Engine: B5204: - Massive drop in fuel economy

VolvoReloaded · Sep 14th, 2022, 20:05

Hello,
Recently I have had the dreaded 'brake failure stop safely' problem, but through the process of elimination I am 75% sure it is fixed, new discs, new calipers and pads, new reluctor rings, sensors, even a new hub on one side, and yet until I changed the brake position sensor the problem stayed intermittent. The car is a 2004 2.0T and the work I did on it needed doing anyway, the discs were 8 years old, reluctor rings were in bad shape, because I did the work with a friend and no garage fees it was very reasonable.
Yesterday I drove 330 miles to see my elderly mother and my older Brother who isn't very well, normally on the motorway I can get as high as 36-37mpg if I drive sensible, however yesterday I could only get a very worrying 22mpg, as we all know with all the vast price increases that is impossible to sustain.
I was hoping for any ideas in to why the mpg has plummeted, I have a new MAF on the way but I could be clutching at straws, I am concerned, any help would be very very appreciated.
Thanks in advance

stuart bowes · Sep 15th, 2022, 00:13

Maf is a possible but what else have you checked .. there's a number of variables obviously as I'm sure you know

tyre pressures all good? (I go with 36 on all wheels, but I have XL tyres so that's well within their capability) fuel filter and air filter changed recently? when was the last oil change, and how old are the plugs

After all that brakes work is it possible something is binding, do any of the wheels feel excessively warm after a long drive, does it go in a straight line when you (briefly) let go of the wheel

I don't do turbos but I've no doubt there's things there that can be checked as well others will no doubt add suggestions

any chance of connecting to vida and plotting out a few graphs of sensor readouts that might give people some ideas

Joe Harding · Sep 15th, 2022, 08:04

^^^ MAF +1 If that has gone wrong the engine management system reverts to look up tables. I know because ours went the same way in the hot summer. Cleaning helps but be ready to really slosh loads of MAF cleaner over it.

Georgeandkira · Sep 15th, 2022, 13:52

How many miles are on your 2004? I ask because the upstream O2 sensor (the plainly visible one in the exhaust manifold against the firewall) can perish fast. When mine went @ ~150K I could actually see the gas gauge plummet. They do have a lifespan. I bought DENSO brand instead of Volvo brand (both names appeared on my original sensor) and my bonny fuel use numbers were instantly restored.

What brand of MAF is on the way? I ask because all but dealership and OEM Mass Air Flow sensors are suspect. Remember to let the old one air dry after hosing with MAF cleaner only.....that's because some other electric parts cleaners leave a residue.

Darlo 1 · Sep 15th, 2022, 14:16

Thermostat stuck open? that'll mess with the fuel economey.

Lancee · Sep 15th, 2022, 14:19

Did you change/adjust the handbrake shoes ?

Seems coincidental that after brake work this issue has cropped up ?

Slightly binding brakes somewhere would be my first port of call.

As Stuart suggested "After all that brakes work is it possible something is binding, do any of the wheels feel excessively warm after a long drive, does it go in a straight line when you (briefly) let go of the wheel".

I will say it again, "beware the Rabbit hole""

VolvoReloaded · Sep 16th, 2022, 23:48

Thank you all so much for the replies, I am going to go through all your advice bit by bit then I'll let you know what's going on.

Mileage is 157K

Handbrake done by Volvo in December 2021

MAF should be here 17th September.

New discs and pads, new hub one side, no binding and cool after a long drive, tyres new-ish and pressures fine.

Thermostat not checked it yet but will very soon.

Will get back in a few days, thanks again everyone.

