Will a 1988 jaguar xj6 stall if a catalytic converter is stopped up.

Any codes?could be a misfire and could plug catalytic converter.

That much time running sounds like the catalytic converter is plugging off and stalling the engine.

where is fuel relay located on 1988 jaguar xj6

TO RESET ECM ON A 1988 XJ6 JAGUAR.YOU DISCONNECT NEGATIVE BATTERY CABLE FOR 30 SECONDS TO CLEAR CODE.THIS WONT DO ANY GOOD IF YOU HAVE A ECM TROUBLE CODE DONT FIX PROBLEM.CHECK ENGINE LIGHT WILL STAY ON, UNTIL YOU FIX FAULTY COMPONENT OR SENSOR.

I have the similar problem with both my Jaguars, one is a 1988 Jaguar XJS, the other is a 1987 Jaguar XJ6, both blow COLD air out some vents while it blows warm air for heat. I heard it had something to do with the cold air blowing as a dehumidifier, I don't know if this is true, but it is really annoying to have both cold and warm air blowing when I need heat in these cold Canadian winters. If you find out please drop this website a note and let us know how you solved it. thanks.

Ok Andy, This sounds like a ddefective #2 02 sensor located afther the catallytic converter. This sensor is the critter that turns the light on and that means it is talking to the electronic control module. Either your fuel misture is way too rich or the cat converter is failing. Good Luck-Ned-

The code P0420 is the catalytic converter, you need to get this checked, by an exhaust specialist or mechanic with the correct equipment/ testers ,if the cat gets badly blocked it can stifle the engine and gets VERY hot , so being a danger of fire. I have seen these glowing bright red.
Hope this helps

master cylinder needs to be rebuilt or replaced

Fuel pump is bad or plugged fuel filter it seems. Crack the line from the filter leading towards the engine first. If gas starts squirting out fast, you have good pressue. If not the filter is plugged or a bad pump. How old is the fuel filter by chance? If original its plugged up by now

your heater is just set on automatic, it will turn off and on to keep the the air at the same temp. Its basicaly like an early climate controll. there is a button that says manual that should stop it from doing it on it own. the button is towards the left by your heater settings. I have the same car and that baffled me for a while!