Hello all and happy 2018! We just bought our third XJ6, but this time a series II. Our Excursion just lost third gear, so we needed an inexpensive car to drive while I fix the transmission. We found a nice '79 XJ6 for dirt cheap and jumped on it. Exterior is perfect with nice original paint. I'm curios if anyone knows the name of the factory paint color? Anyways, it starts up and drives nice, but after a few minutes it sputters out and dies. I then have to wait maybe 10 minutes for it to start again. Initially, I was told it was the catalytic converter being plugged up. It would glow red hot after a few minutes of running, and seemed to start after cooling down a bit. So in order to drive it the 55 miles home, we unbolted the cat and hoped thay fixed it... it did not. Any suggestions? I have a few thoughts of my own:
A- Vapor lock. But it was raining and cold, not hot outside at all.
B- Alternator or battery. Once it dies you get a couple good cