Taking between 5 and 20 minutes before start up chime.
When it's running - everything seems fine, but my Mac Pro takes an age to do the self test, sometimes it doesn't start at all after 10 - 15 minutes.
Sometimes there will be a long wait - followed by the case fan ramping up to full RPM (alarming) then the start up chime and a normal boot.
I've stripped the mac down removing all third party bits, replaced updated graphics card with the original, tried the stock ram (completely different set), disconnected all hard drives and PCIe cards.
I made an apple hardware diagnostics USB stick for this model. It froze a couple of times on the initial hardware probe but passed with no errors twice, but the start up issue still persists.
I restored the upgraded RAM, GPU, SSD etc, and the behaviour didn't change, however AHD did pick up on a PCIe temp sensor error - on researching this it seems this is a false lead and simply due to my third party GPU sending back unexpected readings. Other people with the same GPU get the same error and their systems are fine.
Done NV Ram reset, SMC reset, Logic board battery replacment.
So I've got a Mac Pro that can take 10 minutes plus to get to the point where there's a start up chime, but once it's running, there appears to be no issues. It makes me nervous though because there is obviously some issue there, probably with the firmware or hardware and I find it difficult to get on with work knowing that there's a problem which may start manifesting in other ways.
I had the CPU's upgraded to 2 x 6 core 3.46. Originally this machine was 2 x 6 core 2.93.
Has anyone got any ideas?
Is this a good question?