Engine/Transmission (1998.5 - 2002) Lift Pump Power

[speedo81972@yahoo.com]

My truck won't start, found the lift pump not putting out any pressure. Changed the pump (foolish mistake) without first checking voltage to the pump. I'm only getting 8.6VDC to the pump. The manual says that the ECM controls the lift pump, but I would think that would be an on/off thing. I didn't see anything in the schematic that would restrict voltage. Checked all the grounds and connections, everything is tight. Am I looking at replacing the ECM or can there be another cause? It's a '99 with 130K, MBRP 4" exhaust, Airaid intake.

 

[SnoKing]

Some reading! SNOKING

https://www.turbodieselregister.com/threads/217584-Voltage-readings-at-lift-pump-lead

 

[RikDavis]

just a thought after reading the other thread. It would seem that a 6 volt relay could be powered by the sick ECM and that could key the 12 volts for the pump. That way you would retain the duty cycle timing

 

[speedo81972@yahoo.com]

Latest update. I jumped the lift pump straight from the battery, bled the injectors and truck started fine. Voltage to the pump connector is 13+ volts when the truck is running. When I shut the engine down voltage drops to nothing when it should stay powered for 20 secs. I put everything back together, started the truck and everything seems fine, when I shut it down I can hear the pump still running. Kind of at a loss, because I don't know if I can trust it. Still looking at an ECM. If I can get it to a Dodge dealer I'll have them put an analyzer on it.

 

[WardJ]

Best of luck with this. I think I would try the 6 volt relay first before I bought the ecu. Of course, I'm a cheapskate.

 

[speedo81972@yahoo.com]

This may sound strange, but I think changing the alternator cured most if not all of my woes. While I was scratching my head and trying to figure things out I noticed my alternator screaming like a banshee (another new ailment). After changing it everything seems to be fine (for now). The alternator was putting out 14.2V, but I'm not sure how clean the power was going to the computers. I will be closely monitoring the engine, I should probably change the VP44 soon, since it's the original, and with everything else that's happened it will probably die in the short term. Greatly appreciate all the advice and help.