fuel

Not necessarily very accurate, better double check it with miles divided by gallons used.

 

the computer only takes into effect drive fuel. and i beleive it does that by calculations relating to the throttle position sensor. but i could be wrong.

it can't account for idled fuel.

 

and how do you do that?...only way I know is to keep a full tank? it's not practical to do that on every load....imho

 

Check it a couple times to see how close it is. If it's close, great, if not, oh well.

 

accurate when injectors are new and trim code are entered

 

the problem is the idle time. you'll never know your mpg if there's idle time during any tank full.

doesn't matter if your using engine or apu. OR, in cab heater. your using fuel either way. my last truck had an espar bunk furnace.

i know my truck uses 1.1 gallons every hour of idle. so when i fill up. i take hour many hours were idled during the last tank. times that by 1.1 gallons. subtracted that from gallons added. and divided that number by miles driven.

example.

100 miles driven. 30 gallons to fill up. 5 hours idled.
5 X 1.1 = 5.5 gallons used for idle. 5.5 - 30 = 24.5 gallons used for driving.

100 divided by 24.5 = 4.08 mpg.

if you disregarded the idle time then you'd have 100 miles divide by 30 gallons = 3.33 mpg.

keep track of miles driven. and hours idled. and you can use the calculator on your phone to figure the real math.

my computer always gives me a higher number then the actuallity.

the problem, is figuring out how many gallons gets used for heating purposes when the truck isn't moving.