ROBERT BARNES

Hi people seem to have a boost problem with my MY97 just fitted a scooby sport down pipe to my blitz centre and tailbox was ok for about 10 days,and no had no problems, but today i find on acceleration when the boost is rising the engine is cutting dead for a few seconds looking at the in car boost guage when this happens it is reading 1.7 bar well over the normal also when not boosting ie on tick over the gauge is reading alot more negative boost,i also have a induction kit fitted and a blitz dump valve but these have been on over a year,oviously somrthing has failed but not sure what and do you think the scooby sport down pipe has anything to do with it or is it just coincidence the car has covered 22.000 miles and is standard apart from the above modifacations, any ideas thank fully recieved cheers rob

MarkF

Rob have you checked all the pipes etc in the downpipe area? Could be that you've accidentally knocked something off while working around there. Fitted my SS downpipe and had no problems with the car afterwards.

dowser

Has you just filled up the oil? The boost control solenoid valve and associated hosing can get oiled up and cause this problem....normally after oil change and car is over-filled slightly.

1.7 is very high

Richard

ROBERT BARNES

i done a few more test and its still the same cleaned the small VAC pipes on the o/s inner wing to all the soleniods etc, and they seemed very clean could blow through them no problem, and the out lets on the manifold were also clear,also tried disconnecting my boost gauge and it still did it, i got a passenger in and got him to watch the boost guage when it happened as its hard to see when driving its actually about 1.3 to 1.4 bar not 1.7 these blitz gauges arnt the easyest to read on the move, which one is the boost soleniod and how do you test it my dealers anwser was fetch it in it could take anything from 20 mins to 2 days to sort out as they would,any more advice would be very thankful could the actuator have out to do with it ??????
sick as a chip....

[This message has been edited by ROBERT BARNES (edited 19 February 2001).]

ROBERT BARNES

can anyone tell me if you remove the boost control solenoid from the inner wing and try and blow through the two vac unions should the air go through mine does not and the pison does,nt seem to move ethier should i try pussing it up manually through the bottom vac union or not don't want to break it you see...

ndouglass

Rob,

Have you tried spraying some Aerosol Brake Cleaner in the Boost Solenoid, disconnect the pipes spray a bit of Brake Cleaner inside and connect the two black connectors together under your steering column.
Then turn the ignition two clicks, not turning over and you should hear the fans click in and the solenoid cycling through in test mode.

Make sure you have a cloth covering any exits on the solenoid so you don't get any crap on your paintwork.

Neil

ROBERT BARNES

removed and cleaned the solenoid and refitted and tried it and now its the opposite only 0.6 bar now maximum, i mean what the fek is going on here could it be siezed open now after i poked about a bit ???? how much is a new one neil can i try yours on please ????

[This message has been edited by ROBERT BARNES (edited 19 February 2001).]

Rikki23

Hmmm interesting. I have been having overboost problems at about .9 Bar on my 95 WRX. Lavender Hill have all but sured it by putting in a restrictor which has reduced pressure to 0.6 - 0.7 Bar, which I didn't want to happen. Is it just a coincidence that it is this value, with regards to what has been said above.

I am going back on sat to have the restrictor removed as I want the extra boost and as I start doing mods (exhaust, industion etc) I do not want the restrictor to reduce any gains these mods could give me. Does this sound sensible?

NITO

Stock boost on my MY98, ie the boost produced when the boost solenoid isn't working is 0.45bar. My car originally started with its overboost problem when it was bog standard, boost would swing to about 1.2bar just over and it would cut. I then fitted the free flow exhaust/downpipe and induction and boost was trying to reach 1.35bar which it did for a couple of seconds before cutting out. This is the traditional overboost problem and the dealer fix was to put a restrictor in. This limited my car to about 0.7bar in the first three gears rising to about 0.8 in 4th and 5th. Needless to say it was pants which is why I fitted the electronic boost controller! What you have described is normal behaviour with many scoobs, the fitting of the downpipe exaggerates overboost problems. The overboost shouldn't be there in the first place it's mainly coz the subaru boost solenoid is a piece of crap. Later cars with the three port solenoid are better apparently. With regards to it only making 0.6bar now, are you sure all the vacuum hoses/electronic wires are properly attached. If it's not this then it's more than likely the solenoid up the creek.

