Help: Fuel milege

[mybowtie]

My fuel milege keeps dropping! I`ll take her on the freeway and depending how far I go she normaly gets 16.5 to 18.5mpg which I thought wasnt anything to brag about! and when I get back to town the milege keeps dropping anywhere from half to a full mpg a day! I dont get it last week she was down to 11.3 and befor I owned her about 6 months ago I saw the gage at 9.8 whats goin` on any one know????? She Just got her 100000 mile tune up 2 months ago!!!

 

[TeaBagger2006]

...bad fuel??? But seriously I've never gotten good mileage out of my pig. 12-13 mppg drving around town and 17 on the highway.

 

[DAVe3283]

What speeds on the highway, and what tune/wheels/tires do you have? Also, how heavy is your truck?

I get about the same highway mileage as you when doing 65 - 75 MPH, and as low as 13 in town. I would probably get a lot worse if I actually gave it some power in town.

So if your truck is similar to mine (weighing in at a measly 8000 lbs, 285/75R16 tires on heavy rims), that might be normal. But if you have a lighter truck, and/or narrower tires, you should probably do better, at least in town. Try a new fuel station?

Edit: you're not believing the display on the dash, are you? Because after a year of tweaking the DIC correction table, mine is only within 5%. It was farther off than that from the factory, sadly. You have to hand-calc the mileage to get meaningful numbers.

 

[mybowtie]

Everything is stock on my truck next time i fuel up im fixin to put an additive in too! I just bought this truck from the owner of the park i work at and I dont think he ever has!!

 

[AdaMax]

a friend of mine was getting badfuel mileage . His cp3 was bad so he replaced it ( purely for the hp not the mileage ) and it helped his a bunch . Of course it went through a lot of abuse too but basicly the same mileage .

 

[mybowtie]

Whats a cp3? Im new at this! Well the guy I bought this truck from never spent the time that I do to even wax her befor I got her a couple of months ago and he bought her new in `06 if that tells you anything!

 

[JoshH]

The CP3 is the high pressure fuel pump which is mounted in the valley. It supplies high pressure fuel to the fuel rails that feed the injectors.

 

[mybowtie]

got ya, but whats the valley? your talkin to a newbee with deisels!

 

[JOE]

under the oil pan, keep looking

 

[dieselboy04']

So would having water in the fuel hurt the cp3 to the point of bad fuel milage?

 

[JoshH]

got ya, but whats the valley? your talkin to a newbee with deisels!

The valley is at the top of the motor between the heads (same as any V configuration engine, BTW).

So would having water in the fuel hurt the cp3 to the point of bad fuel milage?

The reason a bad CP3 can hurt fuel mileage is because the drop in fuel pressure causes the fuel to not atomize correctly and is more pronounced under a load. If you aren't having rail pressure issues, you probably didn't hurt the CP3.