Anyone have any idea why my truck might seem to run better when im down to a 1/4 tank or less? Is is a weight thing. 2004 4.6.

 

What do you mean by "run better"?

 

The trucks just responds better, its like you hauled a trailer full of stuff with the top 3/4 of the tank of gas, then you dropped your trailer and ran the last 1/4 of the tank without a trailer. Thats sort of how it feels i guess.

 

I would start with your fuel cap, and lines. Sounds like a vent is plugged? Check your fuel pressure with 1/4 tank, and then top it off and do the same.

 

just based on the fuel weight, I can tell a slight difference when under 1/4 tank. I have a short work commute and only have to fill up my tank about once per month. So I might spend like a week or so at 1/4 tank or less, and I can tell it accelerates or "responds" a little quicker without the extra fuel weight.

gas weighs 6.175 pounds per gallon. So a 30 gallon tank of gas weighs 185 pounds.

 

You think it could actually be a problem, the difference isnt ezactly as drastic as the trailer analagy sounded, i can just notice that it runs different with less gas in the tank. Its not a problem, i just wondered cause it seemed weird to me. It sounds more like what SteveVFX4 said. But would a fuel cap do something like that?

 

i think its the amount of fuel in there...weight issue. i notice the same thing with my '08. i can smoke rubber with no brakes if the tank is less than 1/4 full...

 

Yes, but it should pop a code too. Did you change your fuel cap out recently?

 

No i didnt, its still the factory i believe. No codes, no problem, just curious, and it might just be the weight difference.

 

I don't notice a difference in mine when full, or at 1/4, and I have a 35 gallon tank Screw with a 6.5' bed. Maybe I'm just desensitized.

 

A gallon of regular gasoline weighs approximately 6.216# while premium weighs about 6.35#. Then a 35 gal. tank holds about 217.56# of reg. and 222.25# of premium. A 1/4 tank of reg. (8.75gal) weighs @ 54.4#. If there is any effect due to the amount of gas on board I don't think it is due to the 163# difference.

 

same here on my 04 screw

 

GEEZE; these are trucks and I don't think anyone could tell the differance in performance wether or not they have the girl down the road riding with them ( she weighs more than 30 gals. of gas ) some of these answers remind me of fat girls husband who claims ; after CAI & cat back exhaust " that truck really goes now" which is plane stupid. Gains like this can only be measured in tenths or hundredeths of a second in a 1/4 mi. NOT by the seat of the pants

 

A more reasonable explanation would be SUN SPOTS or MOON PHASE

 

You're sure to have the CAI owners after you now. I like the sound of a good exhaust though. I might get a new muffler, just for the sound.

YOU'RE A MARKED MAN NOW!!!!...lol