Rikki, that's the restrictor limiting your boost to 0.7bar, obviously your car suffered from the overboost to the degree that mine did, ie pretty bad, some cars only have it marginally. They can experiment with different size restrictors, but even then, you'll still be getting boost cut probably in 5th occasionally which is dangerous as it could happen when you least expect it while overtaking!

Nito

dowser

Robert

0.6 bar is around the level you'd expect if the solenoid was not operating (thought it was .7) - the system is designed so that if it fails the solenoid remains closed allowing all the pressure to go to the wastegate. Your boost control is currently the pressure of the wastegate spring!

Did you refit everything correctly? Pipes and connectors. As mentioned above, joining the black connectors will put the car into 'mad-cow mode' cycling through all solenoid, fan & relay functions. You should be able to hear the solenoid clicking as part of this cycle.

Hope that helps
Richard

ROBERT BARNES

dowser i will try the above also it may be 0,7 bar or there abouts as it quiet difficalt to read my boost gauge on the move so your probably right i wonder how much a new one is then ????

ndouglass

Rob,

Found this thread maybe of interest to your Overboost problem, hope you get it sorted out real soon.

ROBERT BARNES

Just another twist to the tail when i removed and cleaned the soleniod i found the tinyest of splits in the Vac pipe from the throttle body to the T piece that goes to the actuator,which i replaced at the same time, after speaking to Gilesgate at hexam they informed me that the pipe i had replaced had a inline restrictor in it this causing my low boost problem as the replacement was just straight pipe.and a repair to this pipe had to be made which i haven't done as yet,i assume this will give me back my original problem of over boosting when its refitted and repaired unless cleaning the soleniod has worked like,at a cost of £80.00 a throw i don't want to go out and get one just to try in case its not that.don't suppose anyone has a good one lying about i could try do they,i will keep you posted when i refit the original vac hose back on and see what happens from there any more suggestions are thankfully recieved cheers Rob...

AndyMc

Just to clear up a bit of confusion about the boost restrictors.

All cars that have a two port solenoid have a boost restrictor fitted from the factory.This is NOT there to restrict the performance of the car, it simply allows the solenoid to work properly.The fact that your car has a restrictor does not necessarily mean it's performance has been reduced.

-If you remove the restrictor on a 2 port solenoid equipped car the boost will drop to about 8-9psi
-If you fit a smaller restrictor the boost does run higher but this is only because the solenoid is prevented from working properly.The ECU now has no control over the boost level which can make the car overboost.

-If you add things like air filters and downpipes the boost rises more aggressively and this can often lead to overboost.It may be necessary to fit a slightly larger restrictor to overcome this problem.

The other common problem is that the restrictor and solenoid become coated in oil from the breather system.The standard restrictor has a 1.2mm hole(well my MY98 did,I believe the imports have a smaller one).A change to a 1.1mm restrictor was enough to cause overboost on my car so you can see the system is very sensitive to the size of the restrictor.Just a fine mist of oil coating the restrictor can reduce the size enough to cause the overboost.Basically the design is crap but fortunately this problem can nearly always be cured by cleaning the pipework, restrictor and solenoid.

Unfortunately a lot of dealerships have cured this problem by fitting a different restrictor with a larger hole.This does cure it but has the completely unacceptable side effect of reducing the boost and making the car slower.It may be the case that this has been done to your car if the boost is running at a low level .

The restrictor on my 2 port MY98 is located in the rubber hose which is connected to the discharge of the turbo just to the lefthand side of the intercooler.This hose then splits into two separate pipes one of which goes to the wastegate actuator and the other goes to the wastegate solenoid on the driverside strut.The other pipe from the solenoid connects to the large pipe that comes out of the airfilter housing.

