I have been told that running a scooby (1996 UK model) on super (97 octane) will increase the power output over normal 95 octane unleaded. This makes sense.

To get this extra power I have been told that the ECU will automatically re-map itself to the higher octane fuel ( I assume by use of the knock sensor and advancing the ignition as far as possible). Is it best to just drive it and let the ECU re-map itself or would it be better to disconnect the battery over night (the ECU will loose the mapping as the Subaru garage told me) and start a fresh.

Also, if I were to use an octane booster additive, how far will the ECU go i.e would it map up to 100 octane fuel for example.

Some say do the reset (by disconnecting battery etc) and others say it has no effect. I reckon the ECU is intelligent enough to learn what's going on and adapt reasonably quickly without having to be brainwashed by the reset, but you can speed the process. This worked for me: fill up with super, make sure the engine's fully warmed up, go to your local dual carriageway / motorway, stick it in 5th gear, then give it full throttle on a flat or slightly uphill bit from about 2250rpm to around 3750rpm, then lift off. Do this about three times (ideally between roundabouts if you can). This lets the ECU learn what fuel it's getting, knock points etc under full load, and it adjusts its parameters accordingly.

My car was noticeably quicker in the gears after this process (timed by stopwatch) -- as an example, 40-60 in 4th went down by 0.3 seconds average over several runs.

Thanks for the info. I have been canning it for the last few days, foot flat on the floor pretty much right from idle to the rev limiter so it should be remapping itself. I think I can notice a difference.

Have you seen a reduction in fuel consumption since using super?

I switched to SUL about 5 tanks ago, did an ECU reset after 3, I have seen no difference in fuel consumption, and am still trying to convince myself of any increase in power/smoothness.

Stuart

Kaning the car, foot to the floor is exactly the WRONG way to set maximum paramters for your newly reset ecu guys.

Sunil

Sunil

OK, so how do you set the maximum parameters of the ecu? since driving it hard after disconnecting the battery for a night is what the Subaru garage suggested I did.

[This message has been edited by Spatch (edited 10 December 2000).]

Sunil, if you don't floor it, how is the ECU supposed to know optimum settings for flat out driving?

Prodrive have assured me that the ECU learns its new optimum parameters very quickly, ie as soon as the engine encounters new circumstances, corrections are made.

I have a method of resetting the ECU (MY00 UK) after a fuel change which involves running the engine through a set of circumstances similar to those recommended on the SIDC site. Flat out through the gears and in particular, flat out from 1,000 to 7,000 in third (LOTS of left foot brake!).

Don't tell me that it doesn't work as I've done it several times and the stop watch doesn't lie.

Hoppy

I was told to disconnect the battery for a couple of hours, then start the engine and leave it to idle for at least 15 mins, then re-start the engine and bob's your uncle...

Can't remember who told me that.

Stuart

The newer ECUs (MY99 and MY00) are able to adjust to different fuel more quickly than older models. The best way to reset the ECU quickly is use the MRT rally method (web site often quoted but I can't remember exactly).

This is how to do it (sounds dodgy but believe me, its very easy):

1. engine should be warmed up.
2. switch off engine.
3. connect 1 black male-female and 1 green male-female connector together (these are the Check Engine and Select Monitor connectors I think). In my car (MY98) these are found just beneath the steering column shroud alongside the ignition.
4. switch on the ignition but don't start the engine (you will then hear the cooling fan go on and off and lots of worrying relay clicking - this is all normal).
5. depress the accelerator fully for a few seconds and release.
6. start the engine.
7. the check engine light will flash.
8. drive for more than one minute at more than 10 mph.
9. ecu now reset.
10. disconnect the 2 connectors.

The ECU now has to re-learn. My understanding is that you should drive for 20 or more miles using a mixed style (both gentle and more aggressive). Ideally your tank should be full of SUL (plus or minus octane booster) if you want to notice any difference.
The main difference I noticed was economy rather than an improvement in outright performance.

D.

Hoppy, i am not going to lie to you - you just carry on.......

Have fun

Sunil http://bbs.scoobynet.co.uk/smile.gif

Blimey - dont think i want to get involved with this one....i lied

IMHO. MY99 UK car almost std spec
I struggle to find Super unleaded before i am about to run out - Bad planning and all that.

I ran my can on unleaded then tried SUL. i think it took about two tankfuls to reset the ECU to the higher rating. after that my car ticked over more smoothly, and seemed slightly more responsive, it also seemed to be doing about anothe 20 or so miles per tankful.

I think i shal try octane booster and run mine on standard unleaded.

I've just changed to SUL as my car kept missing and being unresponsive on BP UL, which was bought from different garages.
First tried Texaco SUL as nearest, then Shell as cheapest, then on the North Wales meet Esso.
The car is now much smoother and seems more responsive. Consumption seems to be on a par with UL.
I shall stick with the SUL, and am going to try some octane booster next.

Jon ( MY99 )

DJB,

Thanks for that, although I am a bit reluctant to start connecting wires together in case something goes phut! especially as mine is a bit older than yours and the wires might not be the same!

You say that the older units take a bit longer to re-adjust to SUL, have you a ball park figure for this as Paul H said that his '99 model re-set in two tankfuls. I am only on my 2nd tank.

I am also assuming that the ECU will fully re-adjust just by driving on SUL rather than using other methods - the only difference being that it may take a little longer.

hmmmm...

