HOW TO: Adjust trip computer MPG readings

[kpatz]

I figured I'd post this because I figured out the trick to adjusting the trip computer to (reasonably) accurately reflect true fuel economy.

You'll need a VAG-COM to do this.

The first step is to calculate your average mileage (preferably) over several tankfuls of gas. To do this, start when you fill your tank. Fill it until the pump shuts off, then fill until it shuts off again (to prevent premature shut-offs). Reset your trip odometer. Also, reset the average MPG in bank 2 on the trip computer (by holding down the reset button on the stalk after selecting average MPG on bank 2). Next time you fill up, note the total miles from the trip odometer and the number of gallons it takes to fill the tank. Divide miles / gallons = MPG. Reset the trip odometer, but don't reset the trip computer. Repeat over 2-3 tankfuls of gas and get an average.

Once you have a good idea what your actual average MPG is, check the average MPG in bank 2 of the trip computer. Chances are, the trip computer will be off some. Turn on the ignition (engine doesn' t have to be running). Hook up your VAG-COM, connect to the instrument cluster, and go to Adaptation channel 3. The default value is 100, and is adjustable from 85 to 115 (on my '02, I have to adjust in increments of 5, so 85, 90, 95, 100, 105, 110, and 115 are allowed values). If the trip computer's MPG is higher than your actual, adjust the value upward. If it is lower, adjust the value downward. Here's the cool part: When you save the adaptation value, the MPG figure on the display adjusts immediately. This makes it easy to find the correct adaptation value to get your trip computer on track. Once you get it as close as possible to your actual calculated MPG, exit VAG-COM, and you're done!

[DELUX]

I've been meaning to do this, maybe I'll do it today.

What setting did you use for your +1 setup?

[IronAudi]

i am amazed by how much shit you can do with this VAG com

[mnkyA4]

I just started this process and going to use Chevron gas. hopefully mine won't be that much off, haha

[wolfdog]

Nice! I don't think mine is too far off but I've never checked it really. I'll do so with this tank!

[old guy]

with the GIAC FX mine was off by 30%. The best I could do is to adjust it to 115% and still be showing 15% better mileage on the display than my actual mileage.

[cjonesgo]

Thank you! I had started a thread a few weeks back on how mine was not accurate. I was able to get some good info about this adjustment being possible, but this a great straight forward write up. good job!

[kpatz]

I've been meaning to do this, maybe I'll do it today.

What setting did you use for your +1 setup?

IIRC, I have mine set to 90 or 95, I forget which. For some odd reason (maybe my ongoing lean issue), my MPG readings were lower than actual after getting chipped. Afterward, they're almost spot on.

[doublezero30]

I figured I'd post this because I figured out the trick to adjusting the trip computer to (reasonably) accurately reflect true fuel economy.

You'll need a VAG-COM to do this.

The first step is to calculate your average mileage (preferably) over several tankfuls of gas. To do this, start when you fill your tank. Fill it until the pump shuts off, then fill until it shuts off again (to prevent premature shut-offs). Reset your trip odometer. Also, reset the average MPG in bank 2 on the trip computer (by holding down the reset button on the stalk after selecting average MPG on bank 2). Next time you fill up, note the total miles from the trip odometer and the number of gallons it takes to fill the tank. Divide miles / gallons = MPG. Reset the trip odometer, but don't reset the trip computer. Repeat over 2-3 tankfuls of gas and get an average.

