Mileage - Why so different?

[R32WA]

Hi all.

My Dad and I both have Holden Commodore utes both the same year both 6 speed manual both have full exhaust systems on the only difference is Dads runs 3.7 diff gears and mine runs 3.9s yet his will do near 750km to 60L no matter how he drives, around town air con on or off and mine will struggle to get 450 to 60L if I baby it and dont go above 3k rpm and really try to baby it along. His already had the tune in when it was purchased. I have looked and looked and looked over both tunes to try find why his is so much better and the only 2 things I can see is the calculated tire size and spark tables thats different and I know his PPK in the instrument cluster is set up for 3.7s but then so is the ECU. I drove them both along the same route and they both show the same distance but could the cluster PPK and the ecu set for the same show a false reading? Im trying to squeeze as many km's to a tank as I can, I just bought a house and moneys going to get tight. Any ideas anyone?
Cheers

[Billf6531]

That's quite a variance. Are you getting your fuel mileage calculations from the vehicle display, or from filling up at the same pump at the same time of day and manually calculating fuel mileage?

[R32WA]

That's quite a variance. Are you getting your fuel mileage calculations from the vehicle display, or from filling up at the same pump at the same time of day and manually calculating fuel mileage?

Off the vehicle display, even is litre/100km is signifigantly different mine hovers around 13.0/100 to his 10.5/100. His fuel gauge even stays fuller for a lot longer vs kms travelled. Its got me stumped.

[Dust]

Babying it is not always the best way to get good gas mileage. A turtle launch at the stoplight will net you less than a determined start to get up to speed. The faster (within reason) you get up to speed, the better you are. Why don't you trying trading vehicles with your father to see if it is the vehicle or the driver?

[informationjunkie]

add up differences of driver style, car, traffic and you can get a wide variance.
try calculating you mileage manually and it might not be so different. if you are getting it from the display look and see what the average speed is of both, if it will tell you. if you sit at a stop more it will show up here.

Babying it is not always the best way to get good gas mileage. A turtle launch at the stoplight will net you less than a determined start to get up to speed. The faster (within reason) you get up to speed, the better you are. Why don't you trying trading vehicles with your father to see if it is the vehicle or the driver?

i noticed a good change when i stopped being so easy on the gas, so i don't baby it anymore.

[R32WA]

Average speed is about the same 50 to 55km/h, I know driver differences will give different results but 300 odd km?? I guess the next thing is to fill them both and run them on a trip and then fill them up again to see the difference. Still doesnt explain why the dash display shows so different though.

[SweetS10V8]

Still doesnt explain why the dash display shows so different though.

Its simply because they are terribly innacurate!! Ive manually calculated many vehicle that werent even close.

[Billf6531]

The dash differences are due to the differences in value programming in the two tunes. One is a custom operating system; differences in the R/L millivolt biasing for the O2s; differences in the lean cruise values; differences in the VE, etc. Please report back with actual, accurate mileage calculations from controlled fill-ups.

Average speed is about the same 50 to 55km/h, I know driver differences will give different results but 300 odd km?? I guess the next thing is to fill them both and run them on a trip and then fill them up again to see the difference. Still doesnt explain why the dash display shows so different though.

[R32WA]

The dash differences are due to the differences in value programming in the two tunes. One is a custom operating system; .

So which one is accurate then? If the custom OS is supposedly correct and the standard OS has the larger than stock values is it just lying to the driver by showing inflated figures? They both run the same size wheel/tire combo yet the tire calcs in the tune are different but the speedos read the same as verified by GPS.

[Billf6531]

You're still guessing. Post some real data, and a log from each vehicle, and we can analyze further. In my experience, dash displays are garbage, since who knows what elements they actually measure in order to calibrate fuel mileage.

[Dust]

Write down the distance and fuel used. I had a DIC that would read within .1mpg until I got a different PCM, then it was about 10% off.

[R32WA]

You're still guessing. Post some real data, and a log from each vehicle, and we can analyze further. In my experience, dash displays are garbage, since who knows what elements they actually measure in order to calibrate fuel mileage.

Anything in particular you would like to see logged?

[Billf6531]

Sure, if you do a search, there's a thread on creating a mileage pid that uses logged data. Log those elements from both vehicles in the table, and see how the mileage differs.

[R32WA]

Sure, if you do a search, there's a thread on creating a mileage pid that uses logged data. Log those elements from both vehicles in the table, and see how the mileage differs.

Cheers I'll have a search.