[Mk2] [Turbo] Massive overboost but can't diagnose - # solved #

[Olly P]

Yes, it's another overboosting thread

Over the last week my car has had a boost problem. My AVCR is set to 1.0bar and has had the same setting for the last year. However, a number of times recently I've put my foot down from about 3000rpm and (like today) it overboosted to anywhere between 1.2 and even 1.37bar

Then ten minutes later, it'll boosts to the set 1.0bar and hold that boost level fine.

When it overboosts, the turbo spools fine, but the car does not accelerate in line with the boost level my AVCR or boost gauge shows - i.e. it feels like the turbo is just spooling freely up to 1.2 or 1.3bar but I'm not going anywhere. The car also feels very 'stodgy' and bunged up when the overboost happens.

I've checked my Forge actuator with a foot pump and it opens fine and holds 15psi. I've checked all my samco hosing, replaced most cable ties and jubilee clips and checked all intercooler and turbo connections.

Can anyone suggest any other possibilities?

[Steve-O 2007]

Dodgy Boost controller Solenoid?

Try turning the boost controller off, if you boost fine with it off then it will be your EBC most likely.

Do you have Filters on the EBC lines? The HKS uses them and when they get dirty it can cause problems

[Olly P]

That's a good idea mate. I'll try boosting it with the AVCR off.
Although I can hear the solenoid 'clicking' as I accelerate so might be ok.

There are some filters throughout my samco hosing, but all seem nice and white still.

[Olly P]

Turns out it doesn't boost properly with the AVCR off either

Boost is very stuttery at times and it overboosted a couple of times.

Any other suggestions?

[JJ]

Turns out it doesn't boost properly with the AVCR off either

Which points to the AVCR solenoid which Steve-0 has suggested. Try just hooking the compressor feed direct to the actuator and should hold minimum boost. If that resolves it, you've found your problem.

Boost controller solenoids can gunge up... brake cleaner or some degreasing solvent will help rectify it. My engine started boosting low one day, didn't matter what adjustments I made to the Blitz DSBC .. fired some cleaner through it... dried it off .. and bingo.. 100% effective again !

[Olly P]

Ah, ok I understand.

Well, I by-passed the solenoid, thus reverting back to stock boost, and the car drove fine on boost for about 15 mins. Then as I pulled out of a side turning in 1st and accelerated hard, the power dipped, the car felt bunged up and eventually overboosted to 1.0bar. Prior to this happening, the car (stock) was only hitting 0.7bar.

From that moment on, the car wouldn't accelerate smoothly.

I checked the turbo, and all looks good. Literally no shaft movement.

This is getting to me now

[TubbyTwo]

agree about the solenoid mate,

my greddy profec B did exactly the same. I got a replacement boost solenoid from the usa and its fine.

if it does turn out to be this, Pete at Sbits sells them for around £70 iirc.

[Olly P]

agree about the solenoid mate,

my greddy profec B did exactly the same. I got a replacement boost solenoid from the usa and its fine.

if it does turn out to be this, Pete at Sbits sells them for around £70 iirc.

See my post above mate. Was hoping it was that. But it isn't

[MR2_RICH]

I had this last night and I only use an mbc.

Same symtoms of boost gauge flies up, audable spooling from the turbo but not really going anywhere. Hit 16psi before I let off the throttle.

I suspect it has nothing to do with ebc on your car.

I'd be interested to hear some further comments on this.

[Steve-O 2007]

I know how you feel, my boost is pi$$ing me off again!!

Sorted the problem out with a new filter on the solenoid and it worked 100% fine then I stupidly set the boost controller up again thinking that the new filter would give a better setup But NO!! Im stuck with boost problems again So now if somethings working I dont fiddle or it will just go wrong

[G-force]

I've got the exact same problem mate. i put my foot down and it moves very lethargically, i get a fuel cut at 5k revs, its very slow. really p155ing me off aswell, but im gonna take some info from this and try remove my blitz ebc.

is the ebc, wiring and solenoid easy to remove? any how-tos? im a n00b :s

[Olly P]

I just rerouted the boost hose coming out of the turbo and into the actuator (and which goes via the EBC solenoid) to go straight to the actuator i.e. no more solenoid in the loop.

[Odin_S]

I have this exact same problem on my rev 3 turbo.

I have a avc-r, i have to set the duty to 22 to stop it from over boosting( if in 3rd and u boot it still doesnt matter and will over boost )

Had Luke and Harry from PW fixing various things on it. We thought the downpipe was fouling or the actuator was finished.

Had these changed still nothing, for safety i always keep an eye on the boost gauge and just half throttle.

[Olly P]

Well, my turbo looks fine, disabled and by-passed the AVCR, downpipe is only a year old and seems fine, one year old Forge actuator which works fine...

so now it's on its way to Rogue (when I ring them tmrw).

[nick_280]

What was the out come Olly?

[Olly P]

It goes in on the 16th. Will report back on about the 20th

[2barGee]

I had an over boost problem with mine a while back, all be it a rev3 but stock turbo still.

I had an induction kit and full system exhaust and i could not turn the boost down from 1.25 bar as much as i tried. I had a chat with a few people and ended up buying a restrictor for the bottom of the down pipe(takes it from a 3" to 2 1/2"), this basically gives the turbo a bit more back pressure and like magic my problem went away

I was told my system was that free flowing it would over boost.

Might help your situation mate.

[bri0905]

I agree with the above. Mine has no boost controll at all, i have an hks induction kit and de cat and if i accellerate (sp) hard from 2500rpm in 5th when the boost comes in it has hit 1.2bar before i let off.

[nick_280]

I know the CT turbos are bad for boost creep due to them being twin entry, but my ST205 had a 3" downpipe from C2 Power and a Mongoose system and it didn't suffer boost creep yet you do hear of it being a big pain in the ar$e.

99% of cars with boost creep seem to run the cheap crappy XS-Power type down pipe, XS-Power must have know these were crap as they did bring out a high quility decat for more money, JeffD has one fitted and rates it.

Just woundered if that was the case here?

Who has the cheap Ebay special down pipes and who has the more expensive downpipe like Berk & the XS-Power expensive one or, err who else makes them?

[justarn]

got the same prob, mine blew a piston! got a new lump but its still gonna overboost, let me know what rogue say plz fella!