fuel computer accuracy

[05Limited]

Originally Posted by avalon01

really? doesn't even look at the fuel pump rate?

maybe I'll ask the prius guys, i know they have incredibly accurate fuel computers and they might know what toyota's putting in other vehicles.

with all these computer controlled cars there's no reason why the fuel computer can't be almost perfectly accurate, at least less than 5%. I mean the car knows how far it's traveling and should know how much gas it's squirting into the cylinders so what's the problem? At least the average mpg should be less than 5%.

I agree it could be done and that it should be done, but even that fancy NAV based computer thing that is in my car is not all that accurate. I'd rather rely on a very accurate gas guage and a calculator. But I'm getting really lazy so when the idiot light comes on, this idiot pulls into a nearby gas station.

[avalon01]

Originally Posted by 05Limited

I agree it could be done and that it should be done, but even that fancy NAV based computer thing that is in my car is not all that accurate. I'd rather rely on a very accurate gas guage and a calculator. But I'm getting really lazy so when the idiot light comes on, this idiot pulls into a nearby gas station.

NAV is completely different.

it's a new idea

it relies on things the car cant control (the earth, maps, roads, weather, etc etc etc)

trip computer is based entirely on everything inside the car, hell the car's damn computer has to keep track of all this stuff anyway to keep the car moving so all it has to do is display the number's it's reading.

not that hard really....

usually i'm lazy too, but with gas jumping 30% in a week I'm a bit pissed that my car isnt getting what the trip computer says it should be getting. Either the trip computer is waaaaay off or there is something very wrong with my car.

Oh, and it doesnt help that the TN forum is worthless when it comes to information of anything but camrys.

[foompla]

anyone who takes the trip computer to heart as anything more than a gimmick is sadly misinformed imho.

[johnd]

I can't talk with authority on the Avalon system, but I am familiar with some other cars.
They use what is called a flow meter. It senses the fuel that is flowing to the engine. This and in conjunction with the miles driven (sensed from the odometer) then computes a running total upgraded at intervals as to the miles covered and how much fuel that has flowed to the engine. I know this is the method used in my previous car, a 99 Volvo S-80. I also know it was used in some of the older cars because we use to get the flowmeters and use them in our home built aircraft. The Volvo upgraded the information every 12 seconds. My friends 89 Chrysler uses the same system.
His is very accurate. He has driven it down to 2 or 3 miles to empty (miles remaining) and then filled it up and the total put in was within a tenth or so of what the tank was published to hold.
The mpg in the Avalon may use this type of system, but the fuel range remaining doesn't seem to be adjusted for the computed mpg. Mine is more like it resets itself (automatically) at fill up and then just counts down the miles to go with what seems to be based on about 20 mpg. It adjust very little for the mpg readout.
The mpg changes a fair amount, more sensitive just after fill up. Just think of it as that first acceleration out of the service station is low gear etc, the mpg for that may be as low as 5 mpg and it last for say 15 seconds. then the next 15 sec is at cruise at 30 mpg. Those two averaged is (5 + 30= 35, /2) is17.5 . The more you drive at the 30 mpg, the less influence the initial 5 mpg has on the total.
Thats my 2 cents worth. I use the gage and fill it up when it gets low, then compute my mpg. Been doing that since 1946.