Fuel consumption

[APinto]

Hi there!

I'm the proud owner of a Mk3 GTI 2.0. I use it to commute, driving around 50 miles per day. So, I know pretty well it's fuel consumption habits, which for an economy style of driving sit between 38 and 40 MPG.

The problem is that a few weeks ago it suddenly started to consume more. I usually can reach 400 miles with a full tank, but that time I barely made it over 300 miles. And it's like that since then... Currently, it's in the red zone with only 280 miles... 

I took it to a friend mechanic that plugged-in into the computer to check if there was something wrong. But the returned code indicated no errors... He attributed the situation to the automatic-choke, saying that it can cause the car to consume more when the weather is cold. I accepted it, reluctantly, knowing that a 1/4 increase in fuel consumption is way too much...

The weather is warmer outside now but the car is still drinking like mad. Can any of you guys help me? Did any of you ever experienced a similar situation?

Thank you very much for your help, cheers,

AP

[Andy-H]

I have just recently had my car through the MOT.

Before it went, we did an emmissions check and it showed it to be overfuelling  .

A quick check found that the lambda sensor in the exhaust was faulty, sending the wrong information to the ECU.

New lambda in and some tweeking with the fueling and, although I don't completely trust the MFA, it now reads between 8-10MPG more than it ever has. Hopefully  time will tell if it is actually improved.

Other than that, when was the last service, including air filter, plugs etc. Throttle body could be full of crud 

Andy.

[zdebx]

Not trying to hi-jack the thread, but I've got a similar problem. Mine's not a GTI, it's a 1.8, but I think it "drinks" petrol like GTI, lol

I put £20 of petrol, which is roughly 18 litres, and I drive 50 miles (regular city driving)...Is that normal? Lasts me for about a week, so every week £20 (20x4) - that's a fooooking £80 a month just on petrol. Maybe I'm mistaken and that's ok?

[javalin]

worth checking the coolant temperarture sensor - if its not reporting the engine warmed up, the ECU will overfuel

James

[oggy]

Yup - Fair comment from your garage man - but only in the time taken it takes for the engine to warm through obviously. Seems like current consumption is excessive.

Agreed that with care I too obtain @ 40mpg - which to be fair is astonishing for a 13 year old 2 litre car

Agree with all other recommendations plus change out the ECU relay itself - they are known to decay a little over time before they finally pop - then the engine fails to start. For £15 or so worth the effort and it's a 5 minute job - ensure you obtain the genuine VW part.  Shove the old one in the glovebox as an emergency spare.

Incidentally Lambda sensor can be a swine to change as it sometimes welds itself to the manifold - do take care here and soak with ease-it fluid or similar first.

[APinto]

Thank you very much! I really appreciate your contributions, I'll pass them to the friend mechanic.

One thing that I forgot to mention: yesterday I drove for half a hour, then stopped the car and tried to start it a minute later. It didn't start, I could hear the starter motor and a weird "mushy" sound (sorry, that's the best word I can find). Tried a second time, this time after pressing the immobilizer button in the key chain and nothing again.

I though to myself: this isn't bad, at least now I know that there's definitely a problem! Tried a third time after a few seconds and the car started.

I had to stop the car a few minutes later and it started normally. This morning it didn't give me any problem, either.

Do you guys thing that this might be related with the fuel consumption problem?

Thank you very much again, cheers,

AP

[oggy]

Ahem -- see last post ref ECU relay! If not, get garage to test Hall sender - in distrubutor, and change that for starters if it is a dud...

[APinto]

Hello!

Based on your contributions and those of a friend of mine, I'll change the following parts:

Coolant temperature sensor
ECU relay
Lamba sensor

Hope this helps, lately when I step on the accelerator it sounds like pound coins hitting the asphalt! :-)

Thank you,

AP

[axewielder]

i know ecu realy wont show on diagnostics but wouldnt lambda+ temp sensors be pretty obvious, even if they didnt show as fault codes it should be clear if they are giving dodgy results from reading the relevent figures
your recent sound is either the usual mk3 exhaust blowing/rattly heat shield or could be the destructive knocking/detonation, hopefully not though especially if its overfuelling

[mac7]

your recent sound is either the usual mk3 exhaust blowing/rattly heat shield or could be the destructive knocking/detonation, hopefully not though especially if its overfuelling

If the manifold gasket was blowing, it might allow air into the exhaust stream. The lambda sensor will measure more oxygen in the exhaust gas and tell the ECU to pump more fuel in as a result - hence the high fuel consumption.

Just a theory.