I recently spoke with a guy who has worked for ford, strictly on diesel pickups for 20+ years. He told me this:
The buzz test is accurate, however, the cylinder contribution test has been faulty since day 1, and so far nobody has built a scanner that makes it accurate.
I found that hard to believe, so I did a CCT. Well, number 3 failed. So, because I had it apart anyway, we swapped the IDM. Did another CCT. This time #2 failed. So we swapped in ANOTHER IDM, and this time #6 failed.
However, all three IDM's passed the buzz test. And the truck wasn't missing with any of the three. ( It had other issues )
Just food for thought