GREGGYG

iTrader: (2)

My local Subaru main dealer is unable to find what's wrong with my car's low turbo boost problem. It always felt on the slow side, so I took it for a check, and the result was that the turbo had a maximum boost of 0.7 bar, rather than the approx. 1.2 bar which it should be producing. The car drives well, makes all the right sounds, no visible oil leaks from turbo, fuel consumption ok, no flat spots, nothing out of the ordinary whilst driving, other than no strong pick up from the turbo. (Sometimes it can feel quite quicker than other times, not weather temperature related)

Car is a JDM STi 2003.

I don't know what to do now, the main dealer said they checked every sensor and other electrical item on the car relating to the turbo, and all is working well. They said the fault 'could' point to the turbo itself, and I cannot find a single thread or website which talks about failed vf37 turbochargers, in other words, it seems evident that these turbo's do not fail that easily, and at the low mileage my car has done! Does anyone have any ideas or suggestions, as I cannot afford to take the car to other garages to diagnose a turbo fault which I feel a Subaru main dealer should be able to do fairly easily. It has already been to one garage previously, who are experienced with Subaru's, and without examining any part on the car, they said my turbo needed replacing, which I felt was a premature diagnosis, as it was done soooooo quickly. (Maybe they are right!)

What do you think? All help and advice much appreciated, as always.

banny sti

iTrader: (68)

Have you tried resetting the ecu? As the car may have detected knock at some point and retarded the timing and boost.

Banny

GREGGYG

iTrader: (2)

Thanks Banny, I would like to think the main dealer did that as a matter of course! I'll ask them in the morning when I collect the car.

Ive also tried octane boost as suggested in a previous thread, and it made absolutely no difference in power. (Usually use Tesco 99 or Shell V Power)

banny sti

iTrader: (68)

0.7 bar is actuator pressure, so it maybe worthwile getting the actuator checked or the boost solenoid piping maybe incorrect. It seems unlikely that the turbo would fail so easily and you would get the tell tales signs of blue smoke from the exhaust and some sort of turbo whine.

JohnD

iTrader: (5)

My sons STi PPP had low boost and it turned out to be a blocked restrictor in the actuator pipework. Get them to disconnect and blow through the tubing.
JohnD

Multijfj

This hapend to me, reset the ecu, and it turned out to be the fuel I put in wasnt good enough for the car. Now it boosts fine after an ECU Reset, some steady driving, and 2k miles later we are still going strong.

Coffin Dodger

Happened to mine as some donkey Subaru main dealer mechanic had blocked of the bleed pipe from the boost solenoid with a screw after I had complained of an over boost problem. Went from over boost to no boost. Thought it was a bit slow when I picked it up.

Either get yourself to someone who knows what they are doing (API, PowerStation, ScoobyClinic etc.) or to test the turbo get yourself a manual boost controller (Dawes device) and a boost gauge. Fit the Dawes, set to lowest setting, go for a drive and record peak boost on the gauge, and repeat the process winding it up half a turn or so. If the turbo never makes 1.2bar boost then its fecked. If it does then there is something wrong with the boost control - try the solenoid, pipe work, etc.

APIDavid

iTrader: (4)

Just remember with the Dawes that there is no scaling for the boost. Whatever you eventually set it to - let's say 1.3 bar. It will crack at 1.3 bar all the way through the rev band rather than be scaled electronically from say; 0.75 bar up to 1.3 bar and reducing to .75 bar at 7000 rpm [ for the sake of this argument ].

Flat line boost like a Dawes provides can be dangerous and there is always the fear that the car will feel slow one day, or the driver get used to the current figure and ' give it another half turn ' and so on. Then one day the boost is now 1.8 bar flat line and the engine goes pop!

Used carefully and under controlled circumstances there is a place for bleed valves. But NOT as the primary source of boost control.

David APi

Coffin Dodger

Agreed

All I was suggesting was rigging up a Dawes to ensure his turbo can make 1.2bar boost in the first place, i.e. it isn't fecked. Removes all the uncertainty of the boost control system. If the turbo proves to be fine then remove the Dawes and track down the problem with the boost control from the ECU. Dawes devices are a cheap if slightly crude mod, but yes ECU boost control all the way if you value your engine.

Anyhow, unless he fits a fuel cut defender as well, the ECU will stop you from winding it up to 1.8bar and stop such "give another half a turn" tomfoolery

1168

i dont no if its the same with the impreza but problems with low boost on my rs turbo i had years ago was always down to actuator adjustment.as far as im aware all turbo engines are the same basic setup.good luck

GREGGYG

iTrader: (2)

Thanks a lot for all your replies!

I spoke to the supplying dealer today where I have a 1 year warranty with the car, and he's advised fitting a new posting 'boost control solenoid', which he's posting me tomorrow, to fit myself, and if that doesn't help, then he will take further action. Apparently, this boost control solenoid is easy to fit, 2 bolts, so I will post back once I have the part and have fitted it.

