Tuning box and MPG question

[DeeJayB]

Hi All
So I fitted a tuning box to my 147 JTD, and was pleased to feel better response and power (although I've set it on 7/10 just because it feels nicer). I also seemed to get better mpg too. According to the computer I did 215m at 60mph average, and got 58.2mpg (if memory serves).
I included this in another post, and someone suggested that because the box sits between the ECU and the injectors that the mpg would be inaccurate- the fuel added doesn't match with what the ECU thinks happened.

So my question is this: does the computer monitor actual fuel consuption or what the ECU thinks it's used? My gut feeling is the actual consuption, but I really don't know as I'm still learning about this stuff.

Thanks

[JON156VELOCE]

They Measure actual consumption but are quite optimistic..
Is your car an 8 or 16 valve.? I removed the cat and blanked off the egr valve in my 8 valve 115bhp 156 and it made quite a differance to the power and fuel consumption

[DeeJayB]

Thanks for that - I thought that ought to be the case
Mines the 8V version. It's going in tomorrow to get a new aerial fitted (too long driving my last car that didn't need the aerial removing for a car wash... oops), so will ask about removing the cat. I'll do some reading about the EGR thingy too

[TribesMan]

Fitting a tuning box will make your board computer (more) inaccurate...

Board computer measures what ECU thinks it is consuming, not the consumption...

[JON156VELOCE]

Originally Posted by DeeJayB

Thanks for that - I thought that ought to be the case
Mines the 8V version. It's going in tomorrow to get a new aerial fitted (too long driving my last car that didn't need the aerial removing for a car wash... oops), so will ask about removing the cat. I'll do some reading about the EGR thingy too

Its well worth doing, the egr does nothing for power and economy,you can get a ready made blank on ebay for about £3 and its really easy to fit it wont cause your engine light to come on or effect the mot, neither will removing the cat.

I removed mine by buying a second hand cat and removing the middle of it, you can get a proper pipe to replace it but they are about £100, used cat was about half that plus about half an hour to remove the middle.

I still have the cat I took off if you are interested in de cating yours