Hi guys, I don'r really understand enough about turbocharging etc to know how much of a problem overboosting is? For starters, is it actually a problem? Like could it cause damage to anything? I'm guessing in extreme cases yes it can. The reason I'm asking is, my car has suddenly started doing it. Nothing has changed car wise, not even put petrol in or anything....it just started doing it yesterday when I was driving to bristol, and also today now on the way back. Everytime I put my foot flat on the floor, it overboosts. It has done it occasionally in the past, but now it's gauranteed everytime I put my foot flat down like. I'm guessing a tiinnnnyyy bit of overboost might be normal? Especially as I've change the exhaust from the turbo back. But yeah anyway, the peak value stored by my boost gauge when I got back today........



Umm. Oh dear lol. Standard car is meant to boost at 14psi, is it? And now I'm getting nearly 20psi? Would a remap probably sort this? It's only just started happening tho, that's what I can't figure out? I set the peak warning on my boost gauge to 16psi, and it hasn't warned me for ages. I'm talkin months & months. Today and yesterday tho, everytime foot went down. Any ideas?

 

Sorry guys, I meant to mention........the boost doesn't actually stay that high......it just shoots up to that level and then settles back down to around 14/15ish

 

When you say "change the exhaust from the turbo back" Is that a decat + aftermarket exhaust? Has it only been overboosting since doing this?

I seem to get boost spike to around the same level, but then drops off to about 1.0-1.1 bar

I'll keep an eye on this as would like to know what causes the boost spike & does anyone know what a 98 sti should hold its boost at?

 

Aye yeah - Ninja sports cat downpipe, afterburner de-cat centre section, & custom hayward & scott backbox. No it hasn't been doing it since then.....the exhaust from the turbo back has been non-standard for months & months, nearly a year......but it only started overboosting on the weekend now just gone. Absolutely nothing on the car changed from the day before it was overboosting, to the day it started doing it. I didn't put any fuel in, didn't top up the screenwash, wash it, check the oil.....lol.....literally haven't done anything to it that might've changed something. Strange innit

 

poss lazy boost solenoid try cleaning it????

 

you,ve had all that done!! no wonder its overboosting mine did same as soon as centre de cat and panel fillter was fitted (standard main cat still in place at that time) it was really annoying but only did it 5th gear as it missed its target boost of say 14.5 psi and went up to 17.5 then back down to 13 then back up and so on and so on while foot planted down, i controled it with a dawes device which was good till got more mods then a re map now its fine the more air flow thrugh intake/zaust the mlore boost and standard map cant keep up with it all (your car should have a 2 port boost valve so if was blocked or ewt it would not boost as air would go strieght to the actuator unlike 3 ports)

 

Get it remapped urgently before you kill it.

Overboost like that IS a serious problem and on a std car that has not been mapped for that level of boost is a ticking time bomb of an engine rebuild.

 

should add overboost can kill an engine in a split second before you can react to it. by overboost it means its producing too much pressure from the turbo, too much pressure in the cylinder and you are playing catch the conrod/piston in the worst case

 

Surprised you haven't hit 'fuel cut' yet - would imagined that to be around 16 or 17psi for a classic?
I suffered overboost when I had the STi Ver III - cured with Blitz boostcontroller set just below fuel cut (around 18/19psi from what I remember)
If it is overboosting and not being protected by fuel cut I guess this could be dangerous - I am no expert though..sorry.

 

fuel cut dosnt realy work in this case as the boost valve open actuator and stays open till it drops to say12 psi then closes and back up again so and so fourth its not being held over 17.5 psi long enough which will cause cut to kick in but that even takes maybe 2 seconds to recognise its at that as i found out when playing with the dawes device, just set it to 16 and it was fine till re map

 

The boost should peak briefly at about 15PSI and settle back to 13PSI in an unmodified MY00 UK car. 20PSI would cause fuel cut and at any rate you would most definitely feel the extra 'go' from that level of boost increase. If the car drives pretty much as before I would suspect your boost gauge is faulty (I've had a VDO one do this, my car is set to run 20PSI and the gauge said I was getting 26PSI). Connect another gauge to be sure before you start worrying, fuel cut will protect you from disaster if the car has been well maintained (i.e. isn't held together by gaffer tape).
Kevin

If another gauge also indicates similar peak boost, I would clean the boost solenoid

 

Cheers for that Kev. I had thought it might be the gauge yeah, but haven't got another one here to try. The car didn't feel any different to drive from the day before it was over boosting to when it was actually over boosting......but obviously it did feel different to drive after I changed the exhaust etc. But it hasn't always overboosted since then. It only really does it aswell when I put my foot right down and I'm at low revs (2k for example) so the turbo has to build right up I spoze. Whereas if I've already got my foot down a bit and am at say 4k rpm and then I floor it.....it doesn't really do it.

Cheers for your answers so far guys