You know, the one thing people never seem to consider in these discussions are the inaccuracies involved with checking MPGs.
My truck's speedo was off when it was bone stock and brand new! It turned out that 33 inch tall tires corrected it to dead nuts category. Before that, I thought it was getting great MPG because it was indicating more miles (and more mph) than actually driven. By correcting the actual miles driven, I was getting 1 mpg less than I thought I was. Bummer! The error could be the other way too depending on the particular situation.
The other thing is... how many of use sit there and dribble the fuel in to a consistent point every time? We know that diesel foams... and foams more in our trucks than it does in others (design of the filler). Some fuel brands seem to foam more than others too. The point is that it's tough to get the tank consistently filled to the same point every time. To do it requires 15-20 minutes at the pump. If your fill is a half-gallon off from the previous (easy to do, I have found), it throws the mpg off (e.g. 190 miles using 12.1 gal is 15.7 mpg vs 190 mi using 12.6 gal is under 15.1 mpg). I can get two full gallons into my rear tank after the pump shuts off (and foam boils out of the filler) if I dribble it in until it reaches the very top of the filler neck.
My thoughts are that many of the people bragging about great mileage or complaining about poor mileage are not accurately checking their mpg. No insult to anyone is intended, but I see few people **** enough to go as far as needed to be accurate... and I know how **** you have to be! ( : < )
To step up to accurate results, you have to start with an accurate odometer (or discover the correction factor to use with the math) and you need to fill the tank to the same point every time. Or, if you have the means, use some form of instrumentation to check mpg.
I run my truck over a few measured miles (with no turns) until I get a correction factor. If you go exactly 1 mile but your odo indicates only 0.9, a ten percent (0.10) difference, you take your miles at the end of a fuel run and multiply it by 10 percent (0.10) and add what you get to the total. If you went 1.1 miles, you are 10 percent over so you still multiply by 10 percent again, but subtract that result from the total miles.
And then we have all the modifications that can throw things off. If you have a tire size upgrade, or a gear change without replacing the speedo drive gear, it throws the odo off. Wide tires increase rolling resistance. Tall tires and lifts increase aero drag. More weight equals more work for the engine and less mpg. It goes on and on and doesn't include wear and tear from 20-30 year old trucks.
RE the Ford vs GM mpg (I've had both), remember you could get the GMs in a half-ton platform. Look at what a 6.9L does in a lightweight half ton! If you take two 8600# GVW trucks with similar configurations (e.g. 4x4, non overdrive), one a GM 6.2 and one 6.9L Ford, my experience is the Ford is often a little ahead mpg-wise because it makes more torque than the GM so doesn't have to be thrashed as hard in normal driving. Looking at some of my old magazines from the '80s seems to back that up. Something like 15-16 was about the best they got driving normally with a 3/4 ton HD... and that's from odos that were reading optimistically. If all were off like mine, they were getting 14-15 in true life.
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maybe next week if i have some time ill get to it that is if i dont get sent some where does anyone know of a good place to find the timing tools needed for these engines?
