 

[DavidC]

Or you could go this route

 

[BoeingDiesel]

All good information and I appreciate your feedback. I disconnected the batteries and will let it set for a day or so and see what happens.
Who knows...might save me a grand! I read John Landrys' post on the https://www.cumminsforum.com/forum/98-5-02-powertrain/473649-lift-pump-wont-come-my-99-a-2.html.
Very similar symptoms and I may try the " Alternate lift pump circuit" he posted. Which reminds me...I haven't see a post by John in years. Whatever this turns out to be I will post it here.

 

[BoeingDiesel]

I disconnected the batteries for about 22 hours and reconnected and the truck starts and stops like normal. Maybe it has something to do with not being a daily driver and age?...I don't know and odds are it will do it again. Friggin' "A" model 2nd Gen electronics are a PITA and had it not been a Cummins would've gone bye bye years ago. Enough of my rant and thanks to all for your feedback. gregg

 

[DavidC]

Well that's great news. So the ECM had a hiccup.

 

[BoeingDiesel]

Well that's great news. So the ECM had a hiccup.

It would seem so. Ultimately, the '99 will be moved to our TX. dirt and be an off highway truck only.
DavidC, I have another source for your list of ECM issues. Good reviews and spoke with them this morning.