I am a first time Jag owner. My 1989 XJS V12 convertible currently loses power when put in gear. the rpms go from 1000 to 500. Cant make it up a hill. no acceleration. in park or N the RPMs are steady and revs appropriatley. It has a dual cooling fan and the drivers side fan will not engage. I began experiencing these symptoms after loosing the drivers side exhaust. It drove fine ( actually better ) for a day after removing the exhaust that was hanging down from the converter. Its the Lucas system. Any insight into this would be greatly appreciated.
Offhand, sounds like the exhaust system may be obstructed. Remove an oxygen sensor and try driving it. If it runs better, that confirms the exhaust system on that side is obstructed.
Could be the plugs ,my boat did that to me would idle fine but when put in gear no power changed the plugs ran fine .
So the exhaust is now fixed or disconnected? If so where is it disconnected or loosened? If it is at the manifold, wouldn’t the ECU artificially enrich, potentially to where that bank’s plugs foul and loses power? And wouldn’t disconnecting the battery reset this to test it?