D-RB5

Hi,

I have had my scooby since monday and I have noticed that sometimes when I boot it, the boost comes in and then after like half a second drops off usualy around 3-4k, if I let off and slow down when boot it again the boost is normal. Its happens only now and again, but its at least once or twice a day.

I am still a scooby newbie, can someone help?

The car is a RB5 MY99 with PPP

Cheers

D

[Edited by D-RB5 - 5/16/2002 9:27:22 AM]

iain atkins

Could be hitting overboost??

D-RB5

I am newbie!

Whats overboost then?

How do I stop it, I have used Optimax since I got it forgot to add that.

iain atkins

Overboost is when the ECU senses too much boost, and it cuts fuel as a safety feature. This can be caused by oil in the boost control solenoid, which can be cleaned out with brake cleaner, or carb cleaner. This would occur especially after a service, if the oil has been slightly over filled.

Another thing it *could* be is your 'Air Flow Meter' these are a known fragile point of Scoobys and are known to fail especially if you have an aftermarket foam oil filter. This is because the oil (which helps trap the dirt & dust in the filter) can get sucked into the air flow meter and contaminate the sensitive components of the meter.

Has your 'Check Engine' light ever come on?

Cheers



Iain

D-RB5

Ahh thanks,

My check engine light has come on once, when I was tanking it down the A1M after a bike :0, I am taking it back to the dealer on saturday for them to check that out. But the light has never come on when I have had this drop in Boost problem.

D

[Edited by D-RB5 - 5/16/2002 9:49:50 AM]

iain atkins

Ask them to use a select monitor on the car, and mention that the 'Check Engine' light has come on.

Good luck, let me know how you get on.


Iain

D-RB5

OK quick update,

I am still having problems, I have taken the car back and they have replaced the Oxygen sensor. But I am still getting no boost or low boost sometimes. I was wrong in my previous post the boost simply doesnt come in and drop. It doesnt come in fully. the wierd thing is if I let off the gas for half a second and put my foot down again, it comes in properly.

Can anyone help me with this,

Cheers

Dwayne

john banks

It is a tricky one to sort out without seeing it or datalogging it. There is an noise control system in 2nd gear where if you have been on light throttle at 3000 RPM and then floor it you only get half boost - a lift and reapply cures it.

On an overboosting car it would feel much smoother at 3/4 throttle than full. The vast majority of time it does not actually cut the fuel but alters the wastegate duty cycle to control the boost. To be able to help you more without seeing the car you need to have a boost gauge.

Otherwise just pester the dealer to sort it. If they don't find another that will.

D-RB5

Thanks john,

Whats this noise control system? That sounds exacty like what I am getting, after you mentioned that It only seems to happen in 2nd. Usualy if I drop it into second and then have it on light throttle while I am waiting for an oncoming car to pass before I overtake.

Dwayne

Pete Croney

Sounds like the ECU routine to get the car through the drive by noise test.

If you hold the car for longer than a certain periodin 2nd, and then nail it, it only produces half boost.

If you give it a prod and then apply full throttle, it will give full boost. It will also give full boost if you don't hold a steady throttle for very long.

D-RB5

Coo,

thats abit wierd, can I turn it off anyhow? Do is it just a case of changing driving style?

Dwayne

john banks

You end up driving around it.

iain atkins

Yep,

Just to confirm above posts from Pete & John. If it is happening in second gear only at about 3,000rpm then it will be the noise control.

You will get used to it.

RT

YES, it is DEFINITELY the noise test phenomenon. Basically, Subaru gets thru the 50kmh drive-by noise test by building this feature into the ECU. If you're in 2nd gear, hold it for a few seconds, and then give it WOT immediately, you WILL get 0.5bar boost and no more. I was able to reproduce this at will on my MY99.

Don't worry too much. Just give it gentle (but brisk) throttle opening. Doesn't slow you down at all, and you'll get your 1bar.

Flat 4x4

Thanks everyone - now I know what's affecting my MY99 as well (AE800).

I didn't think it was overboost but cleaned the pipes, had the ECU reset at the dealer, stuck to Optimax etc. I will now adjust my driving style in 2nd gear and forget about spending money on having the ECU remapped.

This should be posted in a FAQ / common Impreza quirks list.

john banks

Like the cold start slight hesitation, this is unfortunately something that we will have to live with with JECS remaps as well. But the other advantages make up for it.

RT

Its amazing that the dealers don't know about this.

TG4Scoobynet!

D-RB5

Well,

You guys deserve a pat on the back, I was able to reproduce this at will on the way home from work last night, and it IS the exact thing I was complaining about.

Thanks guys!