I would have thought a Subaru diagnostic device would have picked up a faulty boost control solenoid?

KenS55STI

If the boost solenoid doesn't sort it then I'd suggest going to see an independant subaru specialist rather than a main dealer. You generally get better service at lower prices and they are more likely to have dealt with JDM cars than the dealer. Your car has a twin scroll turbo and these are not fitted to any of the uk versions.

Andy.F

Have you had it since new ? If not, try pressing the HRW switch whilst on full throttle

Andy

Multijfj

What is the HRW switch, and what does it do by pressing it on full throttle?!

Multijfj

What is the HRW switch, and what does it do by pressing it on full throttle?!

RON

Heated Rear Window.....

If the car has been mapped with 2 maps, the process of full throttle and pressing the switch changes it between one map and the other.....

Andy.F

Heated rear windscreen, rear demist.
If it has been previously remapped with twin maps, this is how you select the high/low power maps from within the car.

I have had someone turn up for mapping and all I needed to do was press the button to give him some 60bhp power gains I had mapped it for the previous owner who later traded it in at Subaru and 'forgot' to mention it was modified !

Andy

RON

Did you charge Him Andy??

GREGGYG

iTrader: (2)

Thanks Andy, I will try that in the next few minutes when I go out! Do I press the switch on then off, or keep it on?

I should have that boost control solenoid hopefully in the morning, and once I fit it and test the car I'll post back. i must say thought that the car has its very rare moments of feeling lethally quick, but most of the time its sluggish.

Multijfj

He cant answer that lol!

Andy.F

As it happens.....Yes !! but just a nominal fee of £20 or something as he asked me to check it out to ensure it was still running like it was meant to.

It had headers, big turbo, injectors etc He was one happy guy !

Andy

Greggy, just switch it on then off with your foot to the floor. Its a slim chance but worth trying !

XR-Wayne

Did you get in his car andy and go '' I'v Mapped this already''lol

GREGGYG

iTrader: (2)

Thanks Andy, I pressed every single switch in the car on full throttle expecting a sudden full on nice kick in the back but sadly no joy!

That boost control solenoid is next, should be here in the morning. If that doesn't work, then I think the supplying dealer will have to take it in somewhere for me for a clear-cut diagnosis, ideally somewhere near where I live, West London, maybe somewhere like Power Engineering.

Scott.T

iTrader: (2)

check if there is a restrictor in the 3mm vacum pipe that connects to the turbo outlet. It should be a short section with a plastic t-piece. The other 2 sides of the t-piece go to the actuator and boost control solenoid.

Just before the t-piece on the turbo side there should be a restrictor inserted in the pipe. This is a small piece a brass with a small hole drilled through it.
If it's missing the actuator will be seeing full pressure and cracking open too soon.

I'm not sure what size hole the restrictor should have on your model but it will be something like 1mm.

The Trooper 1815

iTrader: (31)

As above. Just had a remap done at Powerstation and I had my restrictor replaced by Rich as part of the set up. The tiny piece of brass made a massive difference.

GREGGYG

iTrader: (2)

Thanks Scott, I've just checked, and there is no visible restrictor, I can feel something solid inside the 3mm pipe on the turbo side. It all looks in order, it's only a 13500 mile car and the engine and surrounding connections all look like new! I unplugged and replugged in the boost solenoid, and all it did was put the engine management light on momentarily. If the fitting of the new boost control solenoid doesn't do it tomorrow, then it will have to go to Pwer Engineering for a dyno test to establish exactly what is going on with the turbo. I'm convinced it's not the turbo, just a strong gut feeling!

Scott.T

iTrader: (2)

The something solid you found will be the restrictor.
Beware if you unplugged the connector and got the CEL on, as this will of logged a fault with the ECU. Then if someone reads the faults out they will think thats the problem, unless you tell them you done it or unless you do an ECU reset to clear the fault.

You could pull the hose with the restrictor off the actuator and plug the end. Then go for a carefull drive to see if it will boost above 0.7bar. If it does it will rise rapidly, and may hit the fuel-cut limit so be quick to back-off. But your butt-o-meter should be able to tell the difference.

This should then point the finger squarly at the Boost Control circuit.

JonMc

iTrader: (51)

Should this restrictor be on all impreza's. I've just replaced all my hoses with SAMCO because I suspected the cause of my low boost to be a leaking hose, but no change. I didn't find anything in the old hoses to move across to the new ones. Mine's a bugeye WRX. If so I need to get one, any ideas, I assume any of the tuners that advertise on here could help.

Andy.F

Or even the tuners that don't advertise

Yes you will need the original brass restrictor in place to achieve the proper boost level on your car.

Andy

JonMc

iTrader: (51)

Do you have them, and if so how much to get one from you.

I presume I just push it into the hose or is it a one way valve?