have recently bough a impreza classic, when accelerating hard the engine seems to cut out at around 3500 to 5000 revs and jump really bad but you can accelerate gently through it anyone have any idea what cold be wrong?

 

Sounds like ecu is in 'limp home' mode. Do an error check and see what crops up.
See here JollyGreenMonster.co.uk

 

yeah done an error check, nothing showing, reset ECU to no avail.

read on another site it may be overboost any ideas how that would occur?

 

Overboost will typically only happen in gear 4 and 5. The first items I would check would be plugs and coilpacks. When I took delivery of my car it would jerk real bad as soon as boost came on (it had sat for about 6 months), replacing the plugs cured it.

 

How the hell is that a sympton of 'limp mode'?

Does indeed sound your hitting the fuel cut limit due to over-boost.
Is the car decatted?

 

does he not mean the car is holding back? ie spark plugs and coil packs??

 

No the car is not decatted but has got an STI back box on. other than that its fully standard, and just had a service in the last 1000 miles so sparks and coil pack are fine.

I have also taken the MAF filter off and tried another one so thats not the problem either.
I have got it booked in to have it put on the computer tomorrow so hopefully something will come to light.

How would i cure over boost?

 

Could try checking all your boost plumbing for cracks/splits, esspecially the pipe running to the wastegate, check the boost solenoid to.
Initially had boost problems on mine (under and then over) cleaned out solenoid and replaced all the boost pipes, fitted new plugs, running sweet as now for less than £100

 

Since I am new to this would you have any diagrams of the boost plumbing as I havnt got a manual for the engine yet?

 

This is a 3 port solenoid showing where the pipes should lead

Its located on the drivers side suspension turret/inner wing on mine.

What MY is yours???

 

MY97 wagon, just bought it to mess about with had one a few years ago so i thought i would buy another

 

Its my first one, am fine with n/a engines but this turbo stuff is strange, learnt a lot in the past month. When i first got mine the solenoid had been bypassed, ie the turbo nipple was connected straight to the wastegate, hence only boosting to 0.5 bar, sorted that and then wastegate pipe had a split in it, hence overboost.
Worrying at first, thorght id borght a ****ter!!!

 

had car on computer today no reported faults as i thought,
been onto subaru they said could be wastegate, or mas sensor both very expensive parts to replace, i need to know if it is this first before buying either one anyone any ideas???

just going to check over boost solenoid and pipe work now but garage said pipes look ok.

 

I would also check the intercooler pipework, especially where it connects to the throttle body.

I have had it where the rubber hose wasnt tight enough on the throttle body, result was when I floored it and gained max boost, the pipe actually pulled off the throttle body resulting in a lose of power, then when lifting of the throttle (as you do when you think you have fubarred the engine) the vacuum that had been created sucked the pipe back on so when you looked everything looked okay

 

I had this prob on my 1998 mate, took off the boost solinoid and flushed it out with brake cleaner and its been good as gold ever since.

HTH

 

cheers mate, will give that a go over the weekend, subaru are pointing me toward wastegate not operating correctly could this affect it?

 

Have you got a boost guage fitted? very cheap and helpfull thing to have, ie will tell you if it is overboost.
Best way to check the boost solenoid is to connect the 2 green connectors under the driver side dash and turn on the ignition, if it is operating correctly it will click continualy, if it doesnt then as above clean with brake cleaner. Also remove all the pipes, one at a time and blow thru them, give them a clean with brake cleaner too. Check the brass restictor is fitted in the bottom pipe of the solenoid, i can see mine, its about and inch down the pipe, should be at the end that goes to the solenoid.

You could test the wastegate by taking the pipe from the turbo nipple and conecting it straight to the wastegate actuator, should boost to 0.5 bar (7 psi) but you will need a boost guage to see the results!

 

well car is in again for more tests, but will invest in a boost gauge and do all whats been advised thanks very much for all the replies.

