Did you happen to take a fuel pressure reading? (cranking, at idle and at high idle)

First, I will ask you to check and see if there is a "Fuel inlet screen" on the short inlet tube, to the CAT transfer pump. (Note: Not all 3116 have this screen) See pictures(copied from my earlier threads).

Your pictures, look fine for the fuel supply hose (I assume you had engine running during photo)

Were you sucking fuel, from a bucket, on TOP photo?

I'm not too excited, yet, on those return lines, to condemn anything major; like a copper sleeve issue, BUT remember that can be totally different if engine was under a load (like on a chassis dyno)

Have you pulled the valve cover, yet? {= looked for some rack bar movement, the instant someone turns ON the ignition key = if you don't see any, then also watch while cranking the engine, for 10 seconds too}

These engines prefer to have some fuel pressure, to start the engine while cranking, BUT as injectors get older and really worn, they will be hard to start also, even with a little fuel pressure during cranking. (You didn't mention overall miles, on truck) in those cases, it requires new injectors (but that is last resort)

There are too many things that add up to hard starting and low power, and I'm not going to write a novel, on here, either.

Sticking rack for injectors,

worn injectors,

poor governor spring preload,

dashpot allen screw fell out,

lack of oil to governor

Blown air/fuel ratio diaphragm

Improper low idle rpms,

sucking air in fuel system

combustion gases, getting pass injector sleeve/coppers

restriction in fuel supply

fuel setting adjustment incorrect = looks like someone has changed Fuel Governor = So did they measure and adjust "Full Load" setting ? (reference point for governor housing to #1 injector) OR did they just throw it on and ASSUME it would be OK???

etc. etc. etc.

Air filter problems, air to air cooler problems

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(3116 fuel inlet screen with debris_hf213.jpg)

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3116 fuel inlet screen with debris_hf213.jpg (57KB - 433 downloads)

Here's a picture for fuel pressure port.

Low idle should be closer to 750-800 rpms. (this adjustment will also provide a slightly more governor spring tension, during cranking) = helps move the rack bar in the "fuel ON" position, when ignition key is turned ON.

Don't worry about a video, once a person confirms fuel pressure, set low idle closer to 750-780 rpms, retest/restart/crank, and if necessary, pull valve cover and watch rack movement(as mentioned earlier), and even take long screwdriver (while engine is running, at idle) and move each individual injector's fuel rack, to the "fuel ON" position (causing a fuel knock) then watch return sight glass/hose for extreme bubbles.

Is this hard starting, only a problem once EACH morning, or EACH time the person cranks the engine; hot or cold?

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Rpms look fine, Fuel pressure seems fine, too

note: You know that you may have already "cured" a low power complaint, with new fuel lines and new filters and new fuel check valves; because you didn't have any fuel pressure reading, Beforehand, to compare to.

You haven't mentioned "How long" does it actually take to start. (5 seconds cranking, 10 seconds or 30 seconds)

Also, was/is the hard starting, just in the mornings? or EACH time a person cranks the engine? {if problem was only each Morning, then You may want to inspect the fuel return check valve, also}

If it does take a long 30 seconds, of cranking; have you removed Air-to-Air tube and just tried a very quick squirt of ether, just to see how quickly it might start running?(might be a clue, to worn injectors, when those engine start very quickly with just a touch of ether, BUT normally we have tested and readjusted every adjustment and any another possibilities, before condemning a set of injectors) = basically only when you total believe you have everything "perfect" and it still takes 20-30 seconds of cranking OR a quick shot of ether(to be able to start quickly), do we finally commit to installing a complete set of injectors.

How do those clear fuel hoses "look" when you first start/crank the engine? Big bubbles anywhere?

note: there are areas, that we having even talked about yet, such as injector timing, valve adjustments, injector synchronization, governor inspection, "Full Load" setting, testing air/fuel ratio control., etc.

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Here a guy testing the Air/Fuel ratio control valve for leaks on its internal diaphragm. (causes low power, if blown)

(I didn't read it, but it will give you pictures, for testing)

Testing can be done with governor, still on the engine

 http://schoolbusmechanic.blogspot.com/2009/07/cat-3116-troubleshooting-no-power.html

Looks normal, for an engine without any load on it.

Just FYI: For viewing sight glasses properly, you need to position fuel line/clear tube and watch the fuel "going uphill" in those lines. {Don't be fooled by any stagnant air bubbles sitting in some horizontal piece or downward piece of clear hose.}

Your hoses aren't too bad; personally,I would have made them a little longer, just to get some more area of "Vertical flow" to view.

 On longer hoses, we will lift the hose, to remove any stagnant air bubbles, right before testing, then lay down how we want, for viewing and then test, from there.

Here's a diagram, of what CAT puts in there literature, for one of the sight glasses that they sell:

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sightglassviews.jpg (67KB - 344 downloads)

During next start-up, see if you can watch your sight glasses/hoses carefully = might need 2 people = one to turn ignition key, and you to watch the clear fuel hoses.

Also, record if there was any fuel, at all in that clear SUPPLY line/fuel, even before cranking (or did it "drain backwards", over night)

Note: Looking to determine if any "air" is coming from supply line, or is it coming from injector area or maybe the whole fuel system drained backwards