Massive rise in fuel consumption

stubby276

Active Member
May 4, 2021
40
29
Has anyone had an issue with sudden rise in fuel consumption? Happened after I filled up this week, with range on full tank dropping from 455miles to 355 and then 280 after I tried to clear the issue by filling again, but seems to make it eorde
Car is MY22 Formentor V2 190, 15000miles and is otherwise driving fine. My driving style hasn't changed.
Screen shot shows my average mpg for each refuel..the last 2 stand out somewhat!!
I am presuming a problem with sender unit?
 

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DEAN0

Old Git
Feb 1, 2006
5,315
323
Preston - UK
Mine did this as the particulate filter started getting full.
Then I got the warning on the dash to take the car for a run to regen the particulate filter.
After the regen - fuel consumption went back to normal.

Also - with this colder weather - the modern car uses more fuel when started to heat up the particulate filter.
 

SRGTD

Active Member
May 26, 2014
2,457
1,337
Yes, I was thinking it’s probably the GPF (gasoline particulate filter) going through a forced / active regeneration.

When the GPF was going through a regeneration in my VW (2.0 litre 200ps EA888 gen3b engine) it was very noticeable it was happening. Tell tale signs were;
  • deeper, gruff exhaust note
  • a slight hesitancy when moving off from rest, a slight lumpiness to the engine at idle speed and a reluctance to accelerate
  • a ‘hot’ smell (not sure it’s possible to smell heat 🙂)
  • significantly worse fuel consumption during the regen process.
It took around a 1/2 hour for the regeneration to complete; once it was complete, things were back to normal.

The frequency of forced / active regenerations will be influenced by journey types driven; a car covering lots of short journeys on a cold engine is likely to experience more frequent GPF forced / active regenerations than one covering predominantly long(er) journeys with the engine up to optimum temperature.

Agree that the colder weather will also adversely affect mpg, so a GPF regeneration during the winter months will be a double hit to fuel consumption compared to summer fuel consumption.
 
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stubby276

Active Member
May 4, 2021
40
29
Thanks for the responses. Would my car even have a particulate filter though ( being petrol). It happened instantly after refuelling and did 2 journeys that day of 70miles (90minutes) so that would have been enoigh time if that was the case (according to my experience of previous diesel car)
I agree re colder weather but a drop from 35mpg to sub 25mpg seems VERY extreme
 

stubby276

Active Member
May 4, 2021
40
29
Just to add further. The car is driving fine with no obviois difference in feel/sound. When I filled up to see if it would correct things it said I had mpg of around 24 but the amount it took to fiill worked out to 30mpg (still worse than usual but j)had been stuck in traffic for ages)
 

SRGTD

Active Member
May 26, 2014
2,457
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VW group started fitting gasoline particulate filters to their petrol engined cars in 2017 / 2018 so yes, your car will have one.
 

dashnine

Active Member
Oct 31, 2012
424
164
Warwick, UK
GPFs in a petrol car don’t actively regenerate (by burning additional fuel) like a DPF in a diesel car as the exhaust temperature on the petrol is much higher.

The cause of the excessive fuel consumption must be something else - and wouldn’t be that high (if the car were a diesel) anyway.
 

stubby276

Active Member
May 4, 2021
40
29
GPFs in a petrol car don’t actively regenerate (by burning additional fuel) like a DPF in a diesel car as the exhaust temperature on the petrol is much higher.

The cause of the excessive fuel consumption must be something else - and wouldn’t be that high (if the car were a diesel) anyway.
Thanks. Thats my feeling too. I've had no message about taking it out for a spin to burn off either. Another call to the garage I reckon.
 

Andy.M

Active Member
Mar 20, 2022
258
119
Have you done a manual mpg check to compare it with the on board computer?

I,m surprised to learn of petrol particulate filters. I though I’d left all that behind with my last diesel Evoque and the problems it threw up.
 

dashnine

Active Member
Oct 31, 2012
424
164
Warwick, UK
Have you done a manual mpg check to compare it with the on board computer?

I,m surprised to learn of petrol particulate filters. I though I’d left all that behind with my last diesel Evoque and the problems it threw up.
I had a diesel Discovery Sport with the same design **** up and subsequent DPF location (except it wasn’t just a DPF). I got the free oil and filter changes out of Land Rover but then chopped it for a petrol DS before the DPF, EGR and oil dilution issues became a financial liability.

