Pete Croney

My money is also on the emissions algorithm in the ECU.

Here's how it works...

To get the car through new vehicle type approval, it has to be noise tested under full acceleration between two points. Turbo cars are notoriously "noisy" when on boost.

What Subaru (and lots of other manufacturers) have done is write a routine in so that if you hold a steady throttle for longer than X seconds at a speed of between Y and Z... and then nail it... you only get half boost.

The car passes the noise test, everyone is happy. Except you, when you replicate the test conditions and pull out expecting full boost.

Give the throttle two prods if you've been steady at between 2500 and 4000 rpm for any period of time and normal service will be resumed every time

Once you know that the car has this routine, you can replicate the test every time you try.

SiPie

Thanks very much Pete

Mike Nolan

I've had this on my MY98 WRX wagon. Found the following article in the SIDC FAQ about oil levels and the boost solenoid. Mine only started to hit the fuel cut within 2 weeks of having a service, and it had been filled right up to max.

-----------------------------
3.2 Waste gate solenoid
The 1997 specification lowered the turbo boost pressure from 1.0 bar to 0.9 bar. The engine breather system vents into the air intake and it is possible for the oil and condensing, burnt oil vapours build up in this valve. This valve is a safety device for detecting overboost and will cause fuel and ignition to be cut if it senses that 1.2bar (97/98 models) has been reached. If it is bunged up, it isn't sensing correctly and will shut down the engine under high boost conditions. The solution advised by Subaru France was not to fill the oil up to maximum but to leave it at half filled only.

If your wastegate solenoid does pack up, the fix is to pull the T shaped supply hose off and fill it with brake cleaner from an aerosol. Then go for a blast before the cleaner evaporates. Tippex thinners also do the job. '98 models have a revised part, which is three port sensing and there have been no reported failures. You can get '97 cars upgraded.

Apparently the fault often occurs just after a service when the oil level may be slightly too high. The 1998 specification engine apparently has revised sensing locations, to over come the above problems but there have been some reports of failure on early '98s.

Sometimes this fault is incorrectly termed as "over boosting". The sensor is designed to detect an over boost situation and is usually so sensitive in normal operation that 1.19bar = ok and 1.20bar = fuel cut routine due to over boost. When it becomes contaminated by oil, this is lost and the sensor can cut in at much lower boost values, cutting in the routine under normal hard acceleration. The effect of this routine is quite disconcerting as all engine power is suddenly lost with some drivers reporting it feeling as if they have just driven into a brick wall!
---------------------

Mine cured itself during a 4000 mile drive around France after Le Mans this year.

Apologies to SIDC for copying this text, but as it is on the public part of the site and it may help a Scooby owner I am sure they would not mind.

Mike

SiPie

Yeh I too read that Mike...thanks, and I hope it helps some other owners.

Mine's a my99 however

Cheers

john banks

We could ask Stephen Done to look at the ECU code and try to disable it, but he is busy working on the MY01 at present. I'll mail him.

You could fit a Dawes and it won't happen, but I would rather live with the JECS boost control for the benefits it gives.

SiPie

Sometimes it's a shame you can't change the title of a thread...!!

Poor Optimax getting a slating huh???

Bob Rawle

Steve can't get at that code at the moment and he is pretty busy. For the emmissions thing to cut in you have to hold the car in second gear at about 50 mph for several seconds, then it limits to about 0.5 bar boost but it still goes, certianly enough to overtake, what has been described sounds nothing like this.

The cut and paste from SIDC is not accurate either and somewhat misleading, there is no specific sensor for boost cut and the solenoid and map sensor are both just part of the overall boost control circuit. MY97 and 98 UK cars both have two port solenoids, STi4 has three port only, all other of those years have two port (actually not sure if MY98 WRX had three or two port).

I still think its boost cut, if it occurs and you don't get out of the throttle straightaway then its as described.

sKunk

Had this happen to me but with 95ron unleaded. I don't think it's the fuel at fault.

ustolemyname??stevieturbo

iTrader: (1)

Well if someone suspects a garage is selling dodgy fuel, branded as optimax, then surely trading standards could be called to investigate. Isnt it illegal for them to advertise as "xxx" when it may seem like it isnt. After all it could potentially cause enginge destruction. Im sure that even if they phoned the main distributor, to ask if the particular petrol station has even been delivered any optimax in the last few weeks, should give an idea if its the real stuff.

MRK

Well after reading this the other day i went out for my sunny lunchtime blat, and tried out Pete's recommendation.

And in fact the car does it ‘everytime’ .

If I hold the revs constant in 2nd between 3200rpm and 3900rpm for a minimum of 3seconds then I’m restricted to half boost

I couldn’t get the ecu to stop this by blipping the throttle twice though.

Now I’m aware of it, the very fews times I ever need 2nd for overtaking, I’ll just alter my revs when waiting to blat pass.


M

SiPie

MRK...

Is it an MY99 you have or is this common to all..?

Interesting to hear that you can get this to happen all the time

Cheers

Jza

Ive been using NUL - i get 1.2 bar boost at full pelt.

I filled up with Optimax.. 1.3 bar boost at full pelt.

Is this why people find boost spiking?

Jza

Mungo

Have also experienced this twice. UK MY99 using Optimax. I've always thought it was related to fuel starvation as the tank was below 1/4 full on both occasions.

Krade

Ive read most of the thread and it seems similar to something I had a few times, I was just blasting up a A road from a standing start and after changing to third gear the car seem to hit the revlimiter at about 60-65mph or 5k revs, being inexperinced with Scoobys I wasnt to sure what it was but I guess it must be over boost.

SiPie

Have since heard another 'theory' on this one.....!

Here goes.....

Apparently the higher Ron of Optimax may make the turbo spool up slightly quicker and the ECU therefore doesn't quite have a chance to 'catch up'..on occasion under hard accelaration!

Personally I think this is complete bollox but seeing as I know very little about such things thought I'd leave it to other peeps to shoot down....?????

pslewis

Hmmmmmm I work in Electronics and I have yet to meet an ECU that cant keep up with a mechanical device!! Switch the light on and see how fast the electrons hit the lightbulb!!

I havent a clue why it happens by the way - just wanted to end any stupid idea that the electronic brain 'struggles' to keep up or catch a mechanical turbine spinning as fast as it possibly can!!

Pete

kevin stanton

here's one for you all.

I've got a MY99 UK turbo with the standard ECU.
I use optimax and millers octane booster all the time and have done for nearly a year.

No problems what so ever. Smooth acceration all the time with no jerks or lumps.

Kevin

Flat 4x4

Kevin Stanton

I also have to 'admit' that I've seen no problems with my 99MY with Tek2 and Optimax over about 7000m.

Do you find the Millers booster makes a difference - ie have you tried it without ? - very interested to know as I thought it would only make a difference on import models. Recommend it ?

SiPie

Don't worry... was just airing another of the many and 'varied opinions' I've now heard on this one.....

I'm sure it's down to the emissions thing (especially since people have been able to replicate it by holding revs between 3250 and 4k in 2nd)

Still well dodgy whatever the cause!

Sheepsplitter

So if these 'boost problems' are occuring because of the higher RON content of Optimax (98.7 I believe), what do the Japanese market STIs using 100RON fuel run like?
Are people suggesting that in Japan you have to drive expecting boost cut problems ALL the time?

SiPie

Sheepsplitter..

Think we are all agreed that the original advice from the dealer was bollox (surprise,surprise) and it's simply down to the ECU thinking it's being emission tested. No problem with the fuel etc...

Cheers

Bob Rawle

Since the electronic brain can only do what its allowed to do then if its constrained by settings to work with "normal" fuel conditions then the extra aggression that is Optimax could well mean it can't "keep up".

Bob

johnfelstead

As usual Pete, when it comes to mechanics, you are talking out of your ****! LOL

The Boost is controlled by the ECU via a solonoid that controls airflow to the turbo waste gate actuator. If the Turbo spool up speed increases, the ECU map wont be able to affect enough of a change quickly enough in the solonoid to control the boost spike. You can get around this in two ways, one way is to change the ECU map to cater for the faster spool up (ie an electronic change in the system), the other is to change the amount of air available to the solonoid by increasing the size of the restrictor in the waste gate supply feed pipe.

This is hardly new thinking. you can get boost spikes for lots of diferent reasons, such as fitting higher flow up pipes/down pipes, more eficient turbos, more eficient fuel etc. Sometimes you cant control boost spikes until you install external waste gates, such as used on the Focus WRC engine which has a very fast spooling turbo.

Hope that educates you a little m8.

johnfelstead

BTT for mr anti gold wheels.