Unbelievable mileage
 

I have a 99 f-250 , but I put a 5.4 liter from a 97 expedition. I took out all the EGR crap because I read you don't need it, Its got a nice lift and big tires and it runs simply beautiful with tons of power, but I an getting an unbelievable 5mpg. not towing or carrying anything. I cant find a leak but it does smell like gas. When I get out. I have K and N filter and I have malfunction code for one of the o2 sensors but I don't think that's enough to get this bad of millage.

EGR removed with no tune and a code for o2 sensor, 5 mpg is believable under these conditions.

What else did you remove along with the EGR? The computer should be throwing codes about the egr and other stuff.

You really shouldn't remove the EGR and other emissions equipment unless you are prepared to get a programmer and custom tunes to compensate. The stock tune is set to optimize with the presence of all the mandated equipment. It WILL run excessively rich with no EGR.

Please post all numeric OBD2 codes. If it smells like gas, you have a leak or it's running way too rich. I'd put all the stuff back on that you ripped out. What you read is incorrect. What you read is for old pre-computer carbureted engines.

I'd also get rid of the K&N and put a paper filter in. The oil on the K&N can foul the MAF sensor, and it also lets a lot more fine dust in than a stock filter.

Not sure If it was a type-O error or not on the OP. If they meant F150 or as posted the F250
Anyway didn't think the F250 had the EGR??

All 5.4 2 valves have EGR. 3 valves do not.

Unbelievable Mileage
 

I think I figured it out, this supposed "mechanic' who was helping me hooked up the gas delivery system wrong when I wasn't looking. Mixed up the lines and fed half of the gas into the back of the throttle body, where the gas vapor line was supposed to go, I'll let you know once I get back there. I figured it out when the fuel pressure in the rail dropped to zero when I shut of the engine almost immediately while trouble shooting the problem.

This, I didn't know!

Thanks.