Sudden drop in fuel economy ???

[Bullet]

I've owned my car 2 years and its always returned around around 200-220 miles to a full tank but over the last month the mpg has dropped off every week to the point where i'm now only getting 160 miles per tank ?? thats about 13-14 miles per gallon.

My car was only serviced just before christmas, oil, plugs and air filter and i don't have any lights up on the dash.

 

Anyone got any idea what it could be ?

[Zeezeebaba]

Are you putting a similar amount in when fuelling up. In my case it was a faulty fuel gauge as when I fuelled up from a quarter of a tank it only took about £30 to brim again. Recently the gauge played up again only displaying three quarters after brimming. My intention was to take out the sensors and clean but it's now ok again.

Edited February 23, 2017 by Zeezeebaba

[marzman]

Are your tyres up to pressure?

 

Also, probably not this but fuel economy is always MUCH worse in cold weather... the weather was mild before christmas but much colder since.

[Zeezeebaba]

Otherwise it's over fuelling or leaking somewhere. Leaks in most cases are obvious but the ecu over fuelling due to receiving dodgy info via a sensor is less obvious. Strange you have no cel on if it's over fuelling though.

Edited February 23, 2017 by Zeezeebaba

[Strudul]

Was gonna mention that colder weather = worse MPG, but if you've had it for 2 years (and presumably cars beforehand), then I'm guessing you are well aware of that this time of year.

 

Is the MPG readout significantly lower too?

[Ricey]

Fuel economy if anything should be better in cold weather.

 

Cold air is more dense meaning bigger bang.

 

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[marzman]

Fuel economy if anything should be better in cold weather.

 

Cold air is more dense meaning bigger bang.

 

Sent from my SM-G925F using Tapatalk

 

Performance might be better, but not fuel economy.

 

https://www.fueleconomy.gov/feg/coldweather.shtml

[davey_83]

I had the same problem, on a run my mpg drop'd significantly which was as a result of a split vacuum hose causing the ECU to run rich to save the engine.

[colesl4w]

Very strange. I was thinking that even 220 miles to a tank like you were getting previously is very low. I do short, quick runs and still get roughly 320. What is your usual MPG reading?

[Tricky-Ricky]

Fuel economy will be worse in cold weather, cold air is denser so the MAF is measuring more airflow so adding more fuel = more fuel consumption, however if its making that much difference i would suspect a lambda sensor or dirty MAF.

[davey_83]

Fuel economy stuffers in cold weather due to cold start ups and the length of time it takes the engine to reach correct opperation temp.

[Tricky-Ricky]

Fuel economy stuffers in cold weather due to cold start ups and the length of time it takes the engine to reach correct opperation temp.

 

That's another reason too, however it shouldn't make a vast amount of difference unless temps are sub zero all the time, modern engines are designed for quick warm up and the VQ is no exception with a rad bypass pipe to help, so cold enrichment time in theory shouldn't be a lot different, at least not enough to cause that change in consumption.

[Ekona]

14mpg? Sounds like you're driving it properly

[RobPhoboS]

Try taking the MAF out (need a star socket for it), and use contact cleaner spray over it.

Have a look on youtube to get the idea.

 

My fuel gauge doesn't work properly so I just fill it to the brim, reset the trip and once it gets to around 250miles I fill up again.

It's one of those jobs to do er soon

[MiddletoM]

also worth noting that if you do clean the MAF you will need a security torx bit. Basically a normal torx bit with a hollow centre. I bought mine for 4 quid online and cleaned my MAF a couple of days ago using electrical contact cleaner.

[Zeezeebaba]

I disconnected the battery before doing my MAF and was careful not to touch it. Was I being over cautious or is this the recommended way to do it?

Throttle body needs the same routine though doesn't it?

Edited February 24, 2017 by Zeezeebaba

[RobPhoboS]

I disconnected the battery before doing my MAF and was careful not to touch it. Was I being over cautious or is this the recommended way to do it?

Throttle body needs the same routine though doesn't it?

 

Check the manual but essentially yeah, it's what it says in there.

I don't know if you really have to disconnect the battery, just pull the plug before removing it.

[-Bradders-]

Id say check tyre pressures, i'd never have though they would make much of a difference but blimey, i used half a tank in 5 days worth of 10 mile trips lol... realised my back tyres where low (wondered why it was launching off the lights so well haha) and i manage the same trip in 1/4 of a tank

[Bullet]

I'm a little ocd and check my tyre pressures every second fill up (so once a month), my fuel gauge is working fine and i religiously fill up as soon as the fuel light comes on and brim it.

 

Could it really be caused by a dirty maf ?

[RobPhoboS]

Look on youtube - search there too

[ilogikal1]

i religiously fill up as soon as the fuel light comes on and brim it.

 

That's all well and good, but what's the actual volume of fuel that you are putting in each time? As previously stated a dirty fuel gauge sensor could easily mean you've still got 20% more fuel in the tank when the light comes on and you "brim it".

[Ricey]

Fuel economy if anything should be better in cold weather.

 

Cold air is more dense meaning bigger bang.

 

Sent from my SM-G925F using Tapatalk

 

Performance might be better, but not fuel economy.

 

https://www.fueleconomy.gov/feg/coldweather.shtml

This is why i clean cars and leave the mechanic to fix them 😂

 

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