Fuel pump cutting out

[peter cain]

So this is a weird one. 2011 2500 5.7. Been running great ever since overhaul some 4 years ago. It just started this wierd behavior where it seems like the fuel pump won’t run if system voltage drops below 11.5. Has anyone run into this? Symptoms would be: cold morning no start. Starter motor cranks engine smartly. jump with a jump pack or another vehicle, starts just fine. Once running, it runs fine all day. Re-starts, errands etc. no problem. I just installed a new battery today, so tomorrow we’ll see. Anyone run into this before?

 

[RedSRT4Me]

So this is a weird one. 2011 2500 5.7. Been running great ever since overhaul some 4 years ago. It just started this wierd behavior where it seems like the fuel pump won’t run if system voltage drops below 11.5. Has anyone run into this? Symptoms would be: cold morning no start. Starter motor cranks engine smartly. jump with a jump pack or another vehicle, starts just fine. Once running, it runs fine all day. Re-starts, errands etc. no problem. I just installed a new battery today, so tomorrow we’ll see. Anyone run into this before?

Yes. It's part of the safety features of the vehicle. If the voltage gets too low it will cut power to save the PCM. I guess it's possible to short the PCM with a consistently low voltage over time.

 

[peter cain]

Yes. It's part of the safety features of the vehicle. If the voltage gets too low it will cut power to save the PCM. I guess it's possible to short the PCM with a consistently low voltage over time.

But 11.5V? I hear what you’re saying, it’s just that 11.5 seems a very high threshold to me.

 

[jws123]

Sounds like you need to check your battery however i have started my truck with a nealry dead battery before so....

 

[RedSRT4Me]

But 11.5V? I hear what you’re saying, it’s just that 11.5 seems a very high threshold to me.

Yes. 11.5v. I unfortunately had a cut accessory belt that would start the truck but once the alt charge dropped to 11.4 the truck shut off. Of course I needed a jump to get the battery back. A new belt installed and back in business. I would caution those who have 3+ year old batteries, something like this may kill it for good.

 

[peter cain]

Sounds like you need to check your battery however i have started my truck with a nealry dead battery before so....

I thought I had too, but apparently not…(?)

 

[peter cain]

Yes. 11.5v. I unfortunately had a cut accessory belt that would start the truck but once the alt charge dropped to 11.4 the truck shut off. Of course I needed a jump to get the battery back. A new belt installed and back in business. I would caution those who have 3+ year old batteries, something like this may kill it for good.

That sounds crazy to me. My truck is obviously acting that way, so I don’t have much to argue with. What do you mean “kill it for good”?

 

[RedSRT4Me]

That sounds crazy to me. My truck is obviously acting that way, so I don’t have much to argue with. What do you mean “kill it for good”?

Meaning the battery is unrecoverable

 

[peter cain]

Closing notes:
Ultimately my issue was the fuel pump relay embedded in the TIPM, which, according to anyone you ask, is a real common problem . It finally showed a hard failure; something I could really troubleshoot. The fuse showed no voltage, and since that’s after the relay, that’s all I needed to know. I made a hinky cable out of a couple “add a tap” things from Napa, and the pump is now running off the cigarette lighter circuit. This is only until I can get in there and install an external relay that is driven by the PCM. That kit used to be made by Mopar, but it’s apparently discontinued for some dumb reason. No biggie. It’s not hard to make. Anyway, I’m running for now!