60 replies to this topic

[migoreng]

Hey guys,

Anyone know why a B4 will limit boost to about 0.5 bar? Valley of death is still there, boost drops to 0.3 and secondary turbo boosts back to about 0.5 bar.

I parked the car, turned it off and its boosting normal again. It seems like the ecu is limiting boost for some reason? But why does an engine restart fix it?

It happened once a month ago and occured again this morning. Other than that, the car drives fine. I havent done anything unusual. Petrol is 98 Ron 1/4 tank atm. All engines fluids are good. No CELs. Car is stock apart from a hurricane? cat back.
Apparently the previous owner replaced the o2 sensor already last year.

Cheers guys.

[migoreng]

Hey guys. I checked for ecu codes. Nothing. Cel just flashes rapidly.

So what could it be? From what I've seen the car will probably drive normal tomorrow and then suddenly restrict boost to 0.5 bar a few days later.
it happened again today half way through a trip. I drove 15km home without problems but can really notice less power with the throttle down and boost is not building higher than 0.5 on the primary turbo.

Maybe the car just needs an upper engine clean and Italian tune up to free up any gunk in the twin turbo system?

[Mosti]

Sounds like it has gone into LIMP mode maybe? If the ecu detects serious pinging (detonation) it sometimes goes into LIMP mode which doesn't allow the car to boost. It can either reset itself or you can reset your ecu which shod fix it. That is if that's the problem

[Tim.]

Broken knock sensor causing the limp mode?

[Adam]

Knock sensor would cause a code?

Mine would still boost up. But would just have no go.

[migoreng]

Well i'm still getting boost.
If I wide open throttle after taking off, boost would hold at almost 0.5 bar, drop 0.2 or so due to valley of death, then boost up to 0.5 again with the secondary turbo.

Boost is not erratic or anything. it doesn't fluctuate. It's like there's a boost limiter for some reason.

I'll definitely pick up a can of upper engine cleaner soon but my oil change is not due for another 2000km.

[migoreng]

Thanks Kong.I just hit 180,000km. UEC was last done at 170,000km but do you trust Repco service centres?

It's a random problem I've found. Turning the engine off and on again may not fix it

[TSG]

Sounds awfully similar to a mates WRX when it had a dodgy knock sensor. However that would 'flicker' the CEL randomly, sometimes on, sometimes off. It would boost but not fully. This can result in LIMP mode...

Open throttle on a B4 should be about 14psi on the primary, drops back to about 12 after VoD. On my auto anyway. Which is around 1bar, back to 0.8bar.

[Zac]

Sounds awfully similar to a mates WRX when it had a dodgy knock sensor. However that would 'flicker' the CEL randomly, sometimes on, sometimes off. It would boost but not fully. This can result in LIMP mode...

Open throttle on a B4 should be about 14psi on the primary, drops back to about 12 after VoD. On my auto anyway. Which is About 1bar, back to 0.8bar.

I need you to test drive my car and tell me if its running right... but you are a billion miles away...

[TSG]

Well that's assuming mine runs right its not perfect by any means. Did you end up installing a boost gauge? Very satisfying mod.

[Zac]

Well that's assuming mine runs right its not perfect by any means. Did you end up installing a boost gauge? Very satisfying mod.

Not yet... must do that... Adam's exhaust first, then tint from Shaz, then probably boost gauge... Seems like its necessary to know if TT are boosting right...

[TSG]

It's only hard because you need a degree in engineering to understand how it works I'm sure people with Supra/GTR/300ZX etc etc all suffer from moron mechanic syndrome. It's unfortunately not as simple as most lego Subaru's, so probably surprises most of them going into it. But its not terrible either.

Our current mechanic sends his guys to study the latest stuff so they have some idea. Because they need to know how to work on hybrids, turbo cars, etc now. I always look for a clean workshop with modern gear. Usually an indicator that a moron or old school mechanic isn't running it.

In any case, they managed to service it without breaking it. I specified they don't do anything with the turbos/lines/black box unless the service manual says to do something there. He did pull the intercooler off and clean the throttle body etc, cause it has a new clamp. Runs as good as ever now, with a smoother gearbox. Would take it elsewhere for turbo work - or have a go myself heh.

[migoreng]

Does sound like limp mode ...... for what reason though? Is your MAF clean or shitty black?

The sensor to the right of the air filter?

I drove 30km home.. Was boosting any chance I could...flogging 1st 2nd and 3rd gears on the highways and motorway and trying not to break the speed limit.

I must have hit redline at least 10 times and engaged the secondary turbo a dozen or so times.

No problem at all!
I was enjoying the "shoved back into the seat" at 5000+rpm.

[TSG]

Sometimes you have to give it some stick just to blow out the cobwebs. Runs better after that. I find anyway

[migoreng]

Sometimes you have to give it some stick just to blow out the cobwebs. Runs better after that. I find anyway

yeap...I gave it a good flogging down the motorway again today...boost is strong! I dunno. maybe something moved around the turbo system and clogged a sensor/tube for a while?

I will continue blowing out the cobwebs tomorrow

And will check the sensor too when I can find some electrical cleaning spray.

[allpaw4]

Agree - clean out all the vac lines to and from the BBOD. Clean all solenoids. Be careful what you use to clean, make sure its plastic safe. CO Contact cleaner is great stuff. Dont use the NF stuff, its not good for plastics.
Good to hear its cleared up, but unless you have cleaned something, chances are it will be back.

[Jovi]

When it does that back off the throttle and give again and see what happens.... Mine does that in top gear wont boost over 5 psi and when i back off it goes again....i think its the issue with the waste gate controller