Question: Autopilot behaving badly
I am a new owner of a 1988 Pacific Seacraft 31. It has a Raytheon ST4000 Plus Autopilot which works great when sailing with the engine off--holds a steady course in most conditions--but whenever I have the engine on, whether motoring or motor-sailing, fast or slow, the boat oscillates wildly from side to side and I have to shut the autohelm off. I am assuming the engine is interfering with the autopilot's compass. There is a decal on the forward bulkhead indicating the compass is located somewhere there, and of course,the engine is aft, so they are far apart. I consulted the owner's manual but there is no mention of this in the troubleshooting section. Any suggestions on how I should proceed in fixing this?