How do I lose 50 miles per tank..?

[ShaneyB]

Hi all,
Car has been running great but over the last two weeks my fuel seems to be disappearing..? I'm now only getting 200 miles per tank as opposed to 250 a couple of weeks ago..? I'm not driving any differently, have an MRC remap, exchanged MAF and new DV's but puzzled. I am running Total Exellium and filling up at the same garage every time. Could their pumps need recalobrating..?
Any advice would be great.

[Olly_K]

does your fuel gauge read full when you've filled it up ?
if it does then i could be your MAF again, I had 3 MAFs in one day at AmD, does it feel down on power at all ?

[derdle]

Colder weather of late...more "choke"..more fuel? Might be a contributory factor depending on type of use.

[ShaneyB]

Men,
Olly, yes a little down on power and no, it doesn't quite go to as full as it always has. I'm using the G-Spot button when filling but when I fill it just doesn't seem to take anywhere near as much fuel..? My trip used to show I had in excess of 300 miles in the tank when I filled but now it only shows 230 max and that's when I've been putting little dribbles in at the end.
Derdle, Not thought of that and it is the first winter I've had the car. 50 miles though..?

[derdle]

Sounds to me like a faulty fuel sender.... I had a Saab once (no mocking please) and I thought I'd bought a pup cos I only got about 200 out of the first tank of fuel then realised I could only get about 30 litres in the tank. So the sender unit was registering "full" properly but was reading "empty" when there was about 1/3rd tank full left. So when you fill up from "empty" are you putting in 50/55 litres (can't remember what the S4 tank holds) or something like 40/45 litres a time? If the latter this would seemt o indicate that there is loads of fuel in the tank but the sender/guage is telling you it's empty.

Just another thought!

[ShaneyB]

Thanks Derdle,
From empty (5 miles showing available) I'm getting about 52 litres in when it's a 62 litre tank.

[Olly_K]

yeah that sounds right, mines been at AmD for 4 months now but iirc mine used to take about 58 litres

[KayGee]

Sounds like fuel sender, had a new fuel pump fitted? Sender might not been clipped in properly? 10 litres is @ 2 gallons = @50 miles. Unless off course you always put @ 50 litres in, in which case....

Other possibilties are O2 sensors, ECU temp sensor (not dashboard value....) and EGT sensors.

Got VAGCom? do logs for block 1 (engine temp), block 3 (maf) and block 31 and 32 (o2 values).

If engine temp is reading too low, car will run rich permanently thinking it us under startup conditions. MAF should be around 250-260 with custom remap. O2 values better of speaking with MRC to confirm your values (depends what AFR it was mapped for), or better yet if you are local pop over and get them to put the wideband o2 sensor on it.

Should feel really strong currently with all this cold air, however you might just be getting used to the extra HP.

[ShaneyB]

Sounds right or up the creek..? I have in the past been getting around 58 litres in at the same stage so I feel something is wrong.

[ChipHazzard]

Mine appears to be suffering from the same problem over the last couple of tank full's that i'm only getting 200 miles and refilling with approx 50 litres. I did wonder if it was down to the A/C working harder in the colder weather ??

[fade2grey]

The AC should refuse to come on when it's really cold..

Mine is doing about 21-22mpg at the momen, when it used to do 25+ - I put it down to the cold weather but haven't cleaned my maf yet.

[flat6]

Might sound daft but have you checked your tyres pressures recently? A couple of mine were gradually losing pressure and it made a hell of difference to fuel consumption...

[QuantumJohn]

Why not check the fuel consumption instead of just how many miles to the tank?
If it's still doing 20+ miles to the gallon then there's nothing wrong with the engine.

John

[confusionhunter]

I havent done any in depth analysis on the S4, but I did a full electronic analysis of my old tuned G40. Used to return 30mpg at least but dippped to 25mpg....and the AFM started to do funny things. Thats seemed ok for a tuned car but I knew something wasnt right.

I spent a fair old amount of time determining the cause. I even measured voltage drops to the fuel pumps!!
Anyway it turned out to be a below perfect earth. I choose my words carefully as the earthing point for the lamnba sensor seemed ok and a test light wouldnt pick the fault up. But basically it was the earthing point for the lambda. I ran a fresh earth cable straight from the battery to the earthing point and the AFM and that solved the problem! The car ran perfectly after that.
Kept returning 34mpg!!!
Anyway, my point is that there could always be an electroinc bug causing the problem. Another common VAG problem (well VW) is the ECU engine temp sensor starts to read too cold and the ECU makes the mixture a touch richer, meaning less MPG, but is only noticable when the sensor REALLY screws up and the cars runs so rich that you run to the nearest dealer....
My 2p....

[ChipHazzard]

I filled up again with the dash saying 5 miles to go and still only managed to get 51 litre's in. Then i reset the computer and so far in the 50 miles i've done it's telling me it averaging between 18 & 19 MPG. I know some of this is probably due to the fact i'm in rush hour on the A2 / Blackwall tunnel but even on a relatively congestion free run it still seems low to me