2nd Gen Non-Engine/Transmission All you gurus...Fuel mileage/computer?

[gatoram]

This may seem like a routine question to some, but I need help. First, I put some 315/75 BFG's on my truck which threw the odometer, speedometer, and fuel mileage computer off. Using a GPS, I calculate it to be reading close to 15% under(Florida Highway Patrol was kind enough to also point this out to me with blue lights flashing!). Running in fifth gear with the speedometer at 65 mph and the tach at 2000 rpm, the GPS says 75. 1 mph. The computer, at this speed, varies from 19 to 22 mpg. Total driving, town and highway, averages around 19. 4. Do I need to add 15% to the computers figures to get the actual mileage? I realize i could do the pencil and paper thing but enjoy watching the computer.

I would be satisfied with the 19. 4 mpg presently shown, but this enquiring mind just wants to know... ... ...



Thanks, Tom

 

[chuck3]

Mine read pretty close when stock, I double checked it with calculator. I added the EZ, got innaccurate, added DD1's was even more off. Allmost any thing you do will throw these off. Especially any thing that adds more fuel.

 

[HC]

Since you've got a gps, do this:

Step 1:Set Odometer trip meter and GPS trip meter to 0. 0 miles. Drive somewhere this is more than 10 miles away. The GPS miles are the "real" number. Figure your correction factor (CF) = odometer miles divided by gps miles. You should get a number like 1. 0543, 1. 0734, whatever. My point is that if you do it right the number is a little bigger than one.



Step 2: Now, drive at least three tanks of fuel. Note trip computer mileage, and calculate mileage the old way. Use indicated miles / gallons, then multiply this number by your CF to get true miles per gallon. On each tank, how much difference between "true" mpg and calculated mpg? After you've done this three or more times, average it. Probably will be 3. x or 4. x mpg with your mods.



Step 3: In the future, you can get pretty close by just subtracting this number from your trip computer mileage.

Clear as mud, right? (remember, you asked!)

 

[gatoram]

Thanks for the input, guys. HC, I'll try that and see how consistent the computer is.

 

[work2muchplay2little]

Here's a way to fix your speedometer/odometer by adjusting the input from the speed sensor. Mines still spot on with my GPS a year later. https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=22253