Sep 14th, 2022, 20:05	#1
VolvoReloaded New Member Last Online: May 28th, 2024 18:38 Join Date: Dec 2014 Location: At the moment, Cornwall	Massive drop in fuel economy Hello, Recently I have had the dreaded 'brake failure stop safely' problem, but through the process of elimination I am 75% sure it is fixed, new discs, new calipers and pads, new reluctor rings, sensors, even a new hub on one side, and yet until I changed the brake position sensor the problem stayed intermittent. The car is a 2004 2.0T and the work I did on it needed doing anyway, the discs were 8 years old, reluctor rings were in bad shape, because I did the work with a friend and no garage fees it was very reasonable. Yesterday I drove 330 miles to see my elderly mother and my older Brother who isn't very well, normally on the motorway I can get as high as 36-37mpg if I drive sensible, however yesterday I could only get a very worrying 22mpg, as we all know with all the vast price increases that is impossible to sustain. I was hoping for any ideas in to why the mpg has plummeted, I have a new MAF on the way but I could be clutching at straws, I am concerned, any help would be very very appreciated. Thanks in advance

Sep 15th, 2022, 00:13	#2
stuart bowes trying to be helpful Last Online: Today 01:19 Join Date: Aug 2020 Location: Dagenham	Maf is a possible but what else have you checked .. there's a number of variables obviously as I'm sure you know tyre pressures all good? (I go with 36 on all wheels, but I have XL tyres so that's well within their capability) fuel filter and air filter changed recently? when was the last oil change, and how old are the plugs After all that brakes work is it possible something is binding, do any of the wheels feel excessively warm after a long drive, does it go in a straight line when you (briefly) let go of the wheel I don't do turbos but I've no doubt there's things there that can be checked as well others will no doubt add suggestions any chance of connecting to vida and plotting out a few graphs of sensor readouts that might give people some ideas __________________ V70 '01 auto petrol 2.4 (140) 72k ------------------------- mini project - link Last edited by stuart bowes; Sep 15th, 2022 at 00:19.

Sep 15th, 2022, 08:04	#3
Joe Harding Premier Member Last Online: Yesterday 18:53 Join Date: Oct 2010 Location: Bristol	^^^ MAF +1 If that has gone wrong the engine management system reverts to look up tables. I know because ours went the same way in the hot summer. Cleaning helps but be ready to really slosh loads of MAF cleaner over it. __________________ "The more people I meet the more I like my God."

Sep 15th, 2022, 14:16	#5
Darlo 1 Lunatic. Last Online: Yesterday 22:47 Join Date: Dec 2006 Location: staffordshire	Thermostat stuck open? that'll mess with the fuel economey. __________________ V40 1.9D 2004 620 miles to the tankful. 235000 miles on clock. Now sold, S60 D5 2004. I vape therefore I am.

Sep 15th, 2022, 14:19	#6
Lancee Premier Member Last Online: Today 00:02 Join Date: Jun 2009 Location: Devon	Did you change/adjust the handbrake shoes ? Seems coincidental that after brake work this issue has cropped up ? Slightly binding brakes somewhere would be my first port of call. As Stuart suggested "After all that brakes work is it possible something is binding, do any of the wheels feel excessively warm after a long drive, does it go in a straight line when you (briefly) let go of the wheel". I will say it again, "beware the Rabbit hole"" Last edited by Lancee; Sep 15th, 2022 at 14:22.

Sep 15th, 2022, 13:52	#4
Georgeandkira Premier Member Last Online: Yesterday 12:57 Join Date: Feb 2009 Location: Hackensack	How many miles are on your 2004? I ask because the upstream O2 sensor (the plainly visible one in the exhaust manifold against the firewall) can perish fast. When mine went @ ~150K I could actually see the gas gauge plummet. They do have a lifespan. I bought DENSO brand instead of Volvo brand (both names appeared on my original sensor) and my bonny fuel use numbers were instantly restored. What brand of MAF is on the way? I ask because all but dealership and OEM Mass Air Flow sensors are suspect. Remember to let the old one air dry after hosing with MAF cleaner only.....that's because some other electric parts cleaners leave a residue.

Sep 16th, 2022, 23:48	#7
VolvoReloaded New Member Last Online: May 28th, 2024 18:38 Join Date: Dec 2014 Location: At the moment, Cornwall	Thank you all so much for the replies, I am going to go through all your advice bit by bit then I'll let you know what's going on. Mileage is 157K Handbrake done by Volvo in December 2021 MAF should be here 17th September. New discs and pads, new hub one side, no binding and cool after a long drive, tyres new-ish and pressures fine. Thermostat not checked it yet but will very soon. Will get back in a few days, thanks again everyone.

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