As most of you probably know, my car is now equipped with a bigger than standard fuel pump (whalbo 400hp unit), bigger than standard fuel injectors (bosch 440cc units) and a non standard, rising rate fuel pressure regulator (among other things lol)

I'm wondering if the "Avg fuel consumption" calculation in the trip computer would be accurate? As at last night it was showing my average fuel consumption at 10.3L/100km. Admittedly that is only averaged over about 150km driven since the car came off the dyno, but I haven't exactly been going easy on it the whole time, and it now spends alot more time idling before / after being driven.

Does anyone know how the calculation works?? If it relies on set parameters which assume the OEM pump/injectors/fuel pressure are being used, then I'm assuming it'll never be accurate again, and I'll have to go back to the old fashion way of working out fuel consumption.

Not sure man, but I doubt 10.3L/100 is accurate. Maybe give it some time to adjust, or like you said, first time you fill up take note of litres put in and kilometers travelled and work it out that way.

In the Ford it calculates current fuel used (live reading) by amount of fuel in tank by amount of kilometers already travelled.. EG if i reset the ECU at full tank of fuel I have 450km in the tank. After I give my car a bit of stick it will adjust it to my driving style and read about 370km till empty.

I guess (if the ECU is smart enough) it would be the same for the Magna.


Although i must say, i never trusted the distance till empty in my TJ..

Fill your car up to almost overflowing (so you get the max amount of fuel in your tank 72L), reset the ODO and drive around till the fuel guage reads almost empty - note your DTE and AFC on the trip computer.

Fill up the car and note how many litres went in. Divide km's travelled by litres used.. VOILA! average fuel consumption. Then check this against your distance till empty and average fuel consumption on the trip computer which you recorded before and you will know if its accurate.

Yeah - I've never trusted the dist. til empty thing anyway, and I rarely let the tank go below 1/3rd full so that doesn't worry me. The only function I pay any attention to is the Average L/100km.

I filled the car right up last night, and I reset the trip computer, so next time I fill up I'll take note of the fuel I put in and work out the consumption based on the km driven up to that point.

Yeah - I've never trusted the dist. til empty thing anyway, and I rarely let the tank go below 1/3rd full so that doesn't worry me. The only function I pay any attention to is the Average L/100km.

I filled the car right up last night, and I reset the trip computer, so next time I fill up I'll take note of the fuel I put in and work out the consumption based on the km driven up to that point.

Mike,

I remember reading in the workshop manual that the trip computer sources it fuel consumption data from injector number 2 (or something like that) and then assumes all the others are doing the same until a different reading is measured. I assume then it uses some voltage based scale to determine how much fuel it believes it is delivering. So if you've changed your injectors it's possible that the fuel consumption is not as accurate as before...

Mike,

I remember reading in the workshop manual that the trip computer sources it fuel consumption data from injector number 2 (or something like that) and then assumes all the others are doing the same until a different reading is measured. I assume then it uses some voltage based scale to determine how much fuel it believes it is delivering. So if you've changed your injectors it's possible that the fuel consumption is not as accurate as before...

Thanks for the info Mark!!

I'll run around for atleast 300km and then fill the car to the max again and work out the fuel consumption that way - then compare it to what the trip computer is telling me after the same distance and see how close we get. Based on what you've said it sounds like the trip computer calculation will now be way out.

Thanks to the Greddy - the standard ECU has no idea anything has changed, apparently the emanage has a feature whereby you program in the capacity of the new injectors and (I assume) it automatically updates the fuel maps based on this (which can then be tweaked manually).

When I got my stage 1 cams and whatnot installed, back when I still had a piggy back ECU, I found that my average fuel consumption, along with my fuel usage counter in the trip computer were wildly inaccurate - to the point that the trip computer would tell me I had only used 52L but I'd fill up to the tune of 60L and my fuel consumption was telling me, like you, that I was closer to 10.5L/100km when before the mods (when I had less power) it was more like 12.5L/100km.

Since I've had my E6X in there, it's gone back to being accurate.

Its a far stretch to say that they are accurate even when stock.

They assume too many things to be accurate when modded. They assume things like fuel pressure, standard injectors, wheel size, diff ratios, wheel width, aswell as more. If those things change even slightly they will effect the accuracy quite a lot.

When you reset the ECU and have to choose between sedan and wagon, that's only to do with the amount of fuel in the tank, wouldn't be used in the fuel consumption calculations right? It'd seem logical to work out the fuel consumption from the amount of fuel in the tank/ks travelled.

and I rarely let the tank go below 1/3rd full so that doesn't worry me.

u should run your tanktill almost empty some times mate, gets rid of the crap at the bottom of the tank, topping up all the time when your at 1/3 will only let the nasty's build up.