After fitting a de-cat zorst my MY00 Impreza has started to use alot more fuel.

The first tank of Optimax I put in before the exhaust got me just under 300 miles. After the exhuast was fitted I'm unlikely to get 260 out of it at best.

Seems quite a bit to me. I put it down to me booting it a bit more to listen to the sound but having driven very gently over the last few days it still seems to be drinking it.

I'm not that bothered as I don't do too many miles per week but its put me off doing any more mods to lose even more mpg. I was planning induction, ECU, better fueling etc but not if I'm chained to the Shell garage.

Any advice appreciated.

 

I went decat around a month ago, and my mpg has gone downhill considerably.

Although i do a lot of town driving, which doesn't help.

I'm hoping a remap (which will be happening soon) will help things out a little.

 

What you'll most likely find is that the 'pottering about' economy should be better after a decat as the car will be running considerably more efficiently. However... it's far easier to use more fuel than before for the same reason! Ie, if you were to somehow manage to find a way of running your car at a steady 70 (ha!), the mpg would be better than before(decat, more efficient flow). But the moment you accelerate, the car is able to 'process' more air (decat, more flow) so more fuel is also used...
I think you'll find it'll even out once you 'stop playing' and adjust to the different boost point, etc. I can get 34mpg on a dull journey & am running around 400bhp, so it's quite possible; it's also remarkably easy to get that to, ahem, 'dip' to around 18mpg

 

Now you say that it sort of rings true as whats going on.

I filled the car right up to the max or as much as would go in before I chickened out without it spitting back out at me and a 70 mile trip at farting about speeds say 50 to 70 seemed to hardly move the needle.

I mostly do town driving which does seem down on mpg than before but there are a few by-passes in the area and this is where those "Short squirts" are really costing me. One quick blat over only a mile and the needle moved quite considerably.

If I go for the group-buy TEK2 will that improve fuel efficiency?

 

Maybe there is something wromg with my car then because the best I have ever managed in a tank was 220 miles (UKMY99 Turbo). Made no difference by changing the back box to scoobysport and decatting the centre pipe (straight through).

But it does drink more when you are driving with windows down to hear it because the foot sinks deeper into the carpet for that to happen!

 

I think my drivers window is somehow attached to the accelerator as when I put the window down the car goes faster and when I look down my foot is flat to the floor wierd

Darren

 

Crappy economy is likely to be because your lambda is knackered - they only last 30k & should really be changed then, but they aren't down on the 'list' as a consumable, and so aren't.
When they are on their way out, they read lean, which means the stoich point (at a cruise) will be moved to a richer mixture, ie the ECU is overfuelling. This won't show up on a LambdaLink, etc. as typically this will be displaying the same info the ECU is basing it's calcs on, i.e. is erroneous too

 

Busted Lambda? That doesn't sound too good. How else can I tell if theres a problem with the Lambda sensor?

The car idles fine when hot and doesn't seem any different driving-wise other than a bit more eager since the exhaust was fitted. I've done a search and it seems these sensors vary in price from £30 to £120

I guess if I'm planning a re-map in the new year I should sort this sort of thing out first.

 

Idling will typically be fine with a dodgy lambda - until it gets to a silly level, the engine doesn't mind idling rich at all!
Aside from seeing what the voltage readout is from the lambda under acceleration (compared to the MAF, assuming the MAF is in good working order), I'm too sure of any 'checks' that can be done! If you do have an AFR guage, if the mixture gets apparently weaker more easily under hard use, then this is a sign as well (the lambda will typically underread more easily when it gets hot).
If you have done more than 30k on the lambda, it's time to change it. It'll pay for itself in fuel saved fairly quickly anyway!

 

crikes!! are u saying that my 98 impreza at 54k miles needs a new lambda sensor

if symptoms are low mpg, am getting around 220 off a tank without over thrashing it!!
also its idling at about 700rpm...is this about right?

[Edited by smb1 - 11/26/2003 3:41:39 PM]

 

May well be, yes. Some are made better than others (like wideband ones - the actual sensor can be £200 for these, though ) can last 100k, but IMHO it's well worth having an accurately-reading lambda sensor as possible! Especially if you do a lot of miles

 

Mines only done 25k although its on a 99 V. So I need a Lambda sensor and a new MAF??!!

Are the updated MAF's better than the originals - ie are they more hardy?

I honestly average between 145 and 200 miles to a tank. Even cruising the car is cr@p on fuel...

 

Well, it looks like I'm only going to get 200 miles out of this tank so perhaps the Lambda might need replacing. Do I really have to pay £200 for a new sensor could it have been damaged when the exhaust was fitted?

If it isn't going to damage the car I might try another tankful and be very gentle and see whats happens.

Was hoping for some extra gauges and a re-map for chrimble

****!

 

A normal lambda should be, I think, around £70 from a dealer. There are other types that can work (generic ones) but may well require some piddling about with a soldering iron to get the fittings working.

The 'new' MAFs are much hardier, yes - a good buy IMHO, even if there's nothing wrong with the current one (yet)!

 

Any idea on costs for the MAF for a MY00? I'm getting a K&N next week and I know induction kits can kill the MAF on the MY00 so may as well get one too.

You get yourself all fired up for mods and then tedious little things like this come along.

bugger.

 

Around £76 from a Subaru dealer. Part number is 22794AA010

If you're worried about that, get a panel filter. TBH there's sod all performance difference between a good panel and a cone nowadays.

As far as the lambda sensor is concerned, you can get the Halfords L300 universal one for around £30, and sort the plug out yourself, or get one from these people for around £45 ready to fit.

As a general rule, it's better to get the car working the way it's supposed to before you start changing stuff.

[Edited by greasemonkey - 11/26/2003 11:52:23 PM]

 

Nice one GM, as I'm not sure if I've just been booting it too much or the car does have a fault I'll get a Lambda from cat-direct. One final point tho, having done a search am I right in saying I need the 3 wire sensor? I've a UK MY00 and she will fit straight on? don't fancy waving a soldering iron around under the bonnet

 

And another!

A friend has suggested resetting the ECU to see if that helps. I've done another search and know how its done but not entirely sure I want to go jabbing the cars electronics with bits of wire.

Also, if my car is MY00 some posts suggest it should adapt by itself? Also, I guess I'm in danger of it giving me fault codes I'm not expecting.

 

Indeed it is a 3 wire lambda. But I still had to crimp the OEM plug onto the end of the lambda wires. Mine was a universal one though, not from Greasemonkey's second suggestion.

Resetting the ECU isn't gonna knacker your electrics...! And yes, it might throw an unexpected error code, but better that than burying your head in the sand, isn't it? You're right in saying the ECU adapts itself, but that can be both good and bad. Good in the sense of adapting to different quality fuels. Bad in the sense of learning to get round a slightly faulty MAF. It's probably worth resetting it just to test if your MAF's OK.

 

Use the "search facility" there are thousands of posts on this which wll answer all your questions.

MB

 

So is the universal Halfords Lambda any good then???