I think the lift pump in my 94 Cummins engine is a mechanical pump, aren't they all mechanical?

Sorry if this is a dumb question.

I have a guy with one of my Cool-down timers inquiring "why his fuel pressure gauge is dropping to zero psi when the key is removed and the truck is running on the timer". He and I are thinking, it could be the power is removed from fuel gauge. The other option could be the power to the lift pump. Thus my question.

Thanks for this web site and the great help found here.

 

The 12valve engines have a mechanical pump. As long as the engine is running, it is pumping.

 

There is no such thing.

 

If the guy inquiring has a 98.5 on up he has an electrical lift pump.

 

If it's newer than 98.5 it's an electrical lift pump. It's no good idea to let an engine run withou the lift pump on. (It would be very detrimental if you placed a load on the engine)
The lift pump is controlled by the PCM, I think you should override it with a separate relays for the cooldown timer.(I assume that you don't emulate the engine run key position with your timer since the LP seems to be stopped)

Just my 2c

AlpineRAM

 

I have an email out asking what year truck he has, but from what you all have said, I think he should be OK. So then, if it is older that 98.5, he is OK and if it is newer than 98.5 it should be OK because I am powering up the PCM and that should apply power to everything the engine needs to run properly.

As I sugested before, it must be the fuel gauge power.


Thanks again,

-- Man I love this place.

 

AlpineRAM thanks for your feedback, I do power up the "run key position". So the LP should not be the problem, right!?

 

If the key is in run and he has powered his gauge stuff from accessory this behaviour makes sense. (Simple way to check would be using a mechanical FP gauge like the Briar hopper one)

AlpineRAM