Been trying to figure out why I was getting bad mileage (14 1/2 to 15) on the 92 5.0 with the auto tranny. Also had a little shudder at 30 and 50 mph.

New fuel filter.
New trans fluid and filter.
New IACV to stop stalling when letting off gas too quick at low speeds.
New PCV valve.
New rotor, cap, plugs, wires.
No codes.

Still not great, only getting 15 to 15 1/2 mpg.

Went out today to check transmission fluid, noticed number 4 spark plug wire loose. Guess I didn't get it on tight leaning over the fender.

Hoping this solves my problems. Sure seemed to have more power when I drove it. Didn't have that "ugghhhh" feeling getting to 65-70 mph.

 

15 is not considered bad for that truck.

 

I've owned it since new, used to get 18 routinely. Back in the days of 55mph limits would bump 20.

It's more worn now, but I'm thinking it ought to do better than it is.

Edit: Still got a little transmission issue, but going to try one of the additives the guys here recommend before pulling it.

 

you did drain the convertor i hope.

what brand/kind of plugs, wires and cap?

 

Check those stupid plastic vacumme lines too. I found so many of them. I just bought a roll of vacumme hose and went to town replaceing them all.

 

Yep, drained the convertor thanks to the advice here.

Went with Motorcraft on everything except the tranny filter. Hadn't started on the OEM kick at that point.

 

Next on the list. Also thinking of the canisters. Not hearing any leaks though, can you hear them with just your ear?

 

you can spray all the vac lines with wd-40 if its leaking the idle on the truck will change

 

My truck gets 15-16 city/highway mix mpg so I wouldn't say yours is getting bad mileage. It has gotten 17 before. I try to keep mine maintained and serviced as much as I can. It runs great. I don't think it well ever get any better milages than it does now.

 

I'm getting 17.5-18.5mpg currently. It dropped when the ethanol was added to the gas for up to 10%. It would do 19-19.5mpg when new on unleaded without any of the corn syrup. That is easily part of your mpg issue.

 

Jonas, What motor tranny rear gears and tire size do you have?

 

18-20mpg's?? WOW.

oh oh, I feel another mpg thread coming on.

I've owned my 93 since new. It has never gotten more than 16mpg.
Mine is a 302, E4OD, 3.55 gears (when new) 265-75R15

I never put any thought into the ethanol effecting milage.
Might explain why I can't get over 12 mpg's now. About 2 mpg less than after when I originally regeared. Immediately after regearing with 4.56 gears & 33's it would deliver 14 mpg's tops.

 

Ethanol, propane, natural gas, produces less power when burned than gasoline, so it's almost logical why you'd need quite a bit more fuel if these substances are mixed with gasoline either in the fuel itself or after the fact on the vehicle (carb mixer).

As the vehicle ages, you have more and more blow-by and this reduces MPG as well as some of the pressure from the controlled explosions are lost past the rings.

Cat's clog up increasing back pressure thus reducing any potential for cylinder scavaging. Dying sensors and rotted wiring impact the EFI computer's perception of what is going on. Old dirty oil increases friction in the engine, same for tranny fluid and rear axle oil.

Gearing and tire diameter impact this as well, as does lifting the truck to the sky.

The biggest factor is driving style... Unless I'm towing, uphill or merging, I shift my F350 crewcab into overdrive by 35 miles per hour or so. Why? Keeping the RPMs down keeps the 5.8L from drinking. It's torquey enough at the lower RPM range that this is fine except for towing, going uphill, or trying to merge on the highway. I can easily keep the truck in single digits MPG by shifting aggressively and using some of the RPM range that's available, but unloaded there's no need for that especially on the local streets around here.

Also keep in mind a truck is essentially a land yacht. They're not aerodynamic nor are they light.

How many of you have 500lbs of bedbox and tools out back? Junk in the bed? 500lbs of push bars, custom bumpers, caps, spare gas cans or oversized gas tanks(gasoline weighs about 5lbs per gallon)? Bigger tires and wheels are heavier. Wider tires have a greater contact patch therefore gives more rolling resistance so you have more resistance to movement - i.e. requiring more power to turn than stock tires. There's a reason why the original tires aren't massive in diameter or very wide, and this is it.

Just some of the reasons why mpg goes down... trucks are designed to haul stuff, and that's why most of the components that make up the truck are large and heavy, stout and strong, and of simple design - it's less likely to break when hauling stuff.

 

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