e39 mpg

[Scamp's Walker]

Am having various electronic glitches at the moment and am trying to work out which "bits" are working. Just done a long motorway run between 60-80 mph and car is returning, according to the computer, 30 to 32 mpg (it's a 523i auto). Does that seem about right, car seems to be abusing petrol at the moment but seems fine on a long run, if the 31-32 mpg figures are correct! Also does anyone have the real figures that the car should be returning? Also RANGE unexplicable dropped from 80 to 55 to 40 in the space of 3-4 miles once off the motorway, does that seem normal, or are they just "sensitive" when they get low?

Alternatively, am I having air flow meter issues?

Edited by Scamp's Walker on Sunday 24th February 23:30

[Kinky]

My average MPG on my E39 523i auto touring is 23.3.

I do tend to watch the mileage quite carefully - but I've never seen it react like yours had.

K

[Scamp's Walker]

Thought mine may be erratic, thought it was a "senior" moment but the computer and dashboard etc seem to be having communication issues at present!

[Chromofoam]

Try getting a little electronic lubricant and cleaning your MAF Sensor - unscrew it carefully and spray it with a bit of the stuff - be careful, its delicate - and make sure it's thoroughly clean of any gunk or particles. try not to touch it but if you must use paper towel - DO NOT USE BOG ROLL! I made that mistake, it covers everything in fluff

that should eliminate one possible cause of the problem - I need to do it to mine as well because its returning funny figures after a fuel system revamp. Fun!

[Scamp's Walker]

Local indie has offered (for a fee) to "do a diagnostic" for me so that we can rule out various componemts as some sensors are prone to failing, or so he informs me.

That said, is 30 mpg about right or thirsty, based on people's ownership as oppposed to BMW figures....!Overall it worked out at £30 worth of petrol for 150 miles of motoring!!!

[Neil.D]

You need electrical contact cleaner for the MAF, not lubricant if you're gonna give that a go dude.

Edited by Neil.D on Monday 25th February 08:03

[Scamp's Walker]

Where can you get the cleaner from? What are the symtoms of MAF problems? And how do you really diagnose them?

Edited by Scamp's Walker on Monday 25th February 09:41

[Chromofoam]

sorry - i meant cleaner

My mistake.

I bought some from Halfords for somethin like 3 quid.....it's called *runs to look at tin* Halfords Electrical Contact Cleaner, and it comes in a green and yellow spray tin (about the size of WD40) with a little red straw.

should do the trick.

If your MAF is gunky then the ECU might think that you're getting limited or inconsistent airflow and as a consequence the engine will run lumpy or stall frequently. It's just a case of fault finding really - if you clean the MAF and there's no improvement, try something else - cant do any harm to give it a clean.

I recently had to do it because my 540i LPG is overfuelling on LPG so it gunked up the MAF and the spark plugs - the petrol pump had broken so I was running it on LPG for a while - now that I've replaced the fuel pump, the fuel filter, the spark plugs and cleaned the MAF, she runs luuurvely. It's worth regularly inspecting such parts....say, every 5000 miles take a peek, to a bit of maintenance, do an oil change etc. Can be expensive but it'll prolong the life of your engine!

[Neil.D]

MAFs get clegged up as the air filter cannot collect all the crud going through intake. Sure it does a mighty fine job but after 50k miles or so they can get tiny deposits that build up over time. The wire in the MAF is made of platinum and this corrodes giving false readings to the engine. Also K+N air filters have been know to spray oil over the MAF as it uses oil, coated over the filter to do its job.
The wire is heated up to several hundred degrees C and as air passes over it it cools. Owing to the amount it cools it can determine revs and tempreture which is directly linked to how it fuels the engine. Once evry while the wire will be heated up to 1000C for a seond to try and burn off dust deposits etc.
A gunked up/riuned MAF can cause stalling, unstable idle, reduced performance, limp home mode, fueling problems as described or just a feeling that the car is ''off the boil'' at full chat.

Cleaning a MAF can give them a new lease of life but if they are shot then they need to be replaced.
I take mine out and clean them every month.
Here are some instructions, the only part I dont agree with is dabbing the contacts with 'Q tips'
You dont need to physically touch anything, just spray them off, let it dry (45mins or so) then stick them back in.

http://www.louv.tv/cars/m5/MAF/

Neil

[Scamp's Walker]

The dashboard and computer not communicating has caused me to, very annoyingly, run out of petroland/or to almost drain the tank on a couple of occasions recently, I havn't had to have the car serviced yot and can't confirm the last time the fuel filter was changed. Presumably a dirty fuel filter may be a contributory factor? Are they easy to change as I may as well do it as a "well it's not the fuel filter" option. Car is not running lumpy or stalling but did appear to be running at about 1/3 from cold on the temp gauge whilst doing 80 around the M25 with the aircon on (normally sits just below 1/2). Does that indicate a related problem, the outside temp registered as 11.5 degrees, but seemed colder, and so I guess the wind chill/cold air may have contributed but it's the first time that I had noticed it at that level.

[WindsorRob]

On the MPG front, I have a 523 auto, yr 2000 model. I've done 80,000 miles in it, mostly motorway and I consistently get 30mpg. Trip comp says ave 30.7, snd I've checked it many times.

[miniman]

I have had 2 opinions given to me on the cool running problem which my 523 also has. Most popular opinion (from www.bmwland.co.uk forums) is that the thermostat is knackered. This is a quick job to fix and about £20 for the parts (you need a thermostat, housing and gasket which you can get from www.gsfcarparts.com

Other opinion, from my mate who runs a recovery firm and has thus plucked many 5 series from the hard shoulder in his time, is that its the head gasket. He's tested mine and it's leaking very slightly so he's chucked some "jollop" in the coolant to try and sort it. However it hasn't made any difference so this weekend he's changing the thermostat for me.

Interestingly my range display does seem to fluctuate wildly when the tank is low and when the engine is cold. e.g. this morning went from 35m to 12m during the long journey from the drive to the road in front of the drive

Av MPG on mine is currently sat at 19 hoping it will improve when (a) the stat is fixed and it runs at the right temp and (b) when I do something more than a 5 minute journey to the station. Off to north Wales in it next week so we shall see...

[[TW]Fox]

I agree with the people on BMWLand, if it was your head gasket you'd surely know about it! Your 'mate' might have done more harm than good by throwing stuff into the coolant for you.

[miniman]

I trust him implicitly! He agreed it was probably the stat but checked the head gasket to be safe.

[Scamp's Walker]

Taking the car for a long run tomorrow and will monitor the temp gauge but may replace the stat anyway. If there is a problem it should do it all the time/frequently shouldn't it?

Presumably dealers would just replace the MAF rather than clean it!

[Neil.D]

I clean my MAFS once every 6 weeks or so.

A dealer would charge £200 or so plus fitting for a MAF.