I had the Precise Flight in my Super Viking... We got into a situation
where the engine would suddenly go lean, pinning the EGT, causing me to
have to quickly go full rich (once I noticed), reduce throttle, then
reset and relean, or it would suddenly be running way rich making me
crazy... This came to a head after multiple episodes over 7 months with
the spending of thousands of dollars on multiple mechanics who couldn't
find anything wrong, and replacing the fuel injection pump ($0.7 AMU),
injectors, etc... Finally, it happened twice on a local flight and I
lost it mentally, landed, grabbed my wrenches, and began stripping
down the induction and fuel system.. Took me all of 25 minutes to find
it... The pivot pin on the flapper that selected between suction from
the pump or suction from the intake manifold had come out... The pin
and a ball bearing were gone, sucked through the engine... The flapper
was rattling around in the TEE valve and it would randomly block or
unblock the orifice to the intake, radically changing the mixture...

Precise Flight made sympathy noises and offered new parts at no cost
(and would I send in the old ones - didn't want the FAA seeing them)...
Of course, they had no interest in reimbursing me my costs... While I
replaced the defective parts I have no interest in having their sytem
on any planes in the future...

denny