Have a 1985 sumitomo s160 f2 excavator about 7.5 tons. Has a 4jb1 Isuzu motor. It's started spuddering a lot and trying to stall out. I cleaned the fuel tank, replaced the fuel line from the tank and have replaced the fuel filter numerous times. Seems like it gets worse when I get the machine rocking and bouncing alittle bit. When I stop and let it idle it will clear up but when I get working again it starts acting up. I assume a bad injector wouldn't go in and out of running good and bad but I'm not a mechanic. Any help would be appreciated. Thanks
What kind of junk came out of the fuel tank? The first thing I'd suspect is that you still have a blockage between the tank and the injection pump. I have no idea how that injection pump fails, and that's the worst possibility, so eliminate the simple stuff first. If this has a manual transfer/priming pump that you unscrew the piston and pump up and down, then there's usually a screen in the banjo bolt on the intake underneath that pump. Check that, and once you've opened the system take it apart back to the tank and blow it out. The transfer pump could be weak, anything could have happened over 30 years. You can also tee into the inlet side of the filter and see if the pressure holds steady or drops when it's stalling.