I had issues with 'Surging' and overboosting on my stock K16 996TT - it would boost to 1.3 bar on occasions but mostly 0.9 or 1.0. It then dropped into the 'default ECU map' due to overboost errors and started to run like a bag of spanners (lumpy/jerky at low throttle)

I read up on the overboost and tracked it down to N75 or MAF, tried the MAF and it wasn't that so onto the N75. Swapped it and all is fixed - boosting solidly to 0.6

I then disconnected the battery for 10 mins to clear the codes and get the car back to the proper ECU map. The car is so smooth to drive now in addition to the boost being fixed.

I didn't find any DIY's for this and its fairly straightforward having done it so I thought I'd drop a few pictures and a 'How to' down here to maybe help and guide others.

Step one
Remove airbox by removing MAF plug and taking out main retaining bolt near boot release then undoing jubilee clip.
Twist airbox anticlockwise as you remove.
Step two
Undo intercooler pipes as shown below by sliding out the clips.

Step three
Remove all pipes and connectors attached to the 'Y' manifold carefully and push out of the way. (NB - Picture below shows airbox which would be removed by now)

Step four
Undo jubilee clip at top of 'Y' manifold just before the throttle body as shown below (Stumpy screw driver or socket set required here)

Step five
Gently wiggle and twist 'Y' manifold - it will pop off. You only need to move manifold to the left half an inch or so once removed to get access to N75 valve - it remains attached in place. You will now see the N75 valve as below

Step six
Slide off the 3 x pipes attached to the N75 valve
Sldie the valve off its mounting and lift it out a little
Unplug the connector below after removing the metal retaining clip

Step seven
Reverse the above process
The only tricky bit is getting the pipes back on to the N75 valve - you really need a pair of these or its a PITA to do.
The bottom pipe needs to be pushed on using the pliers through this gap (it will make sense when you do it)


Step eight
Have a REALLY good check over to make sure you have reattached everything correctly and no snags or rubs exist.
Step nine
Disconnect battery for 10 mins to clear any fault codes from before the fix (turn ignition on if UK car to avoid alarm before disconnecting battery) - ensure you have radio & nav codes in advance.

Here's the old and new N75 side by side:


P/N of N75 is 996.605.155.00 cost of part is about £20!

I would allow 2hrs for the first time you do this and prob 45 mins if you needed to do it again.

Disclaimer - In line with common sence, this DIY is entirely at your risk, no guarantee of a fix is given or implied!

Cheers,

Jim

 

rep points for that for sure ....... thanks jim.

 

Nice write-up, and a job well-done!

Oh, and a +1 for your efforts

 

Nice write up. Also if this doesn't help make sure your wastegates aren't sticking.

 

Very nice info, rep point for you Thanks a lot!

Just want to share the info I just found about the function of the N75 valves....http://s4wiki.com/wiki/Wastegate_bypass_regulator_valve

 

Hi, where did you purchase n75 valve for £20?? I think it is worth me doing this as i have the same prob as you, thanks

 

Any Porsche main dealer, part is £16.85 plus VAT - I used the one in Sutton, speak to Nathan in parts 01213785800 If you need any pointers with fitting give me a call/pm and we'll sort something out.
Cheers
Jim

 

Thanks jim ill call them now.

 

thanks for pics, but are you actually removing Y manifold or just loosening it to get under it?? Are you removing huge air filter box too? PLease let me know. I'm about to do this job after changing diverter valves too to fix seemingly low boost pressure. Thanks

 

nice write up. i've replaced mine before as well.

 

Nice DIY

 

Just did mine. This helped. Great DIY thanks!

 

Nice info

 

You did a good job...Thanks..

 

good job. I actually saw this valve, when I removed my y-pipe, but did not know what it did.