Spatch,

Pete Croney instructed me to drive the car on full load for about 9 seconds (after he reset the ECU). This seemed to work fine (STi V).

Sunil,

as ever, you seem to know best, so why don't you tell us? http://bbs.scoobynet.co.uk/confused.gif

Dave

I used to reset the ecu on my my99 every month. Use the under dash connector method and ran the car up a long hill with high boost between 4 & 5k rpm.

Gave excellent results - obviously, 'cos I kept doing it. But I *think* it was noticeable 'cos I drove the car like a woos part of the time (through built up areas).

Going to try it on my PPP'ed my00 soon.....just as soon as I get used to the current performace http://bbs.scoobynet.co.uk/biggrin.gif

Richard

Just following on from what Schuey was saying about fuel from different companies. I am on about my 5th tank of SUL now and I have found ESSO to be the best so far. I put a load in from TOTAL and it felt less responsive, slower, just generally pants.

I was quite surprised at the difference from supposedly fuel made to the same British/ISO standards.

[This message has been edited by Spatch (edited 17 December 2000).]

Spatch, from your fantastically unscientific experiments, are you suggesting we all now avoid Total fuel?

C'mon guys, posts on this board deserve at least some objectivity.

Hoppy

OK, I'll throw a few cats amongst the pigeons....

I did loads of research on this 6 months ago, searching the archives of this bbs and other sites and in my little mind believe...

There seems to be 3 different types of ECU, each reacting differently to fuel.

The earliest type just adjusts down, so it will map for the lowest grade fuel its seen, not adjusting up when better spec fuel goes in.

The next one adjusts up and down, but takes an average of all the fuel in its memory, hence the rough batch of fuel it saw a few tanks ago can still have an effect on settings.

The latest ECU adjusts up and down, optimizing settings and regularly updating its memory - hence 'forgetting' about that rough batch of fuel a few tanks ago.

Now I don't claim to be an authority on this (and would welcome comments from someone who is http://bbs.scoobynet.co.uk/smile.gif) and I don't know which model years had which ECU but I would say that IMHO I'd reset the ECU if I didn't have the latest spec type.

Oh and use the MRT method as mentioned earlier http://bbs.scoobynet.co.uk/smile.gif

Hope this helps in some way...

Justin

I've got a UK 96 same as yourself Spatch, and used the MRT reset method, following exact insturctions as on there website.
After the reset the MPG was definately better, the engine run a lot smoother and better idle with smoother acceleration. Power wise I didn't notice anything much at all.
I've done this same reset before, the last one after I'd been using super for a while. Straight after the reset the car felt sluggish and non responsive, after a hard run it was back to it's normal (super) self.

Just my opinion based on my experiences http://bbs.scoobynet.co.uk/smile.gif

Darren.

Sorry Hoppy,

I should have qualified my subjective opinion as 'based on my own experiences'.

But fuels CAN vary between manufacturers and batches.

[This message has been edited by Spatch (edited 19 December 2000).]

Spatch, no probs http://bbs.scoobynet.co.uk/smile.gif

Hoppy

Milky (Darren)

You say that you reset your ECU using the MRT method. Did you do the same as described by DJB above, since he is refering to a later car? (wires could be different?)

With M MY00 new in September, I notive a difference in UL to SUL within half a tank first it idles and pulls cleaner, than after about 1 more full tank theres more response and maybe more power, that's what it feels like anyway, I also seem to get another 30miles out of a tank of SUL to UL.

Spatch

The method I described above is copied from the MRT rally website.

They state that the location of the connectors varies with model but I think that the basic method is the same for all models. Find the four connectors (2 green male/female and 2 black male/female). On my car there was no doubt that these were the right connectors since there weren't any others in the described location. I was wary about the ECU reset first time but when you see the connectors, its clear what to do.

D.

The MY99 onwards ecu's dynamically (quote "constantly") adjust to conditions and they are "constantly" looking for optimum so whatever the fuel etc the ecu is very quick to accomodate. The reset is not needed on these cars. Earlier cars have ecu's which will adjust down quickly but take much much longer to adust back and sometimes don't at all, for these the ecu reset works but caning it straight afterwards is very likely to undo the reset. You should drive in mixed conditions for 25 to 30 miles allowing the engine to briefly boost up twoards max, by the end of this the ecu will have adjusted itself and will stand a far better chance of staying more advanced etc. If you just blast it then there is a more than even chance that it will sverely back the ecu off and, if the ecu was already backed down to minimum, it will cause the engine to suffer detonation etc as it will have reset itself to 100 ron fuel in the case of the Japanese import.
So some common sense is needed depending on why the reset is being carried out, if you are moving up in fuel grade or adding booster then benefit should be seen, if there is none then the engine was at max already. If you are trying to solve a problem then you could well be making the engine suffer more.

Bob

Important Notice. For those new to this board and therefore (temporally) unable to conduct a search on the popular yet mystical subject of resetting the ECU, it is vital to know that Bob (above post) is an engine management God. Just read and believe - it saves an awful lot of time and argument!

Hoppy

PS It appears that from MY99 UK onwards, there are significant changes to the Impreza in a number of key areas, ECU, brakes, suspension to name just three. It pains me to say this but: apologies Sunil. You may be half right after all!

[This message has been edited by Hoppy (edited 22 December 2000).]