22 replies to this topic

[Wadesta]

Hi All,

 

I was hoping to bounce some ideas around regarding some mad boost issues I have at the moment. 

 

Basically, at the moment, I am getting a maximum of 0.8bar of boost on the primary, and a maximum of 0.4bar on the secondary. I have run through a tonne of checks to try and find where the issue could be. The highlight of it all was when I completely disconnected the waste gate line off of the primary turbo. I was able to achieve a maximum of 1bar on the primary and 0.5 on the secondary.

 

I can't find any boost leaks, and I have checked both turbos for acceptable shaft play and free spin. Both are fine. I have blocked off the secondary bypass valve and main by pass valve. Neither of these made a difference. I have also done the UEC through the BBOD trick with no change (didn't expect it to). Done all of the VAC lines as well as the ECV adjustment (however, I will do it again as this is the only thing I can put my finger on at the moment). I have also recently replaced the intake manifold gaskets.

 

I am at a bit of a loss and I am hoping that there are a few peeps here that can throw a couple of ideas out there that I might trigger something in my big beautiful brain that would solve this issue. In the spirit of full disclosure, I do currently have a open circuit on my front O2, however, I would have still expected to see a decent boost spike when I disconnected the primary's waste gate.

 

Cheers guys!

 

Wade

[duncanm]

- Is the ECV ok / opening fully?

- IACV (secondary intake air control valve) opening?

- SPRV (secondary pressure relief valve) shutting ?

 

as you see lower boost in secondary, I'm guessing the SPRV is not shutting off. Try blocking it and see what you get.

[Jimbo]

Have you done the basic checks, such as looking at the ECU for codes?

What are you driving? Might give us some insight.

0.8 on the primary sounds pretty normal to me, at least with stock JDM models. It's the 0.4 on TT that doesn't add up. I'm with Dunc, something isn't holding.

[Wadesta]

Sorry guys, I should have said it's an '02 AUDM B4 Liberty.

Dunc:
ECV is working fine. If I free rev it past 4500, it opens right up. Also works with the connectors connected
IACV is working fine. Again, cycles when the connectors are connected.
Is the secondary pressure relief also known as the secondary bypass? The one that site between the secondary outlets and inlet pipe? If so, then yep, that's all sealing up correctly. I tried blocking it off with no change.

Jumbo:
Have checked for codes with the only code being the open circuit O2.
0.8 is definitely in the realm of what I would call normal, but it's got me beat as to why it won't build back up when it switches to twin turbo mode. I was hoping someone would have had a similar problem.

Thanks for the replies guys! Much appreciated!

[duncanm]

Yeh - I think pressure relief / bypass same thing. That little plastic BOV looking device in a U-shaped loop of hoses, driver's side of TMIC.

 

Sounds like you've checked all the valves.. what about leak testing the secondary pipe between turbo and IACV? Signs of running rich (black smoke) when on secondary would point to a boost leak.

 

Only other thought I have would be constriction in secondary circuit - intake or TMIC connection... like a collapsed intake pipe.

[Wadesta]

I'm pretty confident with all of the valves / solenoids operating correctly. No signs of running rich. Plugs are a good colour and no signs of black smoke.
Haven't done a leak test yet, but it's on the cards.
No restrictions in either the intake or outlet of secondary. I have replaced the outlet hoses of both turbos with silicone. The intake duct looks to be in good condition (checked it all when I did the intake manifold gaskets).

I might look a smoke testing the whole intake system and see if anything arises. The biggest thing that has me beat is the fact that I can only make 1 bar with the wastegate disconnected.

[duncanm]

I see your line of reasoning -- which is why I figured the problem must be a restriction/blockage or leak in the secondary turbo intake system.

 

Unless for some oddball reason the secondary isn't spooling up -- but what could be causing that if you've checked the turbo is free spinning ?

 

The only other thought I've just had: check the condition of your exhaust flexi join - it could have collapsed and blocked the secondary exhaust flow.

