Ugh 12.6mpg

[Diesel JD]

Hey guys, I'm just wondering if you all think this is par for the course or if I should be doing better. Its on an '86 F250 longbed extended cab, C6 2WD 3.55 gears, 90% city 10% highway. I think my timing may be retarded...the truck is almost as quiet as a gasser sometimes after a long pull, I know I have some fuel return leaks, and an injection shop guy said it wash psuhing some fuel out of teh advance piston or weep hole, however I don't know how he could tell where the fuel was coming from given the amount of return line seepage Where is the weep hole and how is the best way to check for a leak there? Well just wanted to put it out there and see what you all think. Is this normal or not quite good enough? Also this is on B100 biodiesel, no or light load most of the time, good fuel additive almost always. Thanks,
J.D.

 

[icanfixall]

My thoughts are you really can't state the fuel mileage when you aren't burning it but leaking it out. Thats just not fair to your motor. I would fix the leaks then look at how many miles are on the injectors and pump if your mileage is still low.

 

[Diesel JD]

Gary I do agree with you...how is the best way to observe if the pump itself is leaking out the weep hole?

 

[The Warden]

If you see fuel in the valley pan, it's coming out either from the pump or from a line going to the pump. If it's a line, the line itself will be wet from the leak point down...so, if everything's dry except for the valley pan, it's definitely the pump. I don't think a return line leak would lead to fuel in the valley pan (unless it was ridiculously bad), but I could be mistaken...certainly, I would replace the return lines before going any further.

BTW, my old E-350 van had the same drivetrain as your truck, with 31x10.25R16.5 tires, and averaged 14 to 15 mpg. The previous owner told me that he saw 17 regularly before swapping rims and tires. So, I think your numbers are definitely low...heck, I was seeing 12 to 14 when I had 33's on my truck!! (with the T-19, 4.10 gears, and the turbo)

 

[Cheaper Jeeper]

My DD NA truck is almost identical to yours. 86 F250, 2WD, NA 6.9, C6, 3.55 SuperCab longbed. Only mods are a custom Y-pipe (2.25" at mainfold to 2.5" to Y to 3"), 3" exhaust with freeflow muffler, K&N Filter, dual ram-air intake setup, and the pump turned up 1 flat. Daily commute is 40 miles round trip - 25% surface streets, 75% freeway - though the freeway driving is almost as stop & go as the city streets and averages less than 40 mph (Seattle traffic sux).

Anyway, if I'm having fun with the skinny pedal I get around 14.5 mpg. If I'm making an effort to drive it easy and save fuel I get as high as 16.5 mpg. Heck I just got back from a 2300 mile round trip hauling a very heavy camper and towing a built up Jeep Cherokee up and down the mountains from Seattle to Moab Utah, and I averaged 10.3 mpg hauling 6000-6500 extra pounds.

If you're only getting 12.6 running unloaded and 90% highway, either something is significantly wrong or you have one heck of a heavy foot.....

 

[Agnem]

You could pick up a mile or two with good timing and no leaks.