Chevy and GMC Duramax Diesel Forum banner
1 - 12 of 12 Posts

· Registered
2021 AT4 3.0 Duramax
Joined
·
71 Posts
Discussion Starter · #1 ·
For all of you that have an Idash or CT3, what is the lift pump pressure you guys are noticing?
Since the beginning of winter, I’ve been noticing the pressure on my truck upon start-up is around 85-90psi before it settle downs to 65-70 after full warm up.
Not sure if this is normal. Changed the fuel filter at the beginning of winter.
Thanks
 

· Registered
2021 AT4 3.0 Duramax
Joined
·
71 Posts
Discussion Starter · #3 ·
Thanks for the reply.
Yes I remember my truck being around 60 as well. Also threw a CEL P#2635 this early morning that confirmed my suspicions.
I think the pump is failing and the -30C weather we are going thru is doing any favours.
Thanks again
 

· Registered
2022 Chevrolet 3500 High Country CC
Joined
·
1,424 Posts
This comment relates to the L5p's but may be similar, I know the filter housings and fuel filters are the same, not sure about the lift pumps..

The L5p's will increase the fuel pressure on key on and startup to force fuel circulation to warm the fuel in cold weather conditions. Something to keep in mind is the factory fuel filter has a differential burst pressure of 90psi and the pressure sensor for the low pressure side that controls the lift pump is after the filter. The in tank lift pumps are capable of 100+ psi.

With that said if you see it above 90 much less close to or above 100 checking and replacing the filter may be worth while. Because the pressure sensor is after the filter if the truck calls for say 80psi to warm the fuel and the filter is restricted it can produce in excess of a 100psi from the pump, if it can't flow through the filter it could rupture. There is another thread on here from a gentleman from last winter with his L5p and it didn't want to start, he came to the conclusion that a gel event clogged his filter and the dealer discovered the filter had ruptured and blew dirt and chunks into the engine fuel system, 10 grand later he got his truck back.

So yes, if the 3.0 fuel system is similar to the L5p then higher fuel pressure on lift pump is normal to assist in warming the fuel and clearing any minor cloud or gelling of the fuel.
 
  • Like
Reactions: Reddy and Piper One

· Registered
2021 AT4 3.0 Duramax
Joined
·
71 Posts
Discussion Starter · #5 ·
Thanks for the reply @Satar.
Yes the way you put it makes sense from my observations over the last week.
When it’s 20C below, the pump stays around 80-85 for longer then drop to 65-75.
Now it has warmed up a bit to 5-10 C below, it stays high only for a few minutes.
Out of caution, I drained the filter. There was no water or debris.
I had to visit the dealer for a different reason, and the tech cleaned the connector for the fuel pump and said the pump is operating as it should be.

Thanks again
 

· Registered
2021 AT4 3.0 Duramax
Joined
·
71 Posts
Discussion Starter · #7 ·
It is an observation.
It did threw a code P2635. Pump A low fuel flow, which made me weary. Technician cleaned out the electrical connection and turns out that’s all it was. Fuel pump is working as it should be.
It seemed abnormal as the fuel pump would make louder than normal noise upon cold start.
BTW what it the lift pump pressure you are seeing?
 

· Registered
Joined
·
7,836 Posts
Was out with it today and thought about this thread, so changed idash to show lift pump and it always ran 64 - 67 range .
Mostly 64.

When cruising at 55-60 and then accelerating sharply, lift will drop -- but during that event the rail pressure and boost pressure both double what they were reading at steady speed. Lifting to return to cruise speed and all go back to previous values.

Didn't think about it before cold (27F) start-up so don't have 'cold info'.

@Reddy , what does your rail pressure do at cold start? How about boost when this is going on?
 

· Registered
Joined
·
1,323 Posts
Should have stared mine a week ago -20F probably has straight #2 in it. Would have been a good test.
 

· Registered
2021 AT4 3.0 Duramax
Joined
·
71 Posts
Discussion Starter · #11 ·
Hey fellas
Thanks for the replies.
@redwngr ; it seems like the lift pump pressure goes up when the fuel temp dips below 8C.
The fuel rail and boost going up or down is not effecting the lift pump pressure much, at least when it is as cold as it’s been today.
Especially when cruising on HWY in -20C weather, the fuel temp gradually drops to/below 8 and I see the lift pump pressure go up and come down once the fuel temp reaches 9. Despite this, I could not pick up on any other parameters that correlate.
Vehicle Speedometer Automotive lighting Hood Motor vehicle

Vehicle Hood Car Automotive mirror Automotive lighting

Land vehicle Vehicle Automotive lighting Automotive mirror Car
 

· Registered
Joined
·
7,489 Posts
If you monitored the pressure in the transmission you would also see higher pressures when cold and lower pressures when hot. Nature of the beast.
 
1 - 12 of 12 Posts
Top