Why is my car using ALOT more fuel these days?

[Jamie]

Hi

Had my car in at B & W Auto Repair in Hounslow on saturday to read fault codes and hopefully fix my hesitation issue. Hooked up the Autologix box and no faults - damn i thought. So with the engine running, Jayson had a fiddle around and then all of a suddent the car cut out. Humm - he showed me what was causing the hesitation - the pipe connecting to the engine from the air box with holds the MAF was loose - which explains whilst under hard acceleration - when the engine moves around, it was hesitating.

So he secured that and hey presto - no more hesitation.....however, my car is still drinking more fuel - why?

I took my car into the garage on a full tank. Before i had filled up the OBC said i had done 330 miles from empty (318ci N42) - when i used to get at least 420-450 say this time 2 months back.....I was expecting that with the air box sorted my MPG would go back up - but my OBC still says im expecting to get 350 miles from this tank ful....why?

Could something else be on its way out? Like i said, car drives fine - just shocking MPG from a 318ci
Should i clean the MAF?
Can i do the battery disconnect to make the ECU re-learn?

Thanks

Jamie

[mysticm3]

not too sure my car always uses more petrol in wintery conditions

[Auryn]

no idea mate but what i will say is dont ever by a V8.....i get about 250 miles to a tank if im lucky!

[benny boy]

You should be getting more than that off a 318 but mine gas been using more fuel since it got cold could be down to the cold weather tho i hope so mate

[RDG 40]

If memory serves me right thats what mine comes out at on a full tank so i dont think you have too much of a problem.

My dealer the other day said I myt have a faulty airmass meter due to flucuations in the air flow that didnt show up on the diagnostics i duno that might be worth a check??

With the engine being valvetronic it does remap itself (someone correct me if im wrong) so if you are driving harder these days that maybe the answer to lower mpg??

[donut]

I get about 180 miles round town on a tank, or about 360 if its all motorway work... Although it takes a while for the computer to catch up with itself too so hopefully you should see your mpg rise a bit.

[Jamie]

mystic - hum, the reduction in MPG has been while it was warm also, but yes - predominantly during the colder times

RDG40 - 6 months ago i was defo gettin 430-450 on a tank - perhaps there is somthing we BOTH need to check out on our n42. Seriously, i have to keep a fuel log for work and can see the decline!!!

Faulty airmass meter could be related as im thinking the car is running rich/lean cos of a starvation of air - expecially since no faults are showing on diags....hummmmm

donut - aint yours a 540? 180 around town and 360 on the mway - thats some difference

[Kin Mak]

02 sensors?

[adood84]

did you reset the MPG after the problem was fixed? could be your right foot give it a couple of days and see if it goes back up to normal levels

[RDG 40]

difficult one,

Fas what do you get out of yours buddy??

[Moe]

I never get above 18.9 mpg and when i got the ac on goes to 16.7 the best i seen is about 22mpg on the motorway

[RDG 40]

Just been googleing and researching and found we both may have the same problem in that it is the air mass meter although you would have to have you flow checked first.

The unit is a BOSCH and seems to be around £100 to replace il find out for def and let you know.

My car does seem sluggish at times but i always put it down to it being a 318.

[mystic sport]

Moe, either your accelerator is welded to the floorboards or your car is shagged. My 318ci eaily got 40mpg without even trying, got over 50mpg on runs. I would guess that either the MAF is going flakey or the adaption values need to be reset after the air inlet pipe was secured. Make sure if the MAF is replaced to get the adaption values reset, it is important that this is done.

[Juber]

Bloddy heck Moe, i get 23mpg in town in my 330, and abround 33 on motorways and thats doing 80-90.

[Moe]

But this is the case on my old car and my new car and my new car is a 04 plate with low miles, i do drive a bit right foot happy so i think its just my driving style also i havent made no engine mods to it and o the motorway im talking botu a ton as a average speed

[Jamie]

Moe, either your accelerator is welded to the floorboards or your car is shagged. My 318ci eaily got 40mpg without even trying, got over 50mpg on runs. I would guess that either the MAF is going flakey or the adaption values need to be reset after the air inlet pipe was secured. Make sure if the MAF is replaced to get the adaption values reset, it is important that this is done.


Good post - was it an N42?
Mines is saying 30mpg average and thats with average MPH 20mph (drive to work). Be interesting what happens on saturday when i do a long 150 mway drive...

Even at 30mpg x 14 gallons (i think this is right) thats only 420 miles....yet i know i have had more out of it (combined city/mway driving) - either my OBC is inaccurate or my fuel tank is bigger....???

Could it be that my MAF is causing poor MPG? Or as RDG 40 says, more likley to be the mass air flow meter ? I know i can go back from diags AGAIN but since no faults show up - its hard to work out. How can i find out acceptable tollerance levels for readings? I was watchin the guy with the DIAG machine and saw lots of interesting numbers - be nice to understand what they means etc etc - any links?

As for the adaptation values - i think this was what the guy DID NOT do at the end before he unplugged the machine. I saw the option, but he was clearing fault codes (the 27 odd the ECU remembers each time you try and replace a buld when the ignition is on) and asked me to remind him to 'reset the engine values' - but i forgot...

