Before we start, I know fuel economy and STI’s don’t go together but after comparing others averaging 17-22 mpg, to mine which can return a bit less there must be something wrong (and believe me, its not down to a lead right foot!)
Its not changed in any way, it’s always been like this and I’ve been living with it. Only realised something was wrong when out on a run with fellow STI PPP owners that mine needed filling up way way before them, which led me to do proper mpg calcs.



It’s a 03 STI with PPP fitted from new and no extra mods and the car runs fine.

I’ve had the car at two Subaru specialists. Firstly checking the ecu via laptop and the cars power via a rolling road – all ok.
Secondly its been checked out with a Subaru select monitor, all the readings taken and compared with an identical STI PPP sat next to it and everything is just about identical.

 

I would say I only average 15-18 mpg, My driving is mostly on country roads where you are always on and off the throttle, On a run to Leeds last year up the A/M1 it returned an incredible 23mpg, Hope this helps a little!

 

if thats town roads etc then thats same as i was getting on my 05 sti ppp but on motorway goes to as above 23+

 

I don't think there is any real logic to it. On old fashioned optimax I could get 30-33mph in my '03 wrx. It now has vf35 and sti injectors but even before that it started to return around 22-25 mpg on V Power which is part of the reason I thought sod it lets upgrade. A while ago I actually got 400 miles out of a tank crawling to Norfolk and back. The same car would no way do that now. Go figure! Remap might help. PPP is a bit one map fits all.

 

the rear o2 sensor is there now to check the state of the catalyst it's the air fuel ratio sensor you want to be looking at

 

Thanks for the replies.
Regarding the mpg N*UFO and Swifty I would accept 15-18 for a blast and be more than happy with 23+

Mgcvk – A re-map is a possibility but I don’t want to get into re-mapping when there may be a sensor or something not right in the first place.



Scoobyboy - Where exactly is the air fuel ratio sensor located and is it known as anything else?

.

 

check your tyre pressure's and compound's. they can have a big effect on MPG.

also things like brakes, are they binding? what oil you have, when did you change the oil?

little things make a big difference

also do you use the aircon?

 

Thanks carbon. I would say everything above is ok. Tyres and pressures regularly checked, brake fluid and pads all changed and no problems, Serviced at dealers so the recommended Shell Oil used– 40K service recently done and no change after that.
As for using the aircon – no chance, dont use that!

 

In all honesty, 15-18mpg is all I get driving quite placidly on the roads around here!, On a blast it's around 10!, When I got the magic 23mpg figure I actually set out to see what mpg I could achieve, Really was driving like miss daisy! it was a steady 65-70mph on dual/motorway for nearly 200 miles, maybe mines a bit thirsty too, Will be when I get my 2.5 fitted! lol

 

I get around 23mpg and am running around 380-400bhp on my newage.

I would be disgusted if i got 12-17mpg, never got under 20mpg and returned around 26mpg on a long run

 

I live on the isle of wight and all the stop starts and short journeys mean i get on average only 200 miles out of a tank.

And thats mostly driving off boost when ever i can!

On the mainland thats nearer 240 miles a tank easily..

 

the air fuel ratio sensor or ayf as it's known at dealerships is the one on the corner at the front just before the uppipe the o2 sensor is the one about halfway down the car, what were it's readings?

 

Your car has been remapped, we are talking standard PPP cars, The map is crap!

 

220 standard 50l optimax
275 current 50l vpower & NF

392bhp

 

scoobyboy - I did a search on AYF and came back with the thread you posted on, talking with Bob Rawle.

I hope some of these readings from the Select monitor are the relevant ones for you – I’m not sure what they mean!
Taken on tick-over, when warm after a 2 mile run.

AF Learning : -3.9%
MAF: 3.06

AF Sensor #1 resistance : 26 ohm
AF Sensor # : 1.00
AF correction #3 : + 4.92%


Just to clarify – I presume I’ll need to work from the underneath of the car to see where this AYF is located, looking up at the front set of headers? I’ll get out for a look a bit later on today

Just one extra thing that may be relevant to you: the “Rich signal O2 rear” was flicking between On/Off but mostly was showing On.

 

Ok found the AYF sensor (I hope!):



It will be changed this weekend for one on approval to see if it makes any difference.


Thanks for the replies everyone, especially the tech support from scoobyboy.
Will keep you posted as to what happens and I’ll be back for more ideas if this doesn’t solve it Cheers Carl.

 

The Air Fuel Ratio sensor has now been changed.
MAF changed.
ECU reset.



At the weekend on a 160 mile motorway run it gave 24MPG which I’m very happy about and probably in line with others, but when you start to use the car properly it can still use less.

 

It's not right. My My03 PPP did 25 usually (country lanes) 28-30 motorways and that is with a fairly heavy right foot. The brakes could do this, you say all changed but it might be worth just jacking up each wheel to give it a spin. My GTE got me this may many moons ago.

 

I also had problems with my STi 05 +PPP using loads of fuel. A local Subaru garage (not the dealership I bought the car from - they are a useless lot) noticed a slight smell of fuel when doing some work under the bonnet for me and found that the fuel tank gasket had been damaged when the PPP fuel pump was installed. They kindly replaced it under warranty. I also had a remap the week after, so am not able to say exactly how much difference the replaced gasket made on it's own ... but since then my car has had about 30% better fuel economy.

Check the gasket first, if that is OK, then I would say a remap would be your next best option.

Hope it helps.

 

MY03 STi only gives about 160-180 miles to a tank normal everyday driving, alot less if I open it up. I have had 230 miles on a long run driving at 80mph off boost in 6th.
I think you will find its about right
Still better than my wifes Disco 4.4 which does about 7-16 mpg if you are lucky.

 

Thanks again. Had heard about the gasket problems before, never smelt fuel but will check it out all the same. Brakes definitely ok.

scoobystiv8 – Your figures sound similar to mine.

 

Hey Carl,

No matter how I drive mine I always get 220 miles from a tank of fuel. That was with the PPP and now with the TSL map. I suspect this is down to the A-roads and country lanes I have to use to get to work and back. Once on a motorway if I can keep my right foot under control I do see a lot more mileage from it.

Just one of those things have to put up with I think.