Trip computer mpg 18% down - ideas?

[cainey]

Hi all

 

just had major surgery on the vrs, head gasket and the usual associated stuff, cam belt etc.  The car now drives like a dream, probably now getting the full benefit of the remap for the first time in I would guess 2 or 3 years!

 

I was worried about the apparent change in the fuel consumption, the trip computer has read an average of 39mpg over the last 150 miles, a mix of urban and dual carriage way - on my work commute, 20 miles door to door, 5 miles of back roads and 15 of dual carriage way I was struggling to get 40 mpg on the readout whereas I would typically be high 40s.

 

That said now that I've plugged some actual figures into excel it turns out that the average was actually 47mpg - ie pretty much what I had before the work.

 

So the question is can anyone help me account for the fact that there is now an error of 18% when my average error over the previous 3 years was less than 2%.

 

I know 150 miles isn't a lot to go on but I am starting a long round trip tomorrow of approx 800 miles so will have a better set of numbers when I get back.

 

Cheers

[felicia16v]

could be the cam timing is slightly different to before? maybe the fact it's running better means you may be making more use of the power?

[DanHam]

I noticed this since I've had my hybrid......reason is because I'm more eager to plant it!

[wja96]

I don't know what year your car is, but the ones with BLT engines have nonsense fuel economy readings on the trip. 20% wrong is pretty normal. ASZ engined cars are usually very accurate. Did they update the ECU as part of the service?

[cainey]

I don't know what year your car is, but the ones with BLT engines have nonsense fuel economy readings on the trip. 20% wrong is pretty normal. ASZ engined cars are usually very accurate. Did they update the ECU as part of the service?

 

The car is 04, I am embarrassed to say that I don't know the engine code - the ECU wasn't touched. 

 

@DanHam and @felicia 16v - the grin factor is well and truly back and the right foot is probably a bit heavier than before!

 

Thanks for the input - I'll update with more figures early next week.

[Dark_Hero]

Winter fuel?

[RAPTURE]

My ASZ is the same.  Winter fuel does drop the mpg a little as does the cold weather, but this does not account for the descrepency of the display mpg.  I have noticed at some point a garage must have removed my clocks.  There is a little bit of paint chipped off the surround of the clocks where someone has prised them out and one of the plastic legs that screws the clocks in place is snapped.  I have done all the servicing on this car scince a garage changed the cambelt at 50k.  That's the only time I can think of that the clocks could have been removed.  But why?.  My mpg has never been as good scince this belt change.  I used to see 60 mpg+ on the dash and performace was amazing, now I struggle to get 40 odd on the same journey.  My cam timing is spot on according to skoda and vagcom +0.5.  I changed every filter and sensor apart from the map sensor due to its location but still my mpg on the computer is still bad and real life not alot better.  Mine is 04 plate also so yours will be a ASZ.  As always any advice appreciated.

Edited 27 December, 2013 by RAPTURE

[eric87]

Hi how would I go about checking my cam timing using vag com? My mate has the program and cable, I just need a procedure for him

[sepulchrave]

Hi how would I go about checking my cam timing using vag com? My mate has the program and cable, I just need a procedure for him

 

Seek and ye shall find!

 

http://www.briskoda.net/forums/topic/297581-just-did-my-cambelt/

Edited 28 December, 2013 by sepulchrave

[RAPTURE]

This video shows how to check and adjust timing on a PD lump :

[theezenutz]

My ASZ is the same.  Winter fuel does drop the mpg a little as does the cold weather, but this does not account for the descrepency of the display mpg.  I have noticed at some point a garage must have removed my clocks.  There is a little bit of paint chipped off the surround of the clocks where someone has prised them out and one of the plastic legs that screws the clocks in place is snapped.  I have done all the servicing on this car scince a garage changed the cambelt at 50k.  That's the only time I can think of that the clocks could have been removed.  But why?.  My mpg has never been as good scince this belt change.  I used to see 60 mpg+ on the dash and performace was amazing, now I struggle to get 40 odd on the same journey.  My cam timing is spot on according to skoda and vagcom +0.5.  I changed every filter and sensor apart from the map sensor due to its location but still my mpg on the computer is still bad and real life not alot better.  Mine is 04 plate also so yours will be a ASZ.  As always any advice appreciated.

I had something similar happen to me. I was always getting 55+ mpg but all of a sudden it dropped down to 40 - 50 mpg. I never had anything done other than the tracking. Strange.

 

Turns out my n/s wheel bearing was shot to pieces. Not saying that's what's causing yours but it may be something to bear in mind.

[cainey]

Just got back from the trip, Ive done the figures for the outward leg as follows:

 

miles on full tank: 395, ~50% motorway, cruising at a frugal 70, ~30% dual carriageway, the rest on A roads, a few little blasts thrown in for the crack! and including an hour sat on the M5!

trip computer mpg: 46.5

Average speed: 48mph

fuel added to first click, (not particularly accurate I realise): 33.18 litres

calculated mpg: 54

trip computer error: ~14%

 

Not as bad as last time, but still a big discrepancy.  I was pleased that the range was still showing at the other end was still 85 miles - so quite good for one tank.

 

Does anyone know what is being 'sensed' for the trip computer mpg calculation, I'd assume it is from the rate at which fuel is being delivered via the pump(s) - in which case if they've all been cleaned up as it was rebuilt the sensor calibration could well have been affected?

[spud31]

Check for rear brake drag, will be more likly in the poo weather were having 

[XLBaconDoubleCheese]

I don't know if I'm missing something or reading the posts wrong.. The OP appears to have a issue where his trip computer is under reading the mpg, yet almost all the replies are suggesting reasons that would be causing low mpg (which isn't the OPs issue).

[Kyle_vrs]

I have this same problem since doing my timing belt although I know the timing is 100% as I've checked on vcds. If I work it out on fully I will get for example 52mpg but the computer will say 46. The mpg isn't actually any worse just the computer now under reads by alot

[JoshH]

On the mk1 TT you can alter the mpg readout through VCDS, I wonder if the same method can be applied to your fabias, may well be worth a shot!

See here and see what you think...

http://www.ttforum.co.uk/forum/viewtopic.php?f=2&t=184040&start=0&hilit=dis+mpg

[armstrong21490]

Better to be under reading than over reading I would say. Mine is the opposite way around. Over reads by about 15%