Q: Install Sierra on Early 2009 Mac Pro

It won't work on a 2009, you must have a 2010 or later. While I not sure exactly why Apple did that but there I know of no way around it, and if one does indeed exist it would be a process that can not be discussed on this forum with the TOS we agreed to.

It can be done. I have installed macOS Sierra on my old iMac (2009) and it works just fine! Specially after updating the HDD with an SSD. You will need to create a patched installer and for updates you need to use a special update checker. Both freeware tools can be found here.

Just update the firmware on the 4.1 to that of the 5.1

http://arstechnica.com/apple/2011/05/firmware-hack-can-transform-a-2009-mac-pro- into-a-12-core-monster/

Apple have doth decreed that the Mac Pro 2009 is BS - Before Sierra and therefore unclean . Thou must join the heathen masses in purgatory running El Capitan for ever more.

See - How to get macOS Sierra - Apple Support

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The reality is that Apple has almost always deliberately killed off support for older models after a certain amount of time. Sometimes this is for legitimate technical reasons due to older models not being able to support certain new features, e.g. AirPlay using the hardware encoding feature of newer Intel chips, sometimes it is purely down to Apple no longer being willing to support relatively old models in a desire to force the advancement of the Mac for the benefit of users and developers, this contrasts with for the most part the Windows world which as a result is still wilfully using Windows XP on many systems. In this case the Mac Pro 2009 is not a totally logical choice in that from a technical point of view it is not different in any noticeable way to a Mac Pro 2010 which is PS - Post Sierra and therefore clean In fact as Illaass pointed out you can unofficially upgrade the firmware of a Mac Pro 2009 to the same firmware as in a Mac Pro 2010 and then Sierra is perfectly happy. So for the list of Clean/Unclean Macs models as per the above Apple article some will probably be disallowed due to technical reasons, some due to mere age like the Mac Pro 2009.

I own 2nd hand "early 2009" MacPro. However, it surely has been upgraded by the seller, since its firmware is 5.1 instead of 4.1.

Anyway, Sierra installed just fine. It's only that the wi-fi card (Airport extreme) is not recognised anymore and should be replaced by a more recent one.

This is the problem I have. I have Sierra installed on my Mac Pro 5,1 but the airport card does not work. The menu bar says "Wi-Fi: No hardware installed"

Do I need a new wifi card? This is the one I installed in it : https://www.amazon.com/gp/product/B0012YYITW/ref=oh_aui_detailpage_o04_s00?ie=UT F8&psc=1

Thanks

Correct. The image of that card shows that it is a BCM4321 with is not compatible with Sierra./

This one is compatible with Sierra

https://eshop.macsales.com/item/Apple/BCM94322MCK/

There is also this card. It supports the AC wifi band and incorporates bluetooth 4.0

http://www.osxwifi.com/apple-broadcom-bcm94360cd-802-11-a-b-g-n-ac-bluetooth-4-0 -with-adapter-for-macpro-2008-2007-2006

Thanks!