I havent done any better than 400 miles to a tank no matter how nice I drive, this thing is not good on fuel by any means, the overhead says about 10 MPG, I know I have mods and it's winter but isn't that horrible?? Is there soemthing I can do is there a reflash or something??? Even if I completly fill the tank and reset the overhead it says I will get estimated 356 miles to empty?? What the hell is going on can anyone help or at least tell me this is normal.

 

How do you drive it ? Idle time ? Speed ?

Check rail overpressure relief valve, lift pump, CP3.

Have you done the tone ring mod ?

Is it lifted ? What did it get for mpg before the mods ?

$20 says that your rail overpressure valve or CP3 is damaged.

 

While my 04.5 has never been real good on fuel, either, I have dropped about 1 mpg lately as well. Two things have contributed to this:

1. my CP3 is leaking for two weeks now (parts STILL on order at the dealer )

2. Winter fuel. This is the MAIN culprit. My PSD always lost 1-2 mpg on winter fuel.

 

how often does the cp3 leak? Sorry for the dumb question, but where is that located? I also get crappy mileage

 

Search the 3rd gen forum. There is lots there. Don't believe everything you read.

 

mine has been bad lately too, I am wondering if I should borrow a gps to use as a tripo meter to see if I have my tire calibration done correctly. I am up to a half a bottle of ps white bottle per tankfull, seems to rattle a little less but dang my bowtie gasser did better. I know its a truck but so was the gasser........... at this rate I will have to drive the truck 3.2593 million miles to recover the cost of the diesel option.

 

I think your air filter is drawing hot air from your engine compartment. It is right by the air flow coming off the radiator. Bad.

 

Want good mileage?? DRIVE IT

I havent had my diesel long, but long enough to know that this engine wants to run....Long, hard and fast....Running around town has gotten me no better than around 14....Every time I've had it on the highway longer than 30 miles its jumped up by 2-5mpg depending on length of trip, speed etc...

 

superduty, if you are saying mine is in the hot air stream considder this, I remover the side duct guide to the pass side of the radiator, allowing air to flow stright into engine compartment and to the are awith my bhaf, that and it being in the low 30's should let the cooler do its job and drop the charge temp low enough. I have thought about making a heat shield but in these engine bays the way they are so routed with wires and lines there is little room to do it neat, no way to get an old smokey setup in there and expect it to do much. If I ever go stacks they will be outside the bed and then the air cleaner will travel outside the body like the big rigs hang their air cans. just not renceck enough to do it yet.

 

I think it sucks hot air. Mine does too. (See my pics.) The air flow swirls around in the engine compartment. It isn't just straight. There is a reason the stock box is totally closed to the engine compartment.

It might not have much to do with things right now, given the air temp, but I bet it does in summer. Maybe the air is hotter in the engine compartment in winter due to the fan not running and running a winter front ?

You might have other issues too.

 

Are your numbers overhead or hand calculated ? Have you at least topped it off twice back to back ?
Did you have your pinion factor re-set to offset for the larger tires ?
Greg

 

What trans and gears? What type of driving? Where are you?

Winter fuel, cold temps, big tires, auto trans, stop and go driving are not a good combination. Any of the 3 are gonna cause low mpg. Ther is a flash for the early 600's for poor mileage and/or white smoke on startup. Might check into that but it may be a crap shoot if it will help.

Or move south. I picked up 2 mpg going to So Cal for Christmas. Lost it just a soon as I got back home.

 

I took mine in and had it reflashed and it went from 10mph to 16mph overnight.

 

Besides checking everything else that has been posted (especially the pressure relief valve as Superduty has stated) you might also want to consider doing the tone ring mod or installing the Rokktech sensor. It gained me mileage...but I didn't start at 10mpg either. How many KM on your truck right now?

 

I only have 38,000 KM around 23,750 Miles, do I have a ways to go before break in?? All these sensor mods, can you explain a little more??