996tt not boosting as it should

Hi there, Posted this on rennlist and pistonheads, but no replies as yet after a good few days, realise the PCGB EGM might be occupying minds over the past few day, but thought you friendly lot over here might have some thoughts... would be very grateful for a bit of input. :worship: 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. I've yet to take it for a spin post-lube as i'm central london, so it'll take me a good half hour to get anywhere where i can actually build proper boost and not be doing double or triple the speed limit. :cop: Bearing in mind, no other codes, no CEL, and the MAF is only about 3 years old OEM replacement. Cheers J

Sounds like you've checked most of the usual problem areas, think you've electrically proved the solenoids too otherwise they wouldn't have clicked. One fairly simple check would be to take the inlet hoses off the turbos and make sure you haven't got a sized turbo by giving them a spin and making sure they are nice and free without play! I replaced most of the same parts on mine fairly recently including the no 16 check valve which was very difficult to do without damaging anything. The only fault I found on mine was a small leak on the rear of the venturi. When I first read your thread I thought do the actuators have holes in them as they suffer from corrosion but if they hold a vac can't be that. Maybe worth trying to pump up the actuators from above by removing the small rubber pipe from the n75 valve to make sure they are gas tight. Hopefully it will just be they needed unsticking and you've already fixed it! Mac Mac

Cracked turbo casings not uncommon but difficult to see given where they're located.

Can do both of them, good shout, had the exhaust off in july to do the water pump and checked the impellers exhaust side then! will do so again tho, as thats worth a check and takes no time. On the cracked housing, which one usually goes? exhaust or inlet? i have one of those little bendy mirrors and lights to get up in there if I know where to look. assuming it's exhaust side. Thanks for the replies.

Its the bearing housings that crack, its very hard to see into that space but they can be refurbished for a fraction of replacement cost from Porsche

Who would you recommend sending to if that's the case? (seem to remember ATsomeone being mentioned on here a while back) - this sounds like hybrid upgrade time

Craig at TDI turbos (sorry I don't have a link) is your man. He will do you any flavour of hybrid you want. He's built turbos for me for over 20 years and never had an issue and provides a great service. His mobile number is 07790 684788 just say Darren Jones put you on to him and he'll look after you. I'll see if I can upload a picture of a cracked core to give you some example of what you're looking for. Darren.

There you go, you can see how it's just rotted away and ultimately cracked. Darren

Oh wow... right, i'll get the mirror out today then! thanks for the reply and contact details! Cheers J

can you not hear where its leaking? soapy water and bubbles maybe? have you checked the bosch throttle buterfly to plenum chamber seal? this was leaking on mine after changing everything else that was leaking more :lol: have you preasurised the system post turbos? if this holds then it proves the turbos at fault. my recomendation is GP Turbos scunthorpe for rebuild/hybrid/billet, but i guess it depends where you are located. Let us know how you get on :thumb:

The intake system holds pressure post turbos up to a bar no issues, so we're good there. Firstly i had a look at the middle housing of the turbos, the right side looks crusty AF but no telltale exhaust carbon deposits, left side was fine, so we're good there I think. Today I tested the actuators as per the service manual, using my new fancy pressure / vaccum tester thing, which worked a treat Standard spec is 0.5 bar pressure on the back of the actuator should result in 0.4mm +- 0.5mm of movement in the actuator rod. Getting the DTI setup and clamped upside down on the exhaust wasn't too trickly on the left bank. Left bank read 0.65mm at 0.5 bar initial reading, which means it's opening too much too soon, which would explain the slow boost build, so i've sorted that but it took a good few hours to get the nuts off and actuator rod cleaned up as the nuts were mostly rust. Got it bang on 4mm to spec after adjustment and new nuts. Right bank i had to make up a little extender rod for the DTI out of welding rod, to get the angle right so the DTI read correctly. It shows 0.58mm at 0.5 bar initial reading, so again it's opening too much too soon. But access is limited due to the heat shield so i had to give up for the day, i think it's an actuator off job as then it'll be more easy to get a socket /spanner on. ran out of time, more tomorrow. Either that or exaust studs off, and heatshield off, which should be okay because all the nuts are only 6 months old. Again thanks for the help. Cheers J

Great news, I think you are well on the way to resolving this, my actuator on passenger side just packed in, but unlike you all my nuts etc looked worse than a nut from the Titanic. So 4 months later everything rebuilt or replaced I will shortly be putting the engine back in, I dropped it after struggling for a week. I fitted new turboshaft actuators, absolute bobby dazzlers 👍☺️ Oh and I have re-glued and pinned all 8 water pipes as a precaution and piece of mind 🙄

Excellent work!!!! I'm sure the pipes will need pinning at some point, luckily mine are okay at the moment. (touch wood). So have you got a workshop and lift etc? that would be so handy. Was that a full rebuild? or just turbos and water pipes? Either way looks like you've been busy, do i spy a new water pump, heat shields and a few other goodies? How many hours did the engine take to remove? Test drive this morning, and it's way better already, comes on boost strongly and holds 0.6 bar with no creep or movement, will tackle the other side this afternoon. It's just miles quicker, you can sort of drive it on the turbo now, rather than on the throttle, a bit more like what it should be. For the first part of the drive it seemed to have remedied the hesitation lump at 2k rpm in first gear at light throttle applications i've been chasing for ages. Which i don't completely understand, the car was uber smooth and really easy to drive slowly. My brain is struggling to understand how adjusting the waste gates is going to affect how the car runs at or around idle, it's not like it's the dump valves or something that can affect the air fuel mixture directly. On the nuts, it took 3 hours to remove the remnants of them, titanic is an appropriate phrase, there was very little left of them on left side, they're so exposed. Can i upload images on here as attachments or does it need to be hosted on flickr or photobucket? Cheers J

kyepan Yeah, this all started with a broken actuator :?: Now look what has happened :lol: :lol: I got in touch with Markski tuning, and so now on the way to a Mafless 600/650 hp tune, basically bigger injectors, new plugs and coils, coolant pipe pinning, new hoses, Turbo's 16/24 Billet hybrid wheels by GP Turbo's, all new Turbo oil pipeline as the originals where all welded into place so had to cut, also replace the expansion vessel and fuel filter whilst engine out. Dropping the engine was a couple of hours, but yes I have a shop with rotary Lift and Forktruck 😀👍

That sounds like a fairly future proofed setup! i'm wondering why mafless? does it max out or the pipe around it max out at some air flow or airflow and pressure combination. standard power with an exhaust is fast enough, i can't even imagine what 650hp would be like. That's nearly 450hp per tonne. Love the prodigious use of the fork lift!!!! I have to change one oil pipe as it's weeping, it's the right bank return from the turbo sump to the scavenge pump, hoping that will come out with out needing to be cut, as it's on the cooler end of the turbo away from all the major heat. So were the pipes that needed cutting the ones into the top of the turbo with the check valves on them? I can imagine they become one object with all the heat. if i have to take the actuator off i'm going to be super careful not to sheer the actuator retaining bolts, time for an outing for the other new tool in the box, a low torque vibrating impact gun for removing stuck glow plugs. it does 10-20-30-40nm and seems to be a bit of a wizz at getting stuck stuff like bleed screws undone without sheering them off. Watch this space. I really think at some point, every 996tt will need to come out and have some major works, the access because of the packaging just makes engine out a much simpler alternative, then you can also inspect everything. One day, when i have a 2 post lift and garage, i'll do mine, and swap the turbos, probably just for some standard k24 hybrids, and a remap, and as you've done, do all the pinning at the same time. Cheers J