View Full Version : Overboost problem again

18th June 2000, 09:53
Car is MY97
About 12 months ago I started getting the dreaded overboost cutout problem. After numerous trips to the dealer we finally sorted this problem to my satisfaction(once the car came back with about 30hp down! and others with the overboost still there). A couple of weeks ago the problem reoccured !
Another trip to the dealer to fit yet another revised restrictor. Guees what, today the overboost is back.
Some questions I can't get my head around, maybe somebody could help please.
Why has the car been o.k for 12 months and now again with the weather hot/dry is overboost happening. I thought cool/damp conditions would have highlighted any deficiency, denser air etc ?
Could this problem be a oil contamination issue not a restrictor ?
My car has a 2 way solonoid. Would a 3 way help ?



18th June 2000, 23:06
Hi Steve

I have a UK my98 with a two port solenoid which has had the overboost problem on and off since new.Like you I have been back to the dealer numerous times, they normally fix it for a couple of months but it always comes back.
I have tried adjusting the size of the restrictor and this does cure the problem but also makes the car slower.

I now use the standard restrictor and just clean the boost control pipework and the wastegate solenoid, as soon as it start to overboost, this cures the prob for a couple of months and saves a trip to the dealer.

Have you topped up/replaced the oil recently,I assume you know the overboost is often caused by the engine oil level being too high,its best to keep the level under the half way mark on the dipstick.

Hope this helps


Danny Fisher
19th June 2000, 18:18

My MY97 (with new short engine) is going in on Thursday for this very problem. The dealer has had the car before but could not produce the problem, mainly because it only happened of an evening/night, but it is now producing the problem during the daytime also.

I would like to add, this problem has only happened since the new engine. Could this just be a coincidence?

So the question is could I get the dealer to swap the 2 port solonoid for a 3 port one.

Thanks Dan

19th June 2000, 21:35

Last service was in Febuary and the oil has not needed topping up since.
A colleaugue of mine in with the same MY car has had the 3 port fitted about 18 months ago and has not had the problem since. He got the dealer to fit this after numerous problems like ours. This could be my next course of action if this issue isn't resolved. Keep you posted.
My car came back once with the boost obviously throttled right back, the turbo was hardly audible at all. I think the easy fix for the dealer is to fit a larger restrictor.



20th June 2000, 21:36

How do you clean out the wastegate solenoid. ?
Just remove the pipework and squirt some brake cleaner through it ?



Chan HT
21st June 2000, 20:35
My overboost problem was caused by installing a larger than factory vacuum hoses at turbo outlet to 3 port solenoind and 3 port solenoid to waste gate actuator.Installing back the factory sized hoses cured my overboost problem.Internal diameter of factory vacuum hose should be around 3-3.5mm.My 4mm plus internal diameter aftermarket hoses cause my turbo to overboost.

Hope this will help you guys.

22nd June 2000, 00:51
Hi Steve

I remove the pipes and solenoid from the car then fill it all up with spray gunk, especially the bit of pipe with the restrictor in (you can feel the bulge in the pipe where it is fitted).I use a 12v car battery charger to operate the solenoid to make sure the gunk cleans the valve seat.

After 10 mins or so I flush the gunk out using water then blow the water out using an air line(after connecting the charger again to open the solenoid).This method always works for me http://bbs.22b.com/ubb/smile.gif

Before cleaning, my solenoid is normally quiet but after you can hear it clicking.
Most people think it is wrong for the solenoid to click but when mine clicks there is no overboost and when it goes quiet the overboost returns.

I'm sure the threeport solenoid would solve this problem but it would probably take a few trips to the dealers before they get it set up properly http://bbs.22b.com/ubb/frown.gif


Chan HT
22nd June 2000, 20:25
Fit an oil catch tank/breather tank to prevent engine oil mist present in the engine intake area and this will prevent clogging of wategate solenoid.Oil catch tank is a must if doing high boost.Hope this help.

Chan HT

Danny Fisher
22nd June 2000, 20:34
Spoke to the dealership today, they confirmed that it was an oil mist problem on the solenoid. And before I could even get close to asking for a 3 port beastie, they told me 'No Sir!' subaru just wouldn'y sollow it.

Oh well. lets hope this fixes it. If not I might try the catch tank idea


23rd June 2000, 07:24
Where is the solenoid located.....driver side strut turret??

I think my car is starting to suffer from the same thing.

Has anyone got a piccie??


23rd June 2000, 23:00
My dealer suggested that I came down and went out with the Technician and satisfy myself all was ok. When the car went in the previous week only the Solenoid was cleaned, this time all the pipes were cleaned as well.
We set off with the diagnostic device plugged in under dash and were measuring for vacuum (Hg)?, the overboost cutout occurs at 800Hg. After several runs the maximum we could get was 730. The car felt a little sluggish so we fitted a different restrictor and now got 765, the car performing much better. So far so good. I think now i'll try the clean out first before any other action.

Thanks for all your help.


Yes , the solenoid is on the left hand turret. Follow the pipes and they lead to the Turbo area.

Danny Fisher
25th June 2000, 13:56
Right, picked the car up yesturday morning. And what a joy to get back in to the car of FUN.

The dealership had changed the complete solenoid and cleaned the pipework. Testing this, the car started by only boosting to about 14 then dropping to 13, so I kept pushing it, last night it would boost to about 15.5 then drop to 14 and hold until about 5000rpm then it would drop quite a bit.

So I think the next stage is to go back to Powerstation and get two things done.

Firstly get a run done and findout how things look, and secondly get the geometry setup done.

Shall report back when done.


25th June 2000, 15:01
so sorting the geomtery will make your boost higher will it Dan?

Danny Fisher
26th June 2000, 19:46
Sunil, I wish I could live in that world of yours.....

You know what I mean, now that I wont be headbutting the steering wheel, and have had the geometry setup properly, I'll have nothing other than my bad driving to blame.