NEED Help with Caterpillar 963B fuel issue

I am looking for some advice in regards to my 963B. The machine runs great when I have got it running. I am battling, what I believe, is a fight to keep the fuel line primed / pressure in the line. Here is what I can tell you and what I have tried:

Machine will be running/operating and dies by itself

I will then spin off fuel filter and check... it is full

If I break one fuel injector loose and use the hand pump to pump fuel to the injector (like re-bleeding the fuel line), the machine will then start and run

Once I do this process, it will run for about 4-6 hours before I have the same issue.


If I use the machine and park it operating correctly and arrive the next morning to use it, it will start right up.

If I park the machine for 3+ days, it will not start, when I spin th fuel filter off it is still full.

I then have to re-prime to get fuel up to the injectors.


Does anyone have an opinion or experience with this issue? Does it sound like the fuel filter hand pump, or does this sound like an injector pump problem?
Thanks in advance

hello, when you say you crack a fuel line loose to bleed what line are you loosening. according to cat sis the 963B loaders have a 3116 engine in them which have no external fuel lines to the injector. is your engine the 3116 ?

Uisng the hand pump will not pump fuel as far the injectors. It is a very low presure priming pump that will only pump fuel as far the rack gallery in the main high pressure fuel pump. That's the long thing with the pipes running from it to the injectors in the cylinder head in a noraml diesel engine. (the 963 has internal fuel lines apparently, but I don't know the 963 engine that well). After that point, the high pressure "piston pumps" create the very high pressure required to "pop" the fuel injector.

Other than that I suspect you have an air leak on the suction side of the lift pump (aka the transfer pump) wich draws fuel from the tank and pumps it into the fuel gallery as above. Pulling fuel filter will tell you little or nothing as it will always be full long after the air in the injectoion system has caused the engine to stop.

I'd be checking all the union and fittings along the line from the tank to the transfer pump, check the rubber seals in the hand priming pump or bypass ir completely with a temporary line. Try putting an air line into the fuel tank and slightly pressurising the tank. You'll need a reasonable seal around the tank neck opening. If there's a substantial leak you may be able to see it as fuel coming out of the point of leakage. Run/syphon the fuel from a jerry can that is located higher then than the engine, into the filter line and see if the problem is still there. Air leaks on the suction side of any diesel transfer pump can be a real PIA to find and quite often one has to simply replace the whole line and fittings.

Another possible is a floater in the tank that can block the line to the pump, but this is rare. I've also seen a cracked suction pipe INSIDE that tank!! It took us a few days to find that one!

Ausse Les

I'm with Aussie Gold . We had a similar problem but on a Detroit , we run a new line and that fixed it

I have ordered a new hand pump to eliminate any doubt of an air leak on the original one on the machine. I have slight inkling it may be an air leak so I will swap that out and keep checking the simple possibilites and work my way into it.

A new pump is about 350 bucks. Why not just prime the system to get rid of the air then seal the pump with silicone all over and see if the problem disappears. There's only two points of entry for the air i.e - two pipe flare nuts and a the pump stem itself to seal with the silicone. You can buy a new rubber "O" ring for the pump which is a lot cheaper than a whole new pump and there's not much more in there that can cause an air leak. Don't spend the money until you're sure it's it's the hand pump that's causing the problem.

JOAT, a bit confused on what you have and others say you have for an engine. From what you say it sounds like a 3304 with a new scroll fuel system. The new scroll system has a fuel return line to constantly bleed any air that might get picked up back to the tank. It's the small line(1/4") at the upper rear of the injector pump. If it's clogged you may have to bleed your system often. Make sure it is clear back to the tank.
Later Bob

Hi Bob,
My sometimes right source says the engine should be a 3116.

That may be true Pete, but it all hinges on the machine actually being a 963B not just having 963B decals.
It wouldn't be the first time. I just get a feeling from his posts it's got a 3304 in it.
Later Bob

get this fixed yet ? Don't over look the obvious , had the same problem and it turned out to be the vent in fuel cap plugged . After running for awhile with no vent there is enough suction in tank that primer pump cannot draw fuel. The filters stay full because it isnt sucking air,it still is trying to draw fuel from bottom but just cannot overcome suction

I believe I have fixed the issue. The machine is not my everyday driver, so the little use I have done with it, all seems well. I had to change out the hand primer pump. This appeared to have a broken seal and internal part, it would not lock and hold, causing a large air bleed. So far it has ran fine.