Once you have a good idea what your actual average MPG is, check the average MPG in bank 2 of the trip computer. Chances are, the trip computer will be off some. Turn on the ignition (engine doesn' t have to be running). Hook up your VAG-COM, connect to the instrument cluster, and go to Adaptation channel 3. The default value is 100, and is adjustable from 85 to 115 (on my '02, I have to adjust in increments of 5, so 85, 90, 95, 100, 105, 110, and 115 are allowed values). If the trip computer's MPG is higher than your actual, adjust the value upward. If it is lower, adjust the value downward. Here's the cool part: When you save the adaptation value, the MPG figure on the display adjusts immediately. This makes it easy to find the correct adaptation value to get your trip computer on track. Once you get it as close as possible to your actual calculated MPG, exit VAG-COM, and you're done!

i only have one problm with this post, and thats the part i underlined. there is a check valve in your tank that is how the pump knows to shut off. if you keep filling it up AFTER it already shuts off, there is a chance that you will overflow your charcoal canister of your evap system with gasoline. and that is not good. cause they are not cheap. i dont know about audis...but my old nissan was in the $300-400 range. and thats a nissan, not audi. so ide advise you not to do that. otherwise, happy vaging ppl!

[cjonesgo]

this is not entirely true. While I do not disagree that there is a canister, and it is expensive... gas pumps themselves have a safety cutoff that is triggered with pressure. I do not know exactly how it works and am not trying to say you are wrong, because you are not. all I am saying is that the pump itself shuts off independent of what the car is doing by sensing air pressure in the tank.
even getting the damn things to work with motorcycles and most old cars is a pain!

also as a side note, there is a sticker on all gas pumps that says it is unlawful to "top-off" the tank by going past the pump cutoff. in california anyway.

[kpatz]

I've been doing it for years that way, haven't killed any charcoal canisters yet. Pumps shut off too early more often than not, the tank will usually take another 1/3-1/2 gallon, and by the second click (I never fill beyond that) it's full. Either that or after it clicks off, I'll pump up to the next whole dollar, or 50 cents, whatever's closest (with today's prices, that isn't much more gas).

[cjonesgo]

One great suggestion that came up in the thread I had going is to fill up the same way every time (to the stop, one past etc), and if you have the chance, use the same pump every time. just one way to further limit variables. In theory it wil help to provide a more accurate average in the long run.

[doublezero30]

this is not entirely true. While I do not disagree that there is a canister, and it is expensive... gas pumps themselves have a safety cutoff that is triggered with pressure. I do not know exactly how it works and am not trying to say you are wrong, because you are not. all I am saying is that the pump itself shuts off independent of what the car is doing by sensing air pressure in the tank.
even getting the damn things to work with motorcycles and most old cars is a pain!

also as a side note, there is a sticker on all gas pumps that says it is unlawful to "top-off" the tank by going past the pump cutoff. in california anyway.

im not 100% positive on how the pump knows when to shut off, but i believe the check valve (its just a little ball type deal) seals up once the tank is full (cause the ball floats and plugs the valve). the pump somehow senses this, and shuts off. but you can still 'top it off'. and i know for a FACT that this can cause the charcoal canister to fill because if you top off too much, the filler neck fills with gas, which will then in turn fill up the charcoal canister and ruin it.

[cjonesgo]

Yes, you can top-off until the thing is overflowing. That is not in debate. I was just saying that the pump will sense pressure in the tank and will cut off long before it will be an issue of overfilling. That is what it is designed to do.
I think that people go one click past etc. as a way to check that the pump is putting in as close to full as possible to limit variation. On hot days, I have had pumps cut off after putting in about eight gallons. I think it is smart to double check it as there are variables that will change how a pump will behave.

[doublezero30]

i wasnt argueing about over flowing from topping off, i was just trying to warn people that if u top off too much, there is a chance that you could be buying a new charcoal canister. thats all. you may like to double check and top off, but for me, i personally dont want to take that possible risk. now..../end discussion

[bbaudi382]

i agree with the guy with giac fx. once i got my injectors in, i was off by about 30%. fixed it to 115, but my readings are still off by about 15%. i calculated this by calculating actual miles driven vs gallons filled in at the pump over about 10 fillups...seems to be pretty consistently 15% too high still.

[stacks]

Fuck the canister, I'd be worried about my car catching fire.

[Gberg888]

Thanks guys! This is great!

[Mattkrim]

Thanks for the write up. I hate when it says I'm getting 5 mpg then shoots up to 130 when I ease off the peddle.