141.9 mpg in a GTA!

Driving back from my parents over Christmas and with out even trying, noticed the trip computer was showing 141.9 mpg for a good minute or two! This was driving down a gradual hill for about a mile and a half at about 45ish in 6th gear. I have seen it in the mid 80mpg’s a few times when I have stuck it in neutral down hills but this took me by surprise some what! Wish there had been someone else in the car now to snap a picy of it! It also pushed my average consumption up to 37 mpg over a 275 mile trip. Anyone else had bonkers mpg readings with out trying?

kind of defeats the point of buying a GTA IMHO...

Originally Posted by Chris155

kind of defeats the point of buying a GTA IMHO...

No need to be like that.

meh

Like i said i was not trying!
Though I am a bit Embarrassed of it tbh so have been giving it a good thrashing since then and its now back down to regularly sub 20s again!

Originally Posted by Knightboat

Driving back from my parents over Christmas and with out even trying, noticed the trip computer was showing 141.9 mpg for a good minute or two! This was driving down a gradual hill for about a mile and a half at about 45ish in 6th gear. I have seen it in the mid 80mpg’s a few times when I have stuck it in neutral down hills but this took me by surprise some what! Wish there had been someone else in the car now to snap a picy of it! It also pushed my average consumption up to 37 mpg over a 275 mile trip. Anyone else had bonkers mpg readings with out trying?

Not too shabby dude, must be up for some kind of Alfa record!

I've actually got a pic of my display showing exactly the same mpg - 141.9

I'd say it's possibly complete horse sh*t to be honest? Some sort of default value?

Originally Posted by double-6s

I've actually got a pic of my display showing exactly the same mpg - 141.9

I'd say it's possibly complete horse sh*t to be honest? Some sort of default value?

So I was not going mad then! Agree with it probably being some sort of default value as can’t quite believe the car could do that sort of mpg even if you were really trying to.

With a modern car, when the cars momentum is driving teh engine along rather than the other way around (eg going down hill with no accalerator) no petrol is injected into the engine at all, so in fact, for that moment, the fuel economy is infinite. But since the GTA readout seems to be a regular update rather than an instantaneous readout, I'd guess it takes the average over 30 seconds or so (would have to time how often the display changes to be sure)

As for defeating the point of buying a GTA - eh?
Noticing a high readout at one point while driving along? Think that post might be a bit of an over reaction Chris.

Originally Posted by bazza

As for defeating the point of buying a GTA - eh?
Noticing a high readout at one point while driving along? Think that post might be a bit of an over reaction Chris.

meh.

my brother's at it too...

Alfa Romeo forum: who said that GTA’s were uneconomical?

Surely petrol is injected into the engine at ALL times? or how does the engine fire? What's burning if it's not fuel? because the thing is still igniting at least 1000 times per minute?

Isn't it?

Originally Posted by Knightboat

Anyone else had bonkers mpg readings with out trying?

Never got above 141.9, it must be the limit for whatever alogrithm calculated fuel economy.

I did manage to get that magic figure at 80mph in neutral though

Originally Posted by double-6s

Surely petrol is injected into the engine at ALL times? or how does the engine fire? What's burning if it's not fuel? because the thing is still igniting at least 1000 times per minute?

Isn't it?

nope, when you 'back off' the fuel is cut until it drops below around 1500revs to save fuel. it is actually more economical to NOT dip the clutch when going downhill as the car needs fuel to tickover but with you foot aff the throttle going downhill you aren't using a drop, hence the high reading

Yeah so is that not instantaneous though? Prolonged periods of cruising at tick-over surely requires fuel?

Sorry, struggling to get my head round it

as soon as you touch the pedal again the movement is picked up by the pedal position sensor and fuel supplied again so if you are tootling around at 1500revs constant speed (foot off the clutch) then of course you will use fuel, it's just when you are going downhill you your feet off all pedals the fuel is cut off altogether (no fuel is needed in that state so why deliver it?) , the changeover to fuel back on again happens so quickly you would never know it has happened, and also as there is no fuel for the plugs to burn you actually will get better engine braking

But how can there be no fuel for the plugs to burn? How is the engine turning over 1000 times a minute when you're free-wheeling down hill?

the engine is being forced to turn over by the weight of the car forcing it, as you go down a steep hill and dip the clutch you will gain speed, if you take your foot off the clutch (still in gear) the engine acts as a brake and is forced to turn over at whatever engine speed relates to the speed your car is going. if you switched the ignition off (please don't try it as it's too easy to turn the key too far and put the steering lock on ) the engine would still rotate at the same speed as it is being forced into doing so by the mechanical connection between the road, your wheels, driveshafts, gearbox, flywheel to your engine. that cannot change unless you change it by dipping the clutch. hope this is making sense . manufacturers use this to keep emissions down and create the good fuel figures we cannot reach

if by 'free-wheeling' downhill you mean with the clutch pedal pressed then you will of course need fuel for the car to be on tickover, which translates to the car actually using more fuel going downhill with the clutch pressed (car ticking over) than with your feet off all pedals

Cool. I understand now Mr Faulty

reference to the bit about turning the key off while going downhill to save fuel, a mate of my brothers tried that with the inevitable result that the steering lock came on and when he got to a bend near the bottom of the hill he suddenly found he couldn't steer and ended up in a field was a bit gullible though, he once was told all morning that he would have to check the anti-freeze on his battery. come dinner time he was out there with fresh anti-freeze to top it up he took some convincing to NOT fill it up apparently

Originally Posted by double-6s

But how can there be no fuel for the plugs to burn? How is the engine turning over 1000 times a minute when you're free-wheeling down hill?

If the engine is turning at around 2k or more with no input from the throttle the management shuts of the injectors completely.

Originally Posted by Chris155

If the engine is turning at around 2k or more with no input from the throttle the management shuts of the injectors completely.

On the 147 (GTA), you can display the instantaneous fuel consumption on the display... You can actually see when the fuel injection cuts out...
I have mine set to display kms/litre, when the fuel cuts out it jumps to 50 kms/litre, apparently the max it can display... You can also feel the engine braking more at that point....