All of this applied to cars that have 2 port solenoids.The three port solenoids have the restrictor fitted in a different pipe and changing the size has the opposite effect ie a smaller restrictor lowers the boost.

Hope this helps somebody

Andy

NITO

Not meaning to doubt your experience Andy, but with mine MY98 it worked the opposite way. Mine didn't have a brass boost restrictor originally (at least not in the place where the restrictor is located on mine) and one was fitted in the vacuum hose that comes off the airbox or just to the right of it by the manifold (have to look at it to make sure) (I have a picture of this so when I'm at my home computer I'll put it up showing the restrictor location.).

By fitting a restrictor with a smaller diameter my boost was reduced and one with a larger diameter and it was increased. I think it is the three port that works the other way around, ie smaller hole=more boost and vice versa, of course it may just depend on which hose the restrictor is located in. As for all of them coming with one (not a restrictor but a brass piece to help boost control), I can't comment as I didn't check the rest of the vacuum hoses as my dealer just showed me what they had done and where they had fitted it!

Nito

jack

I'm fairly certain the factory boost control system is running open-loop, meaning the solenoid will always work at the same duty rate, regardless of the number of restrictors used and their positions. This is why we get different boost in different seasons, altitude etc. Using different size restrictors and putting them at various positions is the only way to control what peak boost you get.

In order to achieve the same boost no matter what conditions, you'll need an electronic boost controller that works in closed-loop.

My 2 cents.

AndyMc

Hi Nito

I'm not sure what is going on with your car. Might the dealership have played with it before you bought it! Maybe some did leave the factory set up like you have described.If they did I can't understand how they work though.
Besides my MY98 I have looked at three other scoobs with a 2 port solenoid,two were MY99's and one was a MY2000. They were all exactly the same as mine(restrictor in first pipe off the turbo).I have also read all the posts on overboost etc for a while now by the likes of Bob Rawle and I'm sure they said the same thing as my post above.

If you look at Lee C's site there is a picture which shows the location of the restrictor on his MY99 2port equipped car.Pipe B on Lee's diagram had the restrictor fitted,same as all the cars I have looked at .The diagram is under 'my car'then 'mods' then 'boost increase'

Mac's Power

You guys seem to know what you are at.
Would you mind helping out a customer of mine by cheking out

ROBERT BARNES

ITS FIXED super guess what it was,the pipe i replaced had a tiny split in it (causing the over boost problem)and i did'nt realize when i replaced the pipe that it had a restrictor valve in it, replacing it with standard vac hose, the lack of the restrictor causing the under boost problem,so i repaired the split pipe and whala fixed back to 1.2 bar boost and holding 1.0 the way it was before, this pipe must of got damaged when the front pipe was fitted,the pipe in question was the 3" long one from the inlet manifold to the plastic T piece which then splits into two one to the actuator and the other to the vavle,oviously this system is very sensative and any air leak will result in the same as a minute split in the pipe,may be worth a try checking on anyone who still has a problem you never no thans for the advice lads it won't be forgotten cheers rob...

[This message has been edited by ROBERT BARNES (edited 21 February 2001).]

Jacko

Hi Robert,
I am interested in what you did to eliminate your problem. I also have 97MY and would like to flush out all the vac hoses and check for damage. I would also like to know where the restrictor is located. I can't seem to find it.
The dealership over filled the oil level and I think I have a possible boost problem. Probably also need to clean out the Boost Solenoid.
Is there a engine bay photo with the right hoses to disconnect and restrictor, etc to look at???????

Glad to hear you sorted it...

Cheers Robert.

NITO

Well Done Robert.

Jacko, not sure about later cars but for MY97/98 restrictor went here (at least on my car anyway) Excuse the filthy engine bay, it was before I cleaned it anyway, if you look in this hose, ie where the larger hose from the airbox joins the smaller diameter hose, if you can see a brass restrictor in the smaller diameter hose then you have a boost restrictor!



Nito

WRX500BHP

talk about boost, if anyone is interested please see my post in drivetrain section, "list of parts for sale". I have boost controller for sale.

