I'm back!

[Ninja]

Hi guys/gals.. Just thought I'd say hello after being off the forums for a few months due to house move etc.

Now, as not to waste this post.. I do have a question;

My MK2 golf is getting SUPER low MPG according to the MFA! Are these known to be faulty? I mean, I let my golf coast down a hill last night, and only managed to top out at 21MPG. So I put it into fifth, at 40mph and my MPG went down to 18, then 15... and If I floor it in second, 8MPG!!!!

I put £20 in the other day and managed to get around 150 miles out of it before 'needing' to fill up again.

[Ben Lessani]

1. Coasting is bad for fuel economy - leave it in gear
2. Putting it in a high gear is also bad for fuel economy - put it in the appropriate gear where the engine isn't labouring
3. 150 miles to £20 sounds alright
4. Dodgy MFA is usually dodgy MFA or blocked/leaking vacuum feed.

[Ninja]

1. Coasting is bad for fuel economy - leave it in gear
2. Putting it in a high gear is also bad for fuel economy - put it in the appropriate gear where the engine isn't labouring
3. 150 miles to £20 sounds alright
4. Dodgy MFA is usually dodgy MFA or blocked/leaking vacuum feed.

1. Never knew that - although it doubled my economy, lol.
2. I thought the lower the RPM, without engine labour was more economical.
3. I put twenty in last night just above the red line, im going to test it more accurately.
4. I hope it is a dodgy mfa and not something like my injectors.


Cheers for the reply

[rubjonny]

1. dont agree with this at all, letting a car coast at idle will use less petrol than leaving it in gear. However doing this isnt safe as you dont have proper control over the car. I certainly wouldn't coast down a hill!
2. yes this is correct, but as above dont let engine labour. otherwise why would VW have fitted an uber tall 5th to the carb models and labled it E for economy?

do the avg speed and distance travelled settings work properly?

[Ben Lessani]

1. dont agree with this at all, letting a car coast at idle will use less petrol than leaving it in gear. However doing this isnt safe as you dont have proper control over the car. I certainly wouldn't coast down a hill!

It depends on the injection system, modern injection (perhaps digi) are smart enough not to inject fuel when there's no throttle and let the wheels turn the engine over to prevent stalling. Stick it in neutral and then the engine has to supply fuel to prevent it from stalling.

[rubjonny]

hmm thats an interesting one, never heard of an injection system that can do that...
pretty certain this isnt the case on MK2 setups?

[tony_ack]

1. dont agree with this at all, letting a car coast at idle will use less petrol than leaving it in gear. However doing this isnt safe as you dont have proper control over the car. I certainly wouldn't coast down a hill!

It depends on the injection system, modern injection (perhaps digi) are smart enough not to inject fuel when there's no throttle and let the wheels turn the engine over to prevent stalling. Stick it in neutral and then the engine has to supply fuel to prevent it from stalling.

I'm pretty sure this is the case on most modern fuel injected cars, and on the Digifant. If I recall correctly, there's a throttle switch closed instruction on the ECU which will shut off fuel to the injectors above a certain RPM if no throttle is applied.

If you use the instant MPG reading on the MFA secret menu, the reading will do to 99.9 if travelling in gear with no throttle

Though if Johnny is wrong for the first time ever, surely the rapture isn't far behind... 

[Ninja]

Well, I did a propper test of £20 (some harsh driving, some eco driving) - basically a normal £20's worth. I got 110 miles out of her. Which obviously is not 7 (or even 5MPG)

I get that at roughly 19 litres or 5 Galons - which eaquls 22MPG ish. So, my question is - why is my MFA reading 9.7ish MPG average since last reset? Odd..

[chrismk2boyd]

make sure your vacume pipe from back of clocks has no slits or leaks in it and clean, thats first point of call , try attaching another earth to back of clocks running to bulk head , check bonnet earth strap as well, can cause problems.

[rubjonny]

ok fair enough, looks liek I was wrong, not the first time and wont be the last! sorry ben