fuel economy question - volunteer required!!!

[m8arx]

can someone test this for me (i feel my car either has a problem with the fueling or another underlying problem)

today, i started the car (210bhp amk s3 with no mods at all).

when driving out of my work car park, i was sitting in first gear at about 1400 revs, and sat at this for about 8-10 seconds and the reading on the MPG average was 9.3.

i then changed to 2nd gear once i pulled onto the main road, and noticed the same, the MPG was below 14mpg below 2k rpm.

this might be coincidence, but when i go above 2k (although not all the time), it goes up to about 35-45mpg.

this is with steady, careful acceleration

if i go on-boost, it obviously will go down to about 20 again (if not less) but i'd expect that anyway - what i don't get is why the consumption is shockingly bad at low revs off boost???

even when i go up normal hills in second gear at about 1500 revs, the mpg seems to read anywhere from 9mpg to about 18mpg.

is something up, or is this normal??????

for info/help - i put 40 quid in the car on thursday night, and this took it to a ballhair off 3/4 of a tank (had a little left in the tank already). i have one 110 miles of motorway/A road driving at around 60mph, coming on boost maybe 4 times in all for about 5 seconds each. i have also done 27 miles town driving, again, very rarely coming on boost. i'm now sitting with just over a quarter of a tank left.

 

[emery1990]

Not sure, but it isnt all about sitting as low as possible on the revs when driving along, ie 5th gear (6th) going 30 mph, itll be very low revs but once you put your foot down the engine will have to struggle to to pick up speed, so i think it has more to do with the throttle position than sitting at low revs.

does it do it when sat off boost for ages?

 

[m8arx]

the engine definately isn't labouring at those sort of revs especially in 1st and 2nd gear! if i was sat in 5th or 6th at 1500 revs then aye, its definately going to have to work harder to get going, but not in 1st, or 2nd gear it isn't.

 

[emery1990]

spose, have you tried it in them other gears? youd have to be going really slow to be on 2nd or 1st gear gear and 1500 revs though. youd spend so little time in that rev range unless purposely doing it going 15mph?

 

[m8arx]

in moving traffic i have had to do it a few times, sitting at around 10-15 mph in 1st and 15-20 mph in 2nd gear.

if someone else with an s3 can confirm if this is what they get, it'll help me understand if this is correct - or if indeed my car has a fueling problem (overfuelling obviously).

i've had it on Launchmaster and it picked up 2 errors, one P0102/16486 maf sensor, but this is quite possibly because i unplugged the MAF for a minute while idling for something else.

2nd error was P1555/17963 charge pressure value above max charge pressure - checked it out on ross-tech wiki and it gives a few suggestions around boost hoses/n75 etc, but i've cleared this and will find out if it's came back tomorrow.

 

[leshkin]

The MPG numbers on the computer are quite a bit on the optimistic side. If you want to find out exactly what MPG your car does in reality, do this:

1. Fill the tank to the top and reset the mileometer to zero
2. Drive as you normally drive for as much or as little as you want - the longer the better. I generally do this this up-to or bellow the half tank mark.
3. Fill the tank to the top again and record the amount of fuel you put in and the miles you did since last fill-up
4. Open the MPG calculator and enter the requested information. It will then tell you your real MPG

I found that this method gives me a consistently worse MPG figure compared to the on-board computer.

I did the same test you described and dd not see the same results.

 

[The Doctor]

for info/help - i put 40 quid in the car on thursday night, and this took it to a ballhair off 3/4 of a tank (had a little left in the tank already). i have one 110 miles of motorway/A road driving at around 60mph, coming on boost maybe 4 times in all for about 5 seconds each. i have also done 27 miles town driving, again, very rarely coming on boost. i'm now sitting with just over a quarter of a tank left.

The tank is 60ltrs capacity. At 125p/ltr, £40 will buy you about 32ltrs => 1/2 tank.

You say that you used about 1/2 tank for 110 motorway/A-road miles, which seems very poor to me. This is only about 17mpg! You should get around 350-400 miles for a full tank from that sort of driving, so you should be seeing about 175-200 miles from 1/2 tank.

Best thing to do is to fill it up, drive until you have about 1/4 tank left and then note the mileage/ Fill it up again and calculate the mpg from the amount of fuel you put in. Anywhere between 25-30mpg is about right, depending on your driving style and crusing/town roads.

 

[m8arx]

cheers folks, i understand the best way to calculate mpg the proper way - i suppose the mpg on the trip computer was just a guage - the real issue i have is the fact i've done 151 mile now and used half a tank and most of it was driving like a granny.

 

[emery1990]

I used in the caddy 1/2 tank in about 150miles, but got 200miles from the 3/4 to 1/2 marker.

same on my golf, top half last much longer than the bottem half.

 

[The Doctor]

I used in the caddy 1/2 tank in about 150miles, but got 200miles from the 3/4 to 1/2 marker.

same on my golf, top half last much longer than the bottem half.

Hmm, maybe the bottom half of the tank is smaller?

 

[sportstractor]

top half lasts alot longer than bottom half for me. You would of thought the clever germans would of got around this somehow.

 

[glen_jai]

I get between 350 - 380 miles before fuel light comes on.

The top half goes down slower because the when you brim your tank, I think the petrol goes above the sensor, so the gauge doesn't go down for quite some miles until the fuel level drops below the top of where the sensor starts to measure, if that makes sense.

 

[emery1990]

erm could be, but i only pit 3/4 in £40 and from that till 1/2 it went 200 miles :S then it goes down like made untill fuel light comes on and uses 150 miles in that time.

 

[m8arx]

i've now done 190 miles and i'm below a 1/4 left. if i calculate it right, thats about 320 miles to a tank (providing i get another 60 out of the last 1/4 and get 80 from the 3/4 to full mark.

 

[Prawn]

doesn't sound like a problem to me mate....

Sounds like you're also viewing the real time MPG and not the average, which makes it pretty pointless. At walking speed the engine's still using fuel to keep it running without really going anywhere fast!