Boost pressure lower than it should be

[El Andrew]

Alright brains trust, what do you think? Car has started topping out at about 7 psi. Is tuned for 14 and used to hit that no problems. Also feels a bit lazier coming onto boost.

 

Car is FG with standard turbo. Relevant intake and exhaust mods are 4" X-force dump and high flow cat, Turbosmart BOV, and aftermarket cooler and pipes.

 

Intake looks good, have checked it over for leaks and can't find anything. Car holds 7 psi no worries and accelerates smoothly.

 

Checked exhaust manifolds bolts to the head and to the turbo. Found two that were very slightly loose but made no difference.

 

Turbo looks healthy, no significant shaft play, spins freely and quietly.

 

Have ordered a new wastegate solenoid as they are cheap and my first thought is the thing seems to be running on gate pressure.

 

Other possibilities maybe a leaking BOV (could chuck the factory one in to check) or wastegate spring gone soft?

 

Anything else I should be checking?

 

Haha I checked that a hadn't flashed in my "wheel alignment/car wash" tune

[gaz097]

Wastegate actuator.

Pull the small line off the front housing going to the solenoid and see if it spools again. Caution as it may/will overboost crazy.

Mine popped off on the weekend and was running 30psi for a little while

[El Andrew]

Thanks Gaz. Do you mean the actuator itself on the wastegate, or the solenoid?

[k31th]

Like Gaz said, disconnect the wastegate control and carefully see if it boosts over 7psi. If it does, it's the control or the wastegate. If it doesn't you have a boost leak somewhere between the turbo and throttle (like you were speculating, it could be the BOV).

[El Andrew]

Cheers guys, thanks. I'll try that!

Fingers crossed for the solenoid for ease of repair.

[gaz097]

Also you cat could have collapsed

 

I'm going to retract my first comment, as a failed actuator should overboost not under boost.

Unless it's stuck open or something

[El Andrew]

Thanks for that.

If the solenoid doesn't help and it won't boost higher with the reference line connected, disconnecting the cat and having a peek shouldn't be too hard.

Should confirm too I'm reading the manifold pressure with both a gauge and an OBD2 device, so have eliminated a bad gauge or sensor.

[El Andrew]

Hang on, I think I've confused myself.

If I disconnect the boost reference from the compressor cover, if the wastegate itself is fine, it should just max out at wastegate spring pressure?

That's what it just did, so I think that keeps boost solenoid, boost leak and cat all as possible causes.

[k31th]

if you connect (rather than disconnect) the boost reference from the compressor cover directly to the wastegate itself, it should max out the wastegate spring pressure if the wastegate/flapper is fine.

 

if you have the boost reference disconnected then the car should overboost.

[gaz097]

With the hose off you should have got a massive overboost. You have no pressure going to the actuator to open it up to bleed off the boost.


It won't really solve anything if it still boosted the same (aka low).


If you connect the front housing directly to the wastegate actuator you will have spring pressure.

 

Actually it did rule out the solenoid, as effectively you just set you duty cycle to 100.