 

A big blockage in the combined exhaust (eg: second Cat, if you're running the original exhaust, the exhaust valve thingy) could also be limiting overall boost - maybe run it up the street with no cat back and see how it goes.

[Wadesta]

That's a damn good idea. It has got an aftermarket exhaust, but that's not to say it hasn't done something silly and is causing issues. When I get some spare time, i will give that a go and see what happens. Definitely won't hurt to rule it out.

[LukeFranky]

If you have an O2 code I'd get that fixed first. I chased my tail for over 6 months after installing a knockoff sensor.

[Wadesta]

Yeah, I remember reading that thread in its entirety (and I do mean in its entirety). I am going to change the O2 soon, however, I know that this problem will persist once it is done, so I am trying to pre plan and order any other parts that might fix it at the same time.

[Wadesta]

 

Pretty much what its doing. Sorry about the shakey video....... and breaking all of the laws regarding mobile phones and driving!

[Wadesta]

So I replaced the O2 Sensor, and cleared the code, but as suspected, it didn't fix the boost issue. Decided to pop the intercooler off today out of curiosity and noticed a bit of oil around the shaft for the IACV. So I removed the bolts that hold the vacuum mechanism in place and noticed a fair bit of play in the bearing at the base of the control valve.
 
Just wondering if anyone can tell me if there should be play in that bearing, and if so, how much.
 
Cheers all!
 

Link to image of the oil around the IACV

http://imgur.com/a/8P3lq

[Jimbo]

The intercooler valve shouldn't have much (if any)  play in the actuator arm at all, if that's what you're referring too. 

Under normal primary operation, the valve is held shut via a vacuum, once the conditions are met the vacuum is shut off and then the spring overcomes the arm and it opens.

Even so, it can't really be the problem as the symptoms would be the opposite of what you have. You'd be getting like no boost on primary and then all of it when the secondary got going.

I'm thinking out loud here,

Do you know for fact your secondary turbo spins up? I'm thinking the secondary is seized or maybe damaged impeller/compressor.

If it was seized, you would get all your primary boost but then lose most of it once the ECV opened. Reason being the ECV would then act as a giant wastegate as it's expending energy from the primary to spool the secondary but if the secondary was kaput you're not seeing the extra boost.

The ECV wouldn't "know" the secondary was dead so it will continue to open. But i'm thinking if the secondary didn't make enough boost to reach target with the Differential Pressure Sensor, it would probably throw a code 66 (TT Operation Fault).



 

[Wadesta]

Yeah, I'm confident the secondary is spinning up. I have loosened the dump pipe off of it, driven it into TT operation and she squeals like a pig. Sure sign that it's spinning up. That and there is no code 66 being logged. Impeller and turbine wheel are in good condition. I have visually inspected them, as well as the housing with no signs of bearing failure. There is no end float in the shaft, and nominal side float (to be expected with plain bearing turbos).

The IACV operates correctly. This has been confirmed with the diagnostic connectors. My biggest concern is the amount of engine oil around the shaft of the IACV and the amount of play in the bearing. I am wondering if it's just a nice little boost leak.

[Jimbo]

Amount of oil is normal. TT's tend to build up a fair bit. You can pretty much drain it from the intercooler!

[Wadesta]

Lol, your not wrong there!

[duncanm]

Is the wastegate holding ok?  Maybe the spring has gone.

 

Try tying it shut and going (carefully) for a drive.

[Wadesta]

Wastegate has plenty of spring tension (when moving it by hand) and is sealing well (checked when I removed the dump pipe).

Is there a check valve or similar in the BBOD? How is positive pressure prevented from entering the vac system? (If that makes sense)

[duncanm]

not a bad idea - there's at least one one-way valve in the system -- check the diags.

[Wadesta]

Yeah, I'm wondering if boost is leaking past that check valve and pushing the IACV open. For the sake of $3 odd, I might replace the check valve. I think there is one in the BBOD