Is there another way of doing this? Unhook the battery perhaps?

RDG 40 - let me know your thoughts after reading this post....im curious now!!!!

Thanks

Jamie

[adood84]

Just been googleing and researching and found we both may have the same problem in that it is the air mass meter although you would have to have you flow checked first.

The unit is a BOSCH and seems to be around £100 to replace il find out for def and let you know.

My car does seem sluggish at times but i always put it down to it being a 318.

is that same as teh MAF or is it something else?

[Jamie]

is that same as teh MAF or is it something else?

Yea good point - im unsure on this one also..

also a pic of the actual item would be very useful - i think this is the actual bit on realoem

http://www.realoem.com/bmw/showparts.do?model=BV72&mospid=47611&btnr=13_0949&hg=13&fg=15&hl=1

[RDG 40]

they did check and reset adaptation valves on mine, but they still think it needs a new air mass meter, although they did say unless the light comes on again or i notice a drop in performnace then it will be ok, no point in replacing something if its managing ok.

Il have a look at my mpg today and see, if i can il try fill her up too.

Paul what is the criteria for reseting the valves, should i have done them when I put on the CAI and it holds an air meter thing in it?

[mystic sport]

Good post - was it an N42?

Could it be that my MAF is causing poor MPG? Or as RDG 40 says, more likley to be the mass air flow meter ?

Yes, I had one of the first valvetronic 318cis back in 2001.

MAF and mass air flow meter are the same thing.

[adood84]

believe me the MAF(Air mass) doesn't cost 100GBP only , when I had mine replaced under warranty I checked the price its about 300GBP

http://www.realoem.com/bmw/showparts.do?model=BV72&mospid=47611&btnr=13_0949&hg=13&fg=15&hl=1
its number 1 on there as the MAF comes in one part with the holder thing they don't sell them separately

[RDG 40]

well ive had a little drive round town tonight and im getting around 19-24mpg thats driving at a moderate rate.

So hope that helps a bit?

I get major discount rates from a mates garage adood thats the only reason why, can get a diagnostic check for free if needed lol

[Jamie]

well ive had a little drive round town tonight and im getting around 19-24mpg thats driving at a moderate rate.

So hope that helps a bit?

I get major discount rates from a mates garage adood thats the only reason why, can get a diagnostic check for free if needed lol

Humm - mine is reading 28.8 and thats after i reset it last week after filling up....its telling me im gonna get about 410 miles from this tank (and i put a full tank in)

I'll report again after the weekend once ive spent 300 miles on a mway

Oh - if i do end up needin a MAF - can you get 2 at your "major discount rates " ?? :D :D

[Jamie]

Moe, either your accelerator is welded to the floorboards or your car is shagged. My 318ci eaily got 40mpg without even trying, got over 50mpg on runs. I would guess that either the MAF is going flakey or the adaption values need to be reset after the air inlet pipe was secured. Make sure if the MAF is replaced to get the adaption values reset, it is important that this is done.

Could you advise how i can get 40-50 MPG? I presume you had the same car as under discussion here right? 318ci 2.0 Valvetronic? What year as that car?

So if i understand right, that car was giving you 14 (gallons in a full tank) x 40 MPG = 560 total miles at a minimum and 14 x 50 = 700 ??

Yes, defo something wrong with Moe's vert

[Jamie]

Humm - mine is reading 28.8 and thats after i reset it last week after filling up....its telling me im gonna get about 410 miles from this tank (and i put a full tank in)

I'll report again after the weekend once ive spent 300 miles on a mway

Oh - if i do end up needin a MAF - can you get 2 at your "major discount rates " ?? :D :D


OK OK - Update time.

Last tank i got 410 miles after a decent stretch on the M1 (300 miles city driving and then the rest on the MWAY to get this figure) - so looks like the problem WAS the loose intake pipe!!

Filled up again and OBC said i was going to get 440 from empty - lets see how that goes.

MPG is averaging around 31. 38 on the MWAY and 29-31 city driving...

So RDG 40 - i reckon you defo need to check your intake pipework and or the MAF is indeed buggered.....

Jamie

[BigFas]

difficult one,

Fas what do you get out of yours buddy??

Sorry, just seen this.

Around town I get 22mpg. On motorway i get 31+mpg

[RDG 40]

yea thats exactly what im getting Fas cheers dude.

[Jamie]

yea thats exactly what im getting Fas cheers dude.

Surly yous should be returning roughly the same as mine? Fas's should be consuming a bit more due to it being a vert.

Also are these figures with AC on or off ?

My OBC is now saying im gonna go 450 to the tank and my average MPG is 33

Cheers

Jamie

[RDG 40]

i run same exhaust and filter though so may affect it. mine is to the mile the same as fas's

[Moe]

As fas posted my car is giving me the same figures as him and i mean nearly exact as him, imo i floor my car a lot even in city driving so therefore that is why i consume more petrol than you guys as i hardly even change gears at 3k rpm so that is why i consume more fuel.