Service manual 33 is what I think you need.......Maybe someone can give you a link for it.
Pm me (personal message) with you email and I can try to send you the PDF manual. it is ~ 7 MB in size.
From what I read, and I do NOT have any experience with EFI so.........
The code 19 does not seem to refer to any sensor failure.it refers to things like a spun hub in the prop, over rev in neutral, cavatation, thus allowing over rev condition thus code 9 (guardian mode).
That being said. You say it will not go above 4200 before this happens.........
Have you reset the codes?
Maybe disconect the battery for a minute or two and reconnect. Let everything reset.
One issue I have seen reported here is bad contacts on the engine harness connectors....Pull them apart and look close for corroded contacts (pins and sockets). A weak signal froma weak contact could cause a wrong reading with respect to you rpms......
Maybe use a small amount of dielctric grease on the connectors and reseat all of them.....
There are only a couple of guys here that have any real EFI experience.........Maybe they will chime in and give you a better answer......
FROM MANUAL;
One thing in the manual says:
Continuous horn and 5-90% available power:
Battery voltage,
Guardian strategy,
over speed,
ECT over heat,
ECM memory,
Multiple CAN circuit faults,
EMCT over heat
This one looks interesting..
DTS SENSOR FAILURE..................5% Available power
Last one is :
Engine oil pressure......Forced idle