 

andy, i have a classic my99.. i have a dawes valve fitted, and i have turned up the boost, on a standard turbo... my car does the same, but only in 4 and 5, and it will only do it every now and then... it tends to do it when the temp outside is freezing, and is ok when the temp is 3 degrees plus...

mines a uk model, and is boosting at 17psi (approx 1.15bar) in the top 2 gears.... (AET tell me the standard turbo will take 1.2-1.25 bar of boost) like you i dont know why it does it, and as a result i will be turning the boost down to start the elimination project.. like someone previously mentioned, it could be the fuel pressure reaching its peak, in that case it could be the fuel pressure sensor which is playing up, in both yours and my case...

 

got car back from garage, redone diagnostics nothing again, turbo is running at 1.02 bar of boost.
but still no further forward so gonna get belt and tensioner done and then go for the boost gauge and look at boost solenoid and clean out pipe work, wastegate is operating correctly so am quite pleased about that.

 

Change plugs and check coil packs next then eh!!

 

found the problem was one of the actuater pipe, was lifting and dropping back down have replaced all the pipes and blew solenoid out with break cleaner and seems to be running as it should will give it a few days and see what hapens thanks for the replies.

Andy.

 

Right Posted this thread a couple of weeks ago now, thought i had solved the problem with overboost but it has returned and is as bad as ever.

Here's a list of what I have done so far

Replaced all the vacuum pipes that looked suspect.

Checked that the restictor pill is there. It is!

Checked the boost solenoid by means of the two green plugs.
that seem ok but have cleaned out with brake cleaner anyway.

I have secured the pipes as I found they were blowing off and thought this was the problem but as i have found out it this isn't the case.

Checked sparks and coils packs.

next to do is boost gauge. (saturday)

I have a couple of questions to ask and hope with some help can resolve the problem soon as its driving me mad.

1a)How do i check the actuator is working correctly.
b)Can the actutor be cleaned/lubed.

I know there are a lot of people with the similar problem and its a common fault would someone with more experience with subarus post a check list of all the parts that could be causing this or is there too many different factors that can cause this.

 

What year of car is it because different year cars have different fuel cut settings , you say you are running 1 bar of boost , which is what the fuel cut roughly was set at on mt 93 wrx , standard on mine boost was running at .8 bar 12.5 psi so if i turned the boost up it would hit the fuel cut limit set in the ecu as fuel cut was 1 bar ,bought a scooby ecu chip which raised the boost to 1.1 bar and raised the fuel cut to about 1.25 bar , i still think you are hitting the fuel cut limit set in the ecu .

Mark

 

IIRC the fuel cut on MY93 is 1.02 bar so could easily be hitting fuel cut, your standard boost is 0.9 i think

 

It is a MY97 uk turbo

 

BTTT

Have fitted boost gauge and when its cutting out its over 20 psi and holding at around 17psi when driving normally

 

Still does sound like fuel cut seems to be running to much boost for standard and with spikes over 20 psi it will be hitting fuel cut what has been done to increase the boost ?

Mark

 

I had an identical prob ,I bypassed the soleniod with a dawes device, lowered the boost to 15 psi and hey presto Perfect
Def hitting the fuel cut on mine sounds the same for yours

If you car is running the std ecu 17 psi + is too much

 

As far as i am aware the car is standard other than wheels and back box, but by what i have been reading here and seeing what its boosting at im a little worried as i know its to high.

all hardware seems fine

could it have been chipped, where is the ecu and would i be able to check it myself??? any pictures of a standard ecu would be welcomed or a chipped one so as to compare mine and advice as to where its location is.

Been reading a bit about dawes systems how much to fit one and would this enable me to reduce the boost to what it should be without any ill effects on the engine??? or can i reduce the boost without one? other than this problem the car is fine.....so its annoying me a bit but i will not be beaten lol.

another question, Is there a difference with the my96 and my97 models as mine was first registered in jan 97 would this model have the td04 or td05 turbo?

excuse my vague knowlege but this site is helping immensly.