Typically I get 15mpg empty but on my last 500 mile trip pulling my TT ( about 8000 lbs ) i got right at 9 miles to the gallon . Seems like a pretty big drop off . It was almost all interstate and at 65-70 miles per hour . This was from Atlanta to Orlando so not alot of climbing .
IC boots look fine with no problems but i do notice about a 3/4 inch wide strip of suit around the drivers side up pipe . Passenger looks ok . Would this leak be enough to cause a sharp drop in mileage or should I look elsewhere ?
I am a bit disapointed with the power I have while towing but its completely stock except for intake mod and Im told the Ford PS is kind of a dog without a chip .

early 99 F350 CC 4x4

 

early 99....Thats your problem..

 

Do you have gauges?? Boost, EGT, etc

 

that leak doesn't help..get it fixed... also check you IC and spider pipe boots ..your EBPS tube is most likely pluged as well.

 

And the answer is yes. Any uppipe leak will prevent you from making all the boost you can and should under a load. Fix that leak and your unloaded mpgs ought to go up some too along with performance.

 

and hes I have guages, egt boost and trans temp

 

I was refering to the op..I know you got PMS Stroken. To give us a baseline boost and egt readings. I concur with everyone in regard to the up pipe leaks. IH has new pipes out, cost about 325 bucks. The new design does away with the traditional do-nut type seal that are extremely unreliable. I have the pipes for my own truck, haven't had a day off to put them on.

 

Thanks for all the quick replies . No I dont have gauges . I should at least throw in a boost gauge since it would help me troubleshoot this problem.
Looks like an order for those bellowed up pipes are in my future . I just dont look forward to that knuckle busting work.
Just seems odd that most everyone else on the site that talks mileage doest suffer a 6 mpg drop towing lil ole 8k pounds .
I cleaned the tube about 3 months ago ( because of all the good advice on this site ) so it should be ok .

Scott

 

I have an early '99 and get 17-19 all the time, I believe his issues run deeper than that.