Cat 3116 Fuel Issues- help please

[RTSmith]

Hello. Will try and keep this brief. 1997 Chev C-6500 with 3116 Cat and 6Sp. Engine AR#106-7877. 185HP. This is an old flatbed dump on the Christmas Tree farm. No tags, no insurance, never sees the road. And we aren't mechanics. Has started and run great for years. Got low on fuel, and when backing up a hill sputtered and quit. Added fuel. Ran, then quit. Replaced block mounted fuel filter which had rusty bottom to it. Started- idled 15 minutes fine, but quit when started to drive. Found a frame mounted filter by tank that was ancient and full of crap. Replaced it. Removed tank and dumped a ton of sludge out. Filled & reinstalled filters. Started and idled for an hour, and allowed us to rev it up. Head across the field and in 5 minutes quit. The upper filter was 1/2 full or less. We can find no external fuel pump at all. Routing is from tank, to frame filter, to a steel line at back of engine that goes to front of what we think is governor/injection pump. There is a check valve inline going into that, that we removed and checked and it was clean. We are certain that we can get fuel from tank, through bottom filter up to where the rubber line ties into the yellow steel line- if the pump would just suck it. Or is it- but why is the engine mounted filter sucking dry? It shows as a 2 micron- can it have clogged? Ideas please.

 

[Delmer]

Yes, that's the governor/ fuel injection control on the side of the front of the engine. It has a small gear pump that is not good at pumping air, it won't suck fuel from the tank for priming. I've loosened the lines and blown in the tank vent hose to bleed it to start after air gets in.

You have an air leak. Probably a plastic or rubber hose, probably near an end where it flexes the most. Could be a fuel filter seal if the old seal was left in place, the new seal wasn't lubed with a drop of oil/fuel, etc. You could try 5PSI of air pressure on the fuel line from the tank, but a suction leak won't always leak air. You could also add an electric pump between the tank and the first filter.

 

[RTSmith]

Thanks Delmar. But with it idling for an hour, we figured that we'd gotten prime established. Is the block mounted filter (the Cat one so to speak) before or after the fuel pump? I'm not at the truck right now to trace the line.

 

[Delmer]

Yes, you have it primed. I wasn't clear, blowing into the tank is what I've done when it won't start.

You have a suction air leak in one of the places I said most likely. The block filter is pressurized, after the fuel pump, before injectors. Only the lower one would suck air. And only the tank to the first filter to the fuel pump would suck air. That may possibly include the gear pump itself if the seal is bad could suck air? but that's the least likely.

 

[Mobiltech]

The block mounted filter is after the transfer pump which is a piston pump with 3 check valves mounted in the top of the governor. The pressure at the block filter should be about 20 psi at idle and around 50 + at hi idle.
You could have a suction side leak. The plastic supply lines on that vintage have been known to rub through under the drivers door on top of the fuel tank.

 

[RTSmith]

Wanted to update- and a huge Thanks! for the help. Most of the lines were already replaced with rubber, but we replaced them anyway. Found a generic screen/sock for the pickup and swished/flushed the rust out of the tank as well as possible. Still no better. So grabbed a generic low volume low pressure electric pump ($20 on Amazon) and mounted it on tank, pushing fuel into the frame mounted filter. So far so good!!! Of course after this, hyd cylinder on the dump blew out, so I got a 20 mile run @ 55MPH on the road today to the hyd shop and she was fine. So anyway- Thanks Delmar & Mobiltech. You convinced us to keep punching away at what we thought was good enough.