Mpg Gauge

[84Stoney]

I know that the real-time MPG gauges, such as the one on my (and, I assume, everyone elses!) IS200, can often be inacurate. But I was wandering how it actually works, and does it take into account any modifications (like my supercharger!)?

I have discussed this with mates and nobody really knows, I would be interested to find out.

I calculated myself that i am averaging around 16-18mpg! That may be due, in part, to my driving style! I'll get over the novely of the charger one day, and ease off a bit, I'm sure!

[KevLex]

Looking at the schematic for the economy gauge it would appear that it takes signals from the engine management, the ABS controller and the speedo sender. There is some control electronics inside the dash unit which evaluates the fuel injected quantity information (from the engine management ECU) and the distance information (from the speedo sender) and produces an instantaneous fuel consumption indication.

This system will take into account engine modifications as it measures the amount of fuel being injected into the engine. The distance travelled information will only be accurate if the rolling circumference of the tyres is correct, i.e. correct inflation, wheel size etc.

I always find instantaneous economy indicators quite useless and distracting, particularly on a vehicle that is not noted for its frugal performance!

Occasional calculation of trip economy from tank-to-tank fill up is a useful indicator that all is well with the car.

[durg]

The ECU knows a lot about what's going on with the engine and the car as it's running. It calculates how much fuel to put into the engine all the time using a map (data table) that has input figures such at throttle position, engine water temperature, outside temperature... It therefore can calculate mpg from these figures. I've noticed some other comments previously about mpg while stationary - in most systems (and this is the case with the Lexus one) the system does not operate until you are going above about 10-15 mph. The reading of 0 mpg when idling is there because the system is not operating and not for any other reason - however it is right that you are doing 0mpg when stationary. Overall the systems are reliable because the value is generated from real data by the car - it knows how much petrol is being squirted in! If you have the car re-mapped properly then it should still give a decent reading. Old style systems used the induction vacuum to calculate mpg and these were less reliable. The gauges had to be calibrated for each specific vehicle. Hope this helps and correct me if I'm wrong anyone :)

[The_Stig]

The only thing mine seems to measure is pressure on the throttle!

[VVProtocolVV]

Personally i wouldn't miss the mpg gauge on my IS if it's taken away. At least on the Civic theres just a green "ECO" that just lights up to let you know when you have reached the optium mpg (which is around 60mph in 5th gear).

[boddamloon]

I never really take notice of it. I think if you are sitting at around the 60 mark and no heavy accelarating you will get the best out of your fuel. The MPG guage is just a bit of a gimmick its a bit like a chronograph watch IMO

[84Stoney]

I totally forgot i stated this thread! just found it again.

Thanks guys, that pretty much what i wanted to know!

Calculating manaully i find i get 25mpg, cruising at 100mph in 6th. Which is not bad IMO.

If you cruise at speady spped, i wander if the mpg meter will show a visable difference with SNOW mode on?

[DJ Wozza]

If you cruise at speady spped, I wonder if the mpg meter will show a visable difference with SNOW mode on?

erm why don't you try it

[84Stoney]

If you cruise at speady spped, I wonder if the mpg meter will show a visable difference with SNOW mode on?

erm why don't you try it

OK then, I will.