996tt not quite boosting as it should

[kyepan]

Hi there,

My 996tt is a bit slow to build boost, and struggles to get up to 0.6 which is what it usually settles at, when it's right it comes on boost like a savage animal.

Previously I had a boost leak which turned out to be a popped off hose on the fuel pressure reg right bank. Made a test rig and pressurised the turbo inlets which revealed the issue.

But i also....

• Changed both the black and white check valves
• Changed all the little rubber elbows on the vac hose i could get to
• Zip tied everything i could reach.
• Changed one of the one way valves, but not the venturie as that checked out okay. 
• Vacuum tested both diverter valves, they held fine.
• Vacuum tested both actuators, they held too. 

However  a year on, and the car is slow to boost and really struggles to get to 0.6 bar.  
So i've now managed to retest down stream of the turbos and it holds pressure fine at 0.5 bar and 1.0bar for over a minute with simply no leaks, not a whisper.

This time i've also done the following.

• The actuators were a bit stiff and creaky, so i gave them a clean off, bit of penetrant, degrease with some brake cleaner, then put some of the correct high temperature grease on the actuator rod joints and around the dowel as it goes into the turbo, they're now moving freely and without any squeaking. 
• The ECU only shows two codes (i have the foxwell that can interrogate the dme), both for my secondary air pump, which  i know is not happy. 
• The tests on both boost solenoids produced a positive result, they clicked away happily in test mode (I assume these are the dreaded n75 cycle valve 996 605 165 00)
• As did the other fuel vaporisation solenoid or whatever it was tested okay too.

I'm currently investing in a little pressure tester to pump up the actuators to 0.5 bar to make sure their cracking at the right point and by the correct amount in mm. 

Is there anything else that i should be looking at? and does anyone know the resistance of these N75 valves so i can test them with a multimeter.

Bearing in mind, no other codes, no CEL, and the MAF is only about 3 years old OEM replacement.

Cheers
J

Edited by kyepan on Monday 15th March 20:33

Edited by kyepan on Monday 15th March 20:34

[kyepan]

Thanks mod for moving!
Cheers
J

[AW10]

Given the relatively low cost I'd chuck an N75 valve at the problem - part number 996 605 155 00.

[IMI A]

There are a plethora of areas boost leaks can occur from. Worn corroded turbos, holed intercoolers, loose gasket, throttle body and or plenum leak etc. I'd advise getting to a specialist indy who sees 996 turbo all the time. Sometimes these leaks only occur after the car is warm to compound matters! Also the car shouldn't feel savage unless remapped so you may also be over boosting at times with one turbo compensating for the other.