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Posted 2/8/2018 21:51 (#6564700 - in reply to #6564333)
Subject: RE: 3116 CAT fuel issue

Between Omaha and Des Moines, 7 miles South of I80

John.jr - 2/8/2018 19:50 Working on a 3116 in a Chevy topkick. The truck is hard starting and low on power. The filter on the suction side is only half full. Pressure side is full. With a clear hose on suction and return the suction side has bubbles present at mid to high throttle. Bubbles are maybe 1/16" 1-2 inches apart. Return side has thousands of tiny bubbles at low to mid throttle, clears at high throttle. What's everyone's thoughts? Bad injector cup? Plastic supply lines have been replaced, suction filter was vacuum tested. Cracked pickup tube in tank?

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