What causes boost spiking/free boosting ?

[slystiguy]

I've noticed every so often the sti will randomly free boost. Mainly noticed when the cars been running for 20mins or so (around the hills or on the highways). I notice it most in 3rd gear onwards. Probably worth noting I have a leak in my headers atm. Its really annoying when your not expecting it to happen while passing someone an it randomly hits boost/fuel cut. I can only imagine the unneeded stress this puts on the engine.

Wondering where I should start looking.

The car is pretty much stock standard v3 sti. Runs a vf24 with free flowing exhaust and after market headers. Some crappy boost gauge been installed by previous owner.

[Wiretap]

Faulty boost control solenoid, faulty MAP sensor or a sticky wastegate could all be at fault. Your exhaust will also cause some spiking as the factory boost control system isn't expecting it.

[Stoffa]

split vacuum hose on boost solenoid/turbo/wastegate actuator

[Firenza]

Mines doing the same, Im about to take all the boost hoses off, make sure they arnt gunked up / knackered, and that the boost pill isnt full of crap. From what I've been told its quite likely, as Subarus tend to produce a fair amount of blow by which leads to them needing replacement.

If that doesnt fix it, then I'll have to check the actuator, which I havent a clue how to do, so shall follow this with much interest

[Guest]

Had this issue before. Wasn't happy with the rs at all at the time >=( check all your vac lines are nice and afm is clean. Use the maf cleaner it works wonders then I'd check plugs and coils. Try running wastegate pressure and see how it responds, that will give you an indication on your solenoid status

Cheers Muhammad

[subieboy]

Sam face it your car just hates you man.

Seriously,

Check hoses, etc

[slystiguy]

Lies! Cars been going good. A minor exhaust leak and a boost spike here and there is really nothing compared to my last cars and the cortina

[subieboy]

 slystiguy said:

Lies! Cars been going good. A minor exhaust leak and a boost spike here and there is really nothing compared to my last cars and the cortina

Hahahahah easy to wind up

There will be a reaon, it may get worse now winter is here, colder air is more dense therefore it will spike with your setup. try an aftermarket boost controller once you have checked for cracked/damaged hoses/pipes etc

[slystiguy]

hmmmmm was thinking about getting one anyways Not sure on what to look at buying. I really gota sort the adjustys, rear arm kit, sway bars and rear strut brace installed first and then move onto other upgrades. Not to mention the leaking headers,boost spiking an ticking rear cv. Fuck this is going to cost a shitload by the time I actually get it sorted. But it will be a wicked ride haha

[subieboy]

A lot of that stuff you could do yourself (may need a hand with some)

Sort the boost first, if you blow the motor then that will be $3K+ thanks for coming...

The other stuff can be done at home or with mates help.

[subieboy]

See Louis next door at Slade engineering for the headers (he may weld for next to feck all)

OR see magoo for the headers...

[slystiguy]

Yea will pop next door when I get them off this weekend. I plan on bare metaling them and get any leaks done hen heat painted an heat wrapping them. If I can do the sway bar I will be happy the rest I sorta want done by a pro so its setup all perfectly. handling and all want it to be trucking perfect

[WRXONP]

a leak pre turbo will only be causing lower boost - not higher boost

the only way u can get free boost is the fact the wastegate is staying shut so it can only be

sticking boost solenoid (clean or replace)

leak in vac hoses causing gate to stay shut

blocked pil or blocked hose

wastegate flap is stiff / jamming

actuator is stuffed (leaking)

the fact its only hitting cut in higher gears is because the engine is under more load in higher gears

a leak on the map sensor line would actually cause the opposite - depending how much its leaking it would actually raise the boost cut higher (not lower)

whats it over boost to when u hit the cut?

[slystiguy]

gets to about 22psi I think. Not sure how accurate the gauge is. I'll have a good look over it this weekend and let you know any finds

[WRXONP]

if ya cant find anything wrong with the plumbing side of it (vac hoses) i know on the older models (ver 1-2 / bc5 etc) when u plug the check engine connectors under the dash together and turn key on the solenoid cycles - pretty sure everytime i turned my ver 3 key on (no plugs) the solenoid cycled - anywho if it doesnt cycle its more than likely stuck - if it is cycling - run brake clean through it whilest it cycles

realistically u could put 12v accross it (unplugged from loom) and it should click and when power is taken away it should also click

if no clicky clicky with power straight on it then its poos

if everything along the lines of vacuum is fine - then pop the circlip off the internal and feel the internal (not the actuator) it should move back and forth very freely - if its tight to move then thats the problem

you can also test actuator with a compressor - put air gun onto nipple and pump and it should push the wastegate open

[WRXONP]

trying to think back - if i remember corectly my ver 3 boost solenoid would cycle when the TPS came off the idle contacts - atleast im pretty sure - someone on here would be able to back this up if what i remember is right or not

[slystiguy]

so found the exhaust leak.between the header/upppipe connection. Gasket was abit munted so took it out put stock headers on and filled it with maniseal for the temp fix until I can get a new gasket.Boost comes on alot quicker now. 3500 and shes pulling

Didn't find any vacuum leaks but I reckon I can hear it so its possibly there somewhere. Can you spray something on the hoses to find it? Or if in doubt should I just replace the lot with new hoses? if so what diameter should I use?

Random question but... when putting my stock headers back onto my aftermarket uppipe I noticed the internal diameter of the uppipe is like 10mm larger than the headers internal! wtf? Wouldn't this be giving me huge lagg on a vf24? and probably better top end? Is it worth changing back to a stock uppipe seem as its only a vf24 an not running modded boost? is there any advantage to running After market headers with a larger bore uppipe on a vf24?

Also noticed headers are 4-1 unequal stainless jobys. Any good or should I trademe them an get some equal 4-2-1?

[WRXONP]

Easiest way to check vacuum lines for leaks is jut pull them off and visually inspect - after old age they go brittle and crack

But seriously take the lines off and blow through them too could be blocked with oil and gunk -

I'm picking it's a solenoid issue - either not cycling or blocked

And as for the headers - I ran stock manifold and a over sized up pipe like u have - changed it back to stock - had allot more mid range - top end wasn't even effected with proof by dyno sheet lol

I ran the stock manifold and up pipe upto 235 kw atw - and I'm sure it would easily do more too

[Stoffa]

where did the rest of the gasket go? hope it wasn't through your turbine

[slystiguy]

Didn't see it drop out lol. Wondered the same thing. Could have blown out into engine bay though?>

Many thanks for the input fellas Gives me abit more direction of where I'm going to go with this car.

also found this today