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El Andrew

Boost pressure lower than it should be

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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

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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

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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).

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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

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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.

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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.

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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.

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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.

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Ah yes of course, I was getting confused with connecting the compressor cover directly to the wastegate.

Hmmmm so I guess I'm maybe looking at either an exhaust issue or a boost leak.

I've swapped the factory BOV valve in for the drive to work tomorrow - probably done enough driving around the neighbourhood like a knob for one night.

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No change with factory BOV so wasn't that. Rechecked for loose intercooler pipes and everything is perfect.

Removed the cat and I can see through it, so it isn't that so am a bit stumped.

Could it be a collapsed muffler? Have always thought the exhaust sounds pretty spluttery.

Might investigate if the wastegate is stuck open too. I've got a good exhaust guy so will have a chat to him too.

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when you're looking through the cat, does it look like a honeycomb/lattice all the way through? or does it look like a big open space?

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Just thought to check the air filter. Was pretty filthy which I'm putting down to the weeks of smoke we had here. Only cleaned it 5k ago. Had a new Ryco paper filter lying around so chucked it in.

Didn't make a difference.

Did happen to be on a private road where I got stuck at a series of red lights, so could do some decent pulls. Will spike to10 psi and then drop as the revs rise. Exhaust actually sounded quite bad - not sure if that is the issue or just a symptom so will definitely get that checked next.

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does still sound like a boost leak, then... e.g. it's sealing pretty well until the 9-10psi mark then it blows the opening open a little more and most of your boost leaks out as you go into higher revs.

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Went to the exhaust shop today and exhaust is fine. Couldn't find any other issues with the car and thinks there is a good chance the wastegate is cracked. Not sure if that means the flap or the turbine housing around it.

Is going back next week so he can pull the dump off and have a look.

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Exhaust place put an inspection camera through the exhaust and removed the dump, checked the wastegate, turbine housing, turbo bearings and exhaust manifold. Also checked what they could in terms of intercooler pipe leaks. Didn't find any issues.

I think I might try to make something up to pressure test, or get tested, my intake system.

Just a question on the wastegate test - if I'm disconnecting the line from the compressor housing so there is no boost reference to the wastegate, wouldn't that create a massive boost leak anyway?

Given I bought a new solenoid, I might just fit it anyway.

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if you disconnect the line from the compressor housing to the wastegate, it'll overboost (if the system post-turbo isn't leaking out the extra boost created) and the turbo will boost as high as the mechanical pressure in the wastegate allows.

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So basically the turbo, with the wastegate shut, is able to overcome the boost leaking out of the fitting in the compressor cover?

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I don't think a reasonable volume of air would leak out of that tiny fitting, compared to how much volume of air the compressor wheel is moving out of it's outlet, so yes, it would overcome it.

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Made up a thing and leak tested pressurised the intake system.

There's some hissing down in the front bar. Past Andrew left the hose clamps facing forwards, so I could get a socket through the grill and tighten but it didn't help. Think I'll have to remove the front bar and reposition some of the silicone joiners. At least I found something though!d0a9d51cb2822c7651277a10fb73ab21.jpg

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