What is the function of the temperature sensor/switch located at the very rear position on a 1986 XJ6 Series III XK engine? (Not the coolant temperature sensor which is forward of that.) I’m experiencing rich fueling and very rough running on a cold engine until thoroughly warmed up and just want to be certain that sensor/switch is not causing the problem.
The engine runs very rough and has no power until thoroughly warmed up and then runs perfectly fine. Running the cold engine at around 2000 RPM allows it to run well enough to stay running until warmed up but even then it still runs very rough and rich. I’ve replaced the CTS, fuel pressure regulator, O2 sensor, ignition amplifier module, and ignition coil. Engine grounds have been cleaned and connections soldered if no already soldered and vacuum hoses replaced. The Auxiliary Air Valve has also been verified to be working properly but not replaced. The AFM seems to be working just fine and can be adjusted to reduce the over fueling problem when cold but then must be readjusted when the engine is warm to allow the engine to idle smoothly.
At this point it seems to me that nothing is left but the ECU to be causing this problem, but I hear from some others that the ECU doesn’t usually cause problems. I recall reading somewhere that the capacitors located within the ECU circuit which controls fueling of a cold engine may drift out of performance spec with age and therefore could result in an over fueling problem with a cold engine.
Any ideas about what to do to solve this problem would be greatly appreciated.
That is the Thermal Switch (EAC3762) that is part of the Air Injection System that includes the Air Pump, Air Injection Switching Valve, Air Rail and other components that inject air into the exhaust gases downstream from the exhaust valves when the engine is cold to aid in combustion of residual unburnt fuel. I can’t see how this switch could be directly related to your rich fueling and rough running problem.
The Jaguar XK engine was installed in a lot of Jaguar models from the late 1940s until the late 1980s. This is not a XK engine problem but a problem with the XK engine as used in the fuel injected Series II and III XJ6s. I recommend that you post your questions to the XJ list and you will probably get some more help there. I recall others on the XJ list writing about a capacitor mod to the AFM that has solved this kind of over-fueling problem. I haven’t had that problem myself with my two XJ6s so I can’t talk to this first hand. If you check the archives you might find more information about this. Perhaps others might chime in as well.
Thanks very much Paul for the reply. I’ll try posting in the XJ forum but did so about three months ago and did not receive any replies which solved the problem. Was hoping the engine forum might turn up some folks who could help identify which capacitors in the ECU I should be testing and/or replacing.
