Does the lift pump pressure effect MPG? I was getting 17.5-18 MPG city and up to 21mpg hwy. Now, at best, I'm getting 13-14 mpg city and hardly any better hwy. Truck is loaded the same as before, new fuel filter, tire pressure above 60psi. Truck has 88k on 1st lift pump. Lift pump pressure is 5psi at idle. Can't check it at other times, gauge screwed into top of filter housing. It is an oil pressure gauge, does that matter? Any ideas and suggestions ?

 

whoa had to stand back to read that.

 

Wow dude, tone it down a bit. If your lift pump is at 5psi at idle, it is time for a new lift pump. You are putting undue strain on the VP44, and you do not want to replace that unless you are independently wealthy!

 

Does the lift pump pressure effect MPG? I was getting 17.5-18 MPG city and up to 21mpg hwy. Now, at best, I'm getting 13-14 mpg city and hardly any better hwy. Truck is loaded the same as before, new fuel filter, tire pressure above 60psi. Truck has 88k on 1st lift pump. Lift pump pressure is 5psi at idle. Can't check it at other times, gauge screwed into top of filter housing. It is an oil pressure gauge, does that matter? Any ideas and suggestions ?

 

Sorry 'bout the size of text!!

 

I was getting the same idle pressure as you with 0 lbs. at wot. I changed the lift pump and my MPG got better.

Mark

 

Without a doubt, 5 psi @ idle = 0 psi @ WOT. Park the truck now and do not drive it until a new LP is installed or you will be sorry!!......and yes, you can expect a mileage gain with a new LP that feeds the VP44 the appropriate pressure.

 

I would say if a clogged fuel filter can make mileage go down, a lift pump not pumping well could also.

5psi at idle!?
You gotta be sucking it down to zero under load, change that puppy ASAP.

Another thing to check when mileage suffers is the IAT sensor.
http://dodgeram.org/tech/dsl/sensors/IAT/clean.htm

I'd also be checking the air filter just because.

That much of a drop, I'd also check the oil for diesel contamination, if you had a leaky injector that'd drop the mileage down.


phox

 

I would say that there is definatly something wrong with the pump. Your mileage should go down with a new pump, it should go up if anything. Some people have gotten new lift pumps that were bad. I would look into getting another one.

 

Replaced Lp this afternoon, all went well except for air in lines. After reading several posts on the subject, got it running- finally! 15.5 lbs at idle now....seems to have a little more power and if my ears don't decieve me, it's a little louder, a little more diesel clank. Found pump @ local Cummins parts store for $160.00 I'll let you know about the fuel economy when I know....