simon a

Had this problem for a month or so now, MY97 UK car with ss backbox and k&n induction kit which were fitted six months ago.
The overboost is very intermittent some days it will hold at normal boost (13psi) and others it will go round to 16 or 17 but never more than that and its usually when overtaking which is very annoying. I have done the usual including ECU reset and cleaning the solenoid none of which helped at all, i've done a search on previous threads but there seems to be no definite solution other than spend loads of money on expensive boost controllers, i would even consider taking the overboost protection out if this is possible??
any advice on this subject would really help as i'm getting fed up with driving the scoob (didn't think i'd ever say that!!)
cheers
simon

DJB

You could try a larger restrictor (small piece of brass with specific sized hole drilled in it, hidden in rubber pipe between the inlet manifold and t-piece leading to waste gate actuator). The restrictor in my MY98 is about 1.1 mm. I would suggest a slightly larger one such as 1.2 or 1.3 mm (assuming yours is also 1.1 mm). Beware, as small changes make a big difference. You should be able to get all the different sizes from a dealer.

D.

DJB

You could try a larger restrictor (small piece of brass with specific sized hole drilled in it, hidden in rubber pipe between the inlet manifold and t-piece leading to waste gate actuator). The restrictor in my MY98 is about 1.1 mm. I would suggest a slightly larger one such as 1.2 or 1.3 mm (assuming yours is also 1.1 mm). Beware, as small changes make a big difference. You should be able to get all the different sizes from a dealer.

D.

DJB

Oops posted twice.

KevinH

a really simple way is to use a bleed valve on the line to the MAP sensor.

If you want to try this out cheaply, go down your local pet shop and buy a 3 way flow control value from the aquarium section should cost less than a pound.

simon a

Thanks for the info guys
Kevin have you tried this out with the bleed valve as i've got one i could use, have you any diagrams, which is the MAP sensor ?
Also does it have to be open for it to work
Any info on this would help
thanks
simon

KevinH

Simon

Yes I have tried it, I'll email you some diagrams / photos this evening.

Kevin

AndyMc

Simon what ever you do DON'T put a bleed valve in the line to the MAP(manifold absolute pressure) sensor as you will fool the ECU into thinking the boost is lower than it actually is.This will affect the fueling and ignition.Not good

It is however OK to put a bleed valve into the lines that connect to the boost control solenoid as the worst you can do is make the car overboost more.Is this where you mean Kevin?

I have had overboost intermittently on my MY98 since new.I have discovered that it is very important for the brass restrictor to be perfectly clean so I would take it out and make sure.

My car had been OK for about a year untill I changed the oil about a week ago prior to a trackday at Oulton park and much to my dismay it came back during my third session.A boost cut halfway around druids is the last thing you want to happen I can tell you.
After I came off I managed to get the restrictor out without tools.It was covered in oil and after cleaning it I had no problems for the rest of the day and non since.
Why the problem shows after an oil change I have no idea especially as the oil level was lower after the change than before.

The fact that your car holds the correct boost most of the time suggests that the size of the restrictor is ok.As DJB says it might be worth trying a restrictor 0.1mm bigger to see what happens.A 0.1mm change in diameter has a big effect and it only takes a small amount of dirt/oil on the restrictor to reduce the diameter enough to cause a problem

What method have you used to clean the pipework and solenoid?.
I have found the following method works well

remove the solenoid and pipework from the car and connect the wires from the solenoid to a car battery charger so the solenoid opens.Next fill all the pipework and solenoid with Gunk and leave for five minutes operating the solenoid every now and again so the seat is cleaned thoroughly.Next rinse out with water and then blow out with an air line if you have one.Then refit to the car and hey presto no overboost (hopefully)

Hope this helps

Andy

simon a

Kevin
thanks for the info sent to me, don't know if that is the answer though as its an intermittent problem.
Andy
i've cleaned out the solenoid but it made no difference also had a look at the brass restrictor which was fine and all the pipework was spotless, might try some different size restrictors.

Could this be down to a dodgy solenoid ?
read somewhere that a 3 port solenoid is fitted to later cars, can i fit one of those ? whats the difference ?

simon

AJbaseBloke

A very non-tech response here, but my car had a major overshoot problem - and it went away with the install of an earthing kit.

Boost comes up nicely, does not over shoot (don't hear the alarm on my gauge anymore, or see peak records that make me sweat bullets either).

Altogether very nice indeed. Very cheap too (a DIY jobby).

Hope this helps.

Cheers.

simon a

Ajbasebloke
could you explain what to do, if its adding extra earthing points i can't see why it should make any difference
simon

Jan Shim

Here's a illustrated Earthing mod the guy did to his Subaru Legacy.