Cheers,
WRX500BHP

pat

Hi All!

Just to clarify a few things...

The term "boost restrictor" isn't exactly accurate, it doesn't restrict boost ;-) The function is quite simple really... I will try to explain:

As the turbo spools up, it begins to pressurise the wastegate actuator. This will open up at some pressure (depends on actuator, turbo etc), typically between 0.4 and 0.7 bar boost. As it opens, it allows exhaust gas to bypass the turbine, thereby reducing the amount of boost. Since adjusting the wastegate actuator to operate at a higher pressure isn't easy (or possible in some cases) what is needed is a pressure divider....

Say that we have an acutator which opens at 0.5 bar boost and we want to run 1.0 bar boost, then we need to divide the pressure by 2; so 1 bar boost at the turbo outlet (2 bar absolute) equates to 0.5 bar boost at the actuator (1.5 bar absolute). This can be done with a PAIR of restrictions, the first limits flow ONTO the wastegate actuator and the next one limits flow OFF the actuator. If they are chosen correctly then the turbo will generate 1.0 bar boost, given that atmospheric pressure is 1.0 bar absolute.

It gets interesting if atmospheric pressure falls. The actuator still requires a pressure difference of 0.5 bar across it. So say we go from 1.0 bar atmospheric to 0.6 bar atmospheric (quite high up a mountain). We then need 1.1 bar absolute on the actuator to open it. But our divider will require 1 bar across the divider to give 0.5 bar over atmospheric at the actuator. So the actual pressure we will see is 1.6 bar. This is a problem!

At 1 bar atmospheric, the pressure ratio between the turbocharger outlet pressure and atmospheric is 2:1 (2 bar absolute as opposed to 1 bar atmospheric). Now look at the "up a mountain" scenario, we have 1.6:0.6 or 2.666:1. The turbo is raising the pressure of the air MORE, it is therefore working harder. This usually means it is spinning faster; it is possible that at this pressure ratio, the impeller tips may go supersonic, this is a Very Bad Thing (TM), and can cause the impeller to explode!! To get round this problem, we can use a "variable" restriction to control flow OFF the actuator....

Assume for a moment that it is completely blocked, then the actuator pressure will be the same as the turbo exit pressure, so we are back to square one, the turbo will generate between 0.4 and 0.7 bar boost. Now assume that we open it up so that the flow off the actuator is not in any way impeded, then there will never be any pressure on the actuator; this would theoretically keep increasing boost indefinitely, but it won't because the turbo may go supersonic, the engine may blow up, or the pressure of the exhaust gasses on the wastegate are so large that it just gets blown open due to exhaust backpressure. So we have two extreme examples.

Now say we turn it on and off repeatedly, and keep the rate at which it flows when open to a "sensible" level (it pressure takes time to collapse, doesn't just vanish all at once). We can now control the amount of flow off the actuator, thereby controlling the pressure on the actuator. So we have two restrictors again, but the second one has a resistance to flow which is determined by the ratio of the time it is ope to the time it is closed (more commonly called duty cycle).

In an Impreza the wastegate actuator pressure control solenoid performs this function, it operates at 12Hz. Each 1/12th of a second is further subdivided into an "open" time and a "closed" time, so at 50% duty cycle it will stay open for 1/24th second and closed for 1/24th of a second. At 25% duty cycle it will be open for 1/48th of a second and closed for 3/48th os a second, and so on.

