bc3

Ok, heres my question: does low fuel pressure equate to the possibility of lower fuel economy?

I have been chasing this lower than normal fuel economy for some time now. My truck is all stock and has been due to not wanting to jeopardize my warranty...but at 40k miles now, this mileage thing is forcing me to look at other options.

anytime you read about lift pump systems from Fass etc they say it "HELPS" fuel economy..so that means a stock liftpump that perhaps is lower than norm pressure (but not throwing a code) may be the culprit?

This all started when I added a Commander guage assembly..my idle pressure reads norm 4-5 at idle and 4pis driving at <40mph. If I step on it and get my rpms up to 2k, the pressure drops to 2 (no load ). Ive never had any issues to date except that the truck feels sluggish to me. I have been testing out a new smarty and mileage has gotten worse on level 3 with the stock and beta programs. AT the very least I was hoping for better and not worse.

I am going to make up a mechanical guage and test it against the commander for accuracy; the fuel filter is brand new 10 micron ( I know it is supposed to be 7, but its all they had in stock), the commander calibration parameters are all correct. I dont know what the normal pressure range is. I have an 04.5 5.9 auto srw slt 3.73 and think I remember reading about a factory lift pump TSB update that moved it from the motor to the tank...is this an issue?

thanks! bc3

CamperAndy

What is the actual MPG that you are getting. It may be normal and you just have too high expectations.

XLR8R

I think the FASS helps economy by separating air out of the fuel - helps the injectors to work more efficiently.

Your truck has the filter-mounted LP, which has been superceded by Dodge with the superior in-tank LP.

I can't see how lower LP fuel pressure will help mileage.

Can't you pull the LP psi down to zero with the Smarty?

kingofdodge7131

It has some effect on mileage, just like if you have a clogged filter and your mileage goes down because the fuel pressure is too low

CD in NM

Actually, it may be more about volume rather than pressure, but it takes pressure to make volume.

You would probably see some immediate mpg difference if you went to an in-tank lift pump. I believe that many here have discussed better mpg gains after their original pumps finally failed and the dealer replaced them, under warranty I believe also or that tsb?? Not sure, someone will comment/correct me I'm sure.

I have a friend with a 2004.5 and his pump went bad, dead on the side of the road-flatbed trip to the dealer. He told me that they replaced his pump with an in-tank pump and his mileage went up. Since I am not familiar with where the pump was locate (might have been at the filter housing??) anyway, he reports better fuel mileage AND what appears to be a power gain. The power gain only makes sense if it had insufficient fueling. Also, this was covered by his warranty.

CD