afaleti

I just noticed that the Mode that displays the current fuel consumption in my 99 LS400 is faulty, it shows Readings as High as 5mpg down to 49mpg ( I wish).

Does anyone have the slightest clue as to what needs to be replaced and what it might cost?

All the other modes work perfectly.

Range
Elapsed Time
Average gas Consumption
Since last Refill
etc .....

flkey

'03 LS430 COCOON
"Current" = instantaneous mpg, if one coasts, the '03 goes to 99.9, at full acceleration to 0.
Go to tank average for overall mpg. I find this feature to be quite accurate when calculated
by hand ie., miles divided by gallons equal miles/gal.
Hope this helps.

viskha

As stated above, your readings seem to be very plausible and accurate.

buttons

these things are almost like the old vacuum gage 'milage meters'; let up on it and it goes higher, mash the gas pedal down and the gage goes lower. SIMPLE.

That is all it is trying to do to make you get better milage. But is instanteously correct:
mi/gal= miles/hr divided by gal/hr !!!!

flkey

buttons
your math is correct, but we have no gal/hr measurement. Lexus engine management system must measure flow rate [as you suggest], but then it is converted for you as displayed in mi/gal = mpg.
I have 10300mis on my '03 LS430, the mileage display shows I'v gotten 21.0 mpg since new, I'm delighted.
Have gotten as much as 29mpg, about 100mis at 55mph on the flatlands of FL.

Maltrix

Necroing this thread to be polite and not start a new one.

I recently purchased an 1999 LS and my current mpg is all over the place, 7, 22, 99, 30, 18 etc etc. According to this thread thats normal and the computer just giving instant reads as it finds them? I dont believe that to be case though and was wondering if anyone could confirm?

sha4000

iTrader: (1)

You have to scroll through the info display to get to the correct mpg. The one your in always fluctuates like that.

python

iTrader: (4)

why people are so worried about what that stupid meter says is baffling. fill up...drive it...fill up again. divide mileage by gallons. mpg figured! if u get 24 or 25 or 22 who cares? its not a commute car...if ur using it as such u might wanna rethink ur thinking

Banshee365

if you havn't gotten your answer with the replies above, I will sum it up for you. What you are explaining is completely normal and how it is designed. You may be looking at it like an average mpg. But current mpg is what the car is consuming at that very second. You will see single digits on harder acceleration off a light and you will see very high numbers when coasting or decelerating.

Stroock639

yea the "current" mpg display will go anywhere from 0 to 99.9 mpg. if 49 is the highest you've seen then you've never gone above 20 mph lol... go to the display that says "average" hold reset and it'll tell you more workable numbers

hsitko

I believe that this system exclusively uses your oxygen sensors to determine fuel mileage. No one else knew this? Interesting...I have been a mechanic for a lot of years now. Most of the oem's use the oxygen sensor to determine mileage. And to answer your question those readings are not always accurate. If you let off the gas they go waaay up. But by and large they are accurate for tank average at least.

dicer

O2 sensors would not be an accurate measure of fuel economy. Why? Because they strive for close to perfect mixture at all rpms and load conditions except of course WOT. Measuring the fuel ratio means nothing for a MPG measurement. Why? To use just that there is no way to know if you are measuring a 1 cylinder lawn mower engine or a 28 cylinder aircraft engine. Fuel ratio is just a relationship of air to fuel and if said sensor was plugged into either engine I mentioned its just gona measure what I said it would. So since the injectors are known size metering devices and it can be calculated what they flow against their on and off times, it makes more sense that the pulse width and frequency they are on and off is how the mileage is calculated.

Banshee365

I would imagine that a factor of speed vs engine load against an engineered logirythm predicts fuel consumption. Engine load is measured in nearly every modern car so it seems to me that tapping in to that info against your speed plus a logirythm would be able to closely predict fuel economy. The injector pulse width may play a factor in engine load calculation as well.

sam12345

iTrader: (1)

By the way it is accurate when you let off the gas to get very high mileage since under certain conditions the fuel is completely cut off. 99 is the upper limit of the gauge but you are using no fuel during these instances. Example coasting in gear down a hill and engine is above a certain rpm. Letting of the gas at highway speeds ect..

sam12345

iTrader: (1)

From another forum
.contemporary cars that I've had detailed info on. The typical method for port injection engines is for the trip computer to keep track of the fuel injector on-time or "duty cycle". On a port injected engine the fuel rail pressure is kept very constant, so the "on time" of the injectors is a very accurate measure of the total fuel used when integrated over time.