Is anyone else suffering from overboost? I've had a update fitted but it dosen't work. The garage hasn't got a clue how to fix it.

From all the posts on this subject I think a lot of people suffer from this problem, to a lesser or greater degree.

I have had the problem from new but I don't think it is bad enough to bother about. I only get it in 5th between about 70 and 80 at half throttle and above.

There seems to be a few things which can cause the problem including plugs, solenoids and restrictors. If it is giving you major problems then I suggest you persist with your dealer or try another one.

Mick

I've just had mine fixed (for a 2nd time). The problem is that the overboost sensor gets contaminated by oil surging. Subaru tried a 3 way sensor but this didn't fix the problem so they've gone back to a 2 way. The sensor is located on the left hand side of the engine bay just above the air filter and is about 3 inches long and has two black rubber hoses going into it. The oil surges up the pipes and either contaminates the sensor or restricts the pipe width so that the sensor registers incorrect pressure. This usually happens when the engine is on full boost, i.e., 3rd / 4th gear 4000rpm and you get a sudden thud as your engine shuts down (briefly - it's doing what its told) and you feel like you've hit a brick wall. Once the sensor is contaminated you'll need a new one and it will be replaced under warrenty and is a 5 minute job. You can also try the following;

Stick your head up underneath the dash board and find two cables with green connectors on them. Join the two together and switch on the ignition (not the engine). This will cause the solenoid to flush the pipes. You can hear this happening by the solenoid ticking on and off (make sure you're air fan is not on or you won't hear it). This should cure the problem in the short term.

Hope this helps

cheers

ANdy

Just to confirm what andymac is saying. Most of the time it's caused by overfilling the oil. Doing the 'wires under the dash' trick will clear the pipes. But if your oil is still overfilled then it will come back again. Even after taking some oil out chances are you'll still need to replace the solenoid as it'll be beyond salvation.

So

1) Get some oil taken out
2) Try the wire trick (see if it comes back in the next couple of days)
3) If it comes back - then get the solenoid replaced (under warranty)

Link to the wire trick is here

I may be stupid. But what is overboost and what are the symtoms????

I went back to the garage for the fourth time today, and touch wood, all is well until now. One of the tubes had a very rough inner surface and after replacement cured the problem. (For now)

The mechanic said that more than half of the cars have the Overboost problem in varying degrees of persistance. One guy got a brand new car for a "nominal" fee, after having spent 5 months trying to fix his car. Even the technical specialist from Japan did not have any ideas.

It seems that there is no single cause for overboost and that the system itself is very vulnerable to contamination, split or porous pipes, high oil level, bad quality tubing etc. etc. etc.

I really don't think it is acceptable to have your car overboost at all even if it is only in fifth gear. Having said that, it's not easy to fix. Good luck everybody.

Andy mac

the bit of kit you are describing is the boost control solenoid.This does not sense anything and is just a control valve.The sensor is mounted nearby and only has one pipe connected to it.

The oil does coat the solenoid and the restrictor this prevents the solenoid from controlling the boost at the correct level so the boost rises too high and the ecu cuts the ignition.

Once the solenoid is contaminated a new one is NOT required,if your dealer replaces it its a sure sign they don't know what they are doing.The solenoid is easy to clean and then works like new again.

Connecting the green wires under the dash does not clean the solenoid it just pulses it open and closed(This is the ticking noise you can hear).When the engine is running the solenoid is pulsed continuously anyway.

A thorough clean of the pipework,restrictor and solenoid should cure the problem

check out

I have just had the complete sonenoid replaced under warranty. Now no boost probs, YET!!!!

Dan

Hi AndyMc
Thanks for the additional info - I was just relaying on what I was told - Mechanics eh ?! I had just had the car serviced (cam belt thing at 45K and this was the first time it had been to this dealer). Previously I had had a 3 port solenoid fitted (after it had done it before). I'm now back to the 2 port. How does the oil misting prevent the solenoid from working / causing the actual sensor to stop working properly ?
What's this about an oil/mist catch tank thingy as well - easy to fit ?

cheers
Andy
(Wanting to solve this problem once and for all before my warrenty runs out...)

When I had the problem a couple of months ago (on 40,000 mile 97MY), my dealer fitted a "boost restrictor". It solved the problem, although the car does feel a bit slower now.

What are my chances of getting the root of the problem solved by my dealer, and getting this restrictor out? I've never really understood what the restrictor actually does though.

Cheers,

Stephen

Or you could do what I did to solve the problem once and for all without losing performance and no more probs...ever.

That is to replace the crap boost control solenoid fitted as standard with a much better and more sophisticated HKS EVC4 boost controller. I gave up after my car came back with a restrictor which seriously limited performance in the first three gears.

I now run 1.15bar of boost, the Impreza overboost cuts in at approximately 1.2bar on the standard setup. My car was trying to run at 1.35!!! After having a restrictor fitted it was lucky to see 0.9bar. The unit works perfectly, has restored full performance and some, and doubles as a boost gauge and is adjustable so you can set boost to what you like, not advisable to go over 1.2 on UK cars!!

Hope this helps,
Nito

Nito - go on then,

- how much?
- where from?
- how easy to fit/who did it for you?

Ta!