Now we look at overboost (at last, eh? LOL). OK, the ECU "knows" that to get 1.0 bar of boost at 1 bar atmospheric it will need to have the duty cycle at about 50% (for example, it could be anything, but we'll use 50%). So say we put a smaller restrictor between the turbo and the wastegate, then it will take longer for the wastegate to pressurise (think of inflating a baloon to a set size through various sizes of hose, the smaller the hose, the longer it will take). Also, because there is less flow onto the wastegate actuator, yet we are still flowing off it at the same rate, the pressure divider will be greater, that is it will require more pressure at the turbo exit to get that 0.5 bar boost on the actuator. OK, so the boost builds and promptly overshoots the target, so the ECU pulls back the duty cycle so it is reducing flow off the actuator, thereby increasing the pressure on the actuator and hence opening it, and reducing boost. Conversely, if we fit a larger restrictor, the duty cycle will now be too low, and boost will hit (say) 0.7 bar, the ECU will think "hey hang on, that's not enough!" and increase the duty to allow more flow off the actuator thereby reducing the pressure on it and closing the wastegate, thereby increasing the boost pressure.

Another problem is that of "delays". Recall the analogy of the baloon and various hoses. Say we completely block off the valve so we can't allow pressure off the actuator, so we would expect to see about 0.5 bar boost. But now assume that the restrictor is simply too small, it will take time to pressurise the actuator as a result. So it is possible that the boost will hit 0.8 bar, then fall back to 0.5 as the actuator is pressurised.

Good boost control relies on these individual influences being "in harmony" with eachother. It takes a long time to get these "just right", and of course there's always manufacturing tolerance. The Toyota workshop manual makes me laugh... their actuators are specced "between 0.5 and 0.83 bar", and their engines (3S-GTE anyway) do not use a solenoid in the same way as the Subaru does, result is pretty much pot luck as to what boost you get!

Finally we get to a 3 port control solenoid. This is "the daddy", since it does not require restrictors (although it does work better with restrictors on a PossumLink and the Subaru engine management system). The 3 ports are: turbo exit, wastegate actuator and air. It has two "states", that is actuator connected to turbo exit (to pressurise the actuator) and actuator to air (to depressurise the actuator). If the control system is good, this can control boost VERY well, and it will also have an extremely quick response because there are less "delays" due to restrictions. I am using a 3 port with no restrictors at the mo and it seems to work quite well :-) But I will be looking at building a ball/spring variable valve, which should be very interesting indeed.... just as a comparison if nothing else.

FWIW, to the best of my knowledge, the Subaru engine management DOES use closed loop boost control (ie it varies the duty cycle to control boost), AND it will reduce the boost, as atmospheric pressure falls, to protect the turbocharger from overspooling (going way out of it's efficiency band, and/or going supersonic).

In Robs's case, the split pipe allowed pressure to escape before it got to the actuator, thereby increasing the boost level required to open the actuator.

Hope this helps,

Pat.

ROBERT BARNES

Jacko i carn't really add much more to the above really just that my valve/restricter was in the pipe from the inlet manifold to the plastic T piece as where indicated in the above photo,but you can not see it as its internal and all you can do is feel the pipe along untill you feel it inside,airosol brake cleanes or carb cleaners are the boys for cleanig out the pipes and valve,if you remove a pipe at a time and flush them out and then go on to the next etc you will have no problems i feel for anyone who has this problem as it did my head in for three days and the dealer answer was the best i quote,(err it could be out mate)any idea of price to find out what it could be i said(well anything from 1 hrs labour to 20 and £20 to £2000)was the reply i mean, kin hell sort of answers are these like

dowser

Thanks Pat

Since fitting a decat downpipe to a PPP'ed my00 I'm also suffering from poor boost control - seems that the turbo is spooling quicker now, but the solenoid loop is still responding at the same speed. Result: a peak boost of 1.35 bar....lasting for just over a second (don't *think* that's very healthy - knocklink on order [BRD, please!]).

I'm going to experiment with the restrictors to see whether I can improve the response time - is there anything else I can try?

I've refitted an STI backbox at the moment, the added restriction improves the boost control

Cheers
Richard

Andrew O'Hara

My P1 has been suffering over boost, had all the pipes form solenoid to actuator cleaned out, and for the moment seems to be cured.

A mechanic at the dealership suggested an in-car boost controller, which could help in the interim if you can turn down the boost while driving. I called Demon Tweeks today and was quoted £48.43 for a full kit.....I would appreciate peoples comments as I am considering getting the kit.

Cheers guys

Andy.