Hi all, I am interested in purchasing a John deere 992 excavator. It is a 1992 and shows 11,800 hrs on the meter... I know where the machine started from and has been maintained pretty good. Problem.. She only runs at half idle and the guy says it is a sensor issue.. Next problem.. Whenever you touch a joystick to move the arm or bucket, the machine smokes like crazy... At idle it runs fine and no smoke.. Doesn't matter if you are going int a pile or just rotating the machine, the second you put any hydraulic to use, she smokes thick black smoke... Any thoughts?
Try checking the intake manifold gaskets at the head. Look at them close. Use a mirror and look under the manifold at the head. Those gaskets get blown out and the engine will smoke black and fall on it's face when a load is put on. It was a common problem on those engines. The engine control problem could be anything. I believe the D model had a self diagnostic controller behind the seat. The engine speed sensor was a Hall Effect sensor. It was mounted on the flywheel housing and counted the teeth on the flywheel ring gear. It would get metal debris on it from the starter (the senor is magnetic). Sometimes you could remove the sensor and clean it. To reinstall the sensor, hand screw the sensor down until it hits the flywheel and back out 3/4 of a turn.