low max boost problem

Hey guys.I have a boost gremlin for a long time and cant find the problem and i'm about to give up. I have a v70 b5204t3 m4.4.I bought a mbc.after playing a bit i noticed that it doesnt boost more then 0,8bar.i popped the vacuum hose from the wastegate off and still the same.0,8bar max.boost doesnt drop after reaching 0,8b.its just stays there..i talked to some guys with the same engine and the same 16t turbo,they boost up to 1,4bar.soo i started to look for problem.no vacuum leaks.tested like 10 times.cut open the cat converter,looks like new.wg actuator is fully closed,not leaking,sticky or whatever.bought a new turbo chra,changed the exhaust housing cuz it had a crack around wg flap,changed wg actuator.,then is started to boost about 0,1 more but still nothing close to 1,4bar....found a crack in exhaust manifold.changed it.didnt help.car runs fine,no engine checks.did a compression test.all cylinders were 175-180psi.i have no idea what else could cause this.i'm starting to think that everything is ok and i'm looking for non existent problem.any ideas?

How is the intake piping? Maybe you have a restriction on the intake side? Also common to have a clogged cat causing this but if it is ok then I'd look to the intake. Maybe you have a leaking hose that you haven't discovered?

Waaaay back when I was using a 16T on mine, I was running it considerably higher than stock boost, and it helped to add an external spring on the WG actuator. There's a fair amount of force trying to push it open, the higher the boost, the higher the pressure on the turbine side needs to be to make the boost, at some point, it's able to push the WG valve open a little bit even if the actuator has no pressure at all in it.

The more sophisticated WG actuators have air lines going to both side, one to help hold it shut (in addition to the spring), the other to pull it open. An external spring was just a cheap bandaid made from parts laying around the place.

Have you done a boost leak test? (pressurized the intake system and sprayed soapy water on all the charge piping and vacuum connections)

You may be surprised what you find.

today i ziptied wg lever so it wont be able to move at any cause and that turbo spinned like crazy,half a sec and it was 1,2bar and it wasnt about to stop.problem solved.huge thanks JohnMc.

Yeah... be careful with that or you'll get to see your connecting rods.

akaunc said:

today i ziptied wg lever so it wont be able to move at any cause and that turbo spinned like crazy,half a sec and it was 1,2bar and it wasnt about to stop.problem solved.huge thanks JohnMc.

Click to expand...

^^ this is not a fix.
The engine needs boostcontrol, not run-away-boost.

Did you verify if the boost solenoid valve actually works? I think it's mounted near or next to the airbox.


When i had my 2001 V70 T5 this solenoid on my car was mechanically stuck while still electrically OK. I used WD40 to get it unstuck. The lines that are connected to it need to be in good condition and tightly(!) clamped to the right port!



If they are not connected to the right port the turbo is not regulated by the engine management but only regulated to the low mechanical level defined by the spring inside the WGA.

He unhooked the WG line and still didn't get more boost. Boost control wouldn't work in that situation, all it can do is (at the extreme) simulate an unhooked WG line.

The actuator just needs to hold the WG closed with more force.

i'm not going to drive around with a zip tie on wg lol.i should have another actuator somewhere...if changing it wont help, i'll try to add an extra spring on it or something