Twr00378 - Cat 930G stalling when lowering or dumping bucket. I can raise bucket no problem, I can tilt back the bucket and no problem but when I try to lower it or dump the bucket you can hear the engine trying to stall and if I keep trying to lower or dump it does eventually stall. I'm getting a high reading on the backpressure test point located on top of the valve main valve. Don't remember how much exactly right now but it's about 3000 psi. I've eliminated the lower / raise valve for now and just left the tilt valve connected but still stalls when trying to dump bucket. It has a 4 way single joystick. Any help would be appreciated.
High return/backpressure is the key clue. When you lower or dump, a large volume of oil must flow from the cylinder head ends back through the main control valve to the tank. If that return path is restricted, pressure builds in the return circuit (your ~3000 psi reading), which loads the pump and stalls the engine. Raise and tilt-back work fine because those functions demand less return flow or use different passages. Most Likely Causes 1. Restriction in the return circuit (most probable given the high backpressure reading) • Plugged or restricted hydraulic return filter / screen • Collapsed, kinked, or internally failed return hose from the main control valve to the tank • Blocked tank return port, internal tank screen, or baffle • Stuck or restricted back-pressure / check valve in the return path (if equipped) 2. Main control valve internal issue on the dump/lower return passages Since you isolated the lift section and the dump still stalls, the problem is either shared return or specific to the tilt (dump) section. 3. Less likely but possible: pilot-related or load-sense issue that only shows under high return flow conditions (there are documented 930G cases of dump-only stalling tied to pilot pressure or valve problems). Recommended Checks (in order) 1. Confirm the backpressure reading Re-measure the pressure at the backpressure test point on top of the main valve while actively dumping or lowering. Note the exact pressure and whether it spikes only during those functions. 2. Inspect the entire return path • Remove and inspect the hydraulic return filter/screen. Replace if dirty or restricted. • Trace the main return hose(s) from the control valve to the tank. Look for kinks, collapse, or external damage. Disconnect and check for free flow if possible. • Check the tank return fitting and any internal tank screens/baffles for blockage. 3. Main control valve • Since the tilt (dump) circuit alone causes the stall, inspect the tilt section return passages, makeup/check valves, and any associated reliefs or resolvers for debris or sticking. • Clean or swap components between lift and tilt sections if practical to isolate. 4. Pilot and load-sense (secondary) • Verify pilot pressure is within spec under the conditions that cause the stall. • Check that the pump is destroking properly (margin/load-sense pressure) when functions are held. The combination of function-specific stalling (lower/dump only) + high measured backpressure almost always traces to a return-side restriction. Start with the return filter, hoses, and tank inlet — those are the highest-probability, lowest-cost items. If those are clean and free-flowing, the main control valve return passages become the next focus. If you can provide the exact serial number (TFW or TWR prefix) and the precise backpressure reading while dumping, more specific port/test locations can be referenced.
Thank you so much for responding and for taking the time to write all that out. You have no idea how much I appreciate it. I took a week off from working on it to rest my brain a bit but I will definitely start back up on it this weekend. Again much appreciated. I will get reply back once I start working on it again..