To be fair the GPF is nowhere as problematic as a DPF (needing active regen etc.), the main impact being it muffles the exhaust note further.
 

Doogle

Ageing rocker🤟🏻🎸
Nov 25, 2021
228
102
Cumbria
Tbh, I do find occasionally my MPG, and available tank range can vary quite a lot from run to run (or day to day) I'm not sure if it's more to do with how the car calculates the figures than real time use, I've found sometimes my available range can be say 325 miles, then after setting off and driving for a while the available range has gone UP to say 330-335 miles, along with mpg improving?
I do think shorter journeys make both figures look out personally?😶
 

stubby276

Active Member
May 4, 2021
40
29
All sorted!!!! Thanks to SRGTD and others for pointing me in the right direction. I filled up this morning again and my MPG was still low 20s but then a 2hour blast down the M62 with some foot off the pedal episodes has given me a very respectable 39mpg for the journey. I looked up the 'issue' in the Formentor manual where it details exactly this process.
In hindsight, perhaps my driving style to work and back (20minutes mostly at 30mph) and with mrs in car (constantly reminding me what the speed limit is and having a fit if feels ANY acceleration) doesn't really allow me to get the car warmed up enough to burn off.
Happy days.
Thanks again
 

SRGTD

Active Member
May 26, 2014
2,457
1,337
All sorted!!!! Thanks to SRGTD and others for pointing me in the right direction. I filled up this morning again and my MPG was still low 20s but then a 2hour blast down the M62 with some foot off the pedal episodes has given me a very respectable 39mpg for the journey. I looked up the 'issue' in the Formentor manual where it details exactly this process.
In hindsight, perhaps my driving style to work and back (20minutes mostly at 30mph) and with mrs in car (constantly reminding me what the speed limit is and having a fit if feels ANY acceleration) doesn't really allow me to get the car warmed up enough to burn off.
Happy days.
Thanks again
Good to hear it’s sorted 👍.

I periodically do the ‘foot off the pedal episodes’ in my car when the engine’s fully up to temperature. From discussions on one of the VW forums it was said that as the car decelerates with the foot off the pedal, excess oxygen is drawn in via the exhaust which helps aid the process of burning off the soot in the GPF.
 

Doogle

Ageing rocker🤟🏻🎸
Nov 25, 2021
228
102
Cumbria
All sorted!!!! Thanks to SRGTD and others for pointing me in the right direction. I filled up this morning again and my MPG was still low 20s but then a 2hour blast down the M62 with some foot off the pedal episodes has given me a very respectable 39mpg for the journey. I looked up the 'issue' in the Formentor manual where it details exactly this process.
In hindsight, perhaps my driving style to work and back (20minutes mostly at 30mph) and with mrs in car (constantly reminding me what the speed limit is and having a fit if feels ANY acceleration) doesn't really allow me to get the car warmed up enough to burn off.
Happy days.
Thanks again
So this IS ACTUALLY a thing it seems, certainly something to bear in mind🤨🤔
 

Andy.M

Active Member
Mar 20, 2022
258
119
You've lost me now. Foot off the pedal process in the manual?
Where in the manual will I find it, had a look and cant seem to see it.
 

martin j.

Active Member
Feb 11, 2007
1,996
891
Fife
I often get the situation where after a refuel the range indicator won’t change until 100 miles or so are covered, seems the range at refill will use recent mpg to calculate what it thinks car will do.
 

SRGTD

Active Member
May 26, 2014
2,457
1,337
You've lost me now. Foot off the pedal process in the manual?
Where in the manual will I find it, had a look and cant seem to see it.
It’s under ‘Particulate Filter’ in the owner’s manual - page 309 in the June 2022 edition. If yours is a different print date, the particulate filter section might be on a different page, so check the index at the back of the manual for the page number.

09EAA0D5-AF16-49E3-8EA1-5A0D9E5610C7.jpeg
 
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Doogle

Ageing rocker🤟🏻🎸
Nov 25, 2021
228
102
Cumbria
It’s under ‘Particulate Filter’ in the owner’s manual - page 309 in the June 2022 edition. If yours is a different print date, the particulate filter section might be on a different page, so check the index at the back of the manual for the page number.

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Glad you posted this, being on a "Poverty entry" 1.5 I'm guessing this is nothing for me to bother about😆👍