If your log splitter is bogging down under pressure, there are a few potential causes. First, the piston could be dirty or damaged. If the piston is dirty, it can't move as freely through the cylinder, which will cause the engine to work harder and eventually bog down. If the piston is damaged, it may not be able to create enough pressure to split the logs. Second, the hydraulic fluid could be low. This will cause the pump to work harder and eventually overheat and bog down. Finally, there could be an issue with the valves. If they are sticking or not opening properly, they won't allow enough fluid to flow through, causing the engine to bog down.
To troubleshoot this issue, start by checking the piston. Clean it if it's dirty and replace it if it's damaged. Then check the hydraulic fluid level and add more if needed. Finally, check the valves for any sticking or blockages. Once you've addressed all of these potential issues, your log splitter should function properly again without bogging down under pressure.