I am not able to find the Farymann P30 Diesel Repair Manual (marine engine)

Ask them direct, it sounds like some sort of Protection Mode.

Cat 3512 engine
Overview. For your largest power needs in any environment, Cat® 3512 Industrial Diesel Engines offer the unsurpassed performance and durability your customers need to keep their industrial applications and operations running. They deliver high power output, proven reliability and excellent fuel efficiency.

3512 Industrial Diesel Engines ' Cat ' Caterpillar

and

https://www.google.com/search?q=cat-3512+engine+%27incorrect+ECS+switch+input+reduce+power+now%27

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Question edited for clarity, 'year make model (what it is)'.
Question moved from Motorcycles to out only Volvo Penta cat.

Volvo Penta 3.0 GL GS cylinder head Bolt Tightening Torques

Volvo Penta 3.0 GL GS Cylinder Head Bolts
Step 1 = 47 Nm, 35 lb.ft
Step 2 = 88 Nm, 65 lb.ft
Step 2 = 122 Nm, 90 lb.ft

Repair manuals. They are seldom free!

https://www.google.com/search?q=2004+VOLVO+PENTA+MARINE+ENGINE+3.0+LITER+repair+manual

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Nowhere, Service manuals are several hundred pages. If you own the engine then you need to purchase the manual.

https://marine.cummins.com/marine/public/productListingAjax.action?friendlyUrl=/Auxiliary/6B

I hope this helps!

he main manufacturers of diesel engines for boats: Caterpillar Marine, Cummins Mercruiser, Detroit Diesel, John Deere, MAN, Westerbeke, Mecruiser Diesel, John Deere, Volvo Penta, and Yanmar.

For more information on these manufactures, check out these websites: http://marinefuel.com/marine-engine-manufacturers-diesel/ and http://www.discoverboating.com/buying/types/engines.aspx?id=80

Did you loosen an injector line to see if you are getting fuel to the cylinder? Did you bleed the filter when you changed it? Was the rebuilt pump properly timed when it was installed? Are you sure all the air was bled out of the system after the pump and filter were changed? Do you have air bubbles in the fuel return line?
A copy of Haynes Diesel Engine Repair Manual, part #10330 ($20) could prove to be invaluable to help you track this down. It has excellent coverage of GM 6.2 and 6.5 engines. Hope this helps.

Check out faxonautoliterature. They list an original Ford wiring diagram manual for your truck for $59. They also have a couple of different Ford service manuals for your engine, diagnostics and repair. If your wiring and relay problems are engine specific then a copy of Haynes Diesel Engine Repair Manual, part # 10330, will be right up your ally. For $20 it provides an excellent trouble shooting and repair manual for the DIY diesel owner. It has separate sectons for the 6.9 and 7.3 engines as well as GM. I know this isn't free but I hope it will help.

I owned one diesel engine. I would say the engine siphoned the diesel after it was shut off.
The throttle controls may not be closed. The injectors were tested for their opening and spraying, but were they tested for closing and sealing when off? Diesel fuel lines maintain a vacuum or they get air bubbles. Cooling cylinders create a draw right into the crankcase. Last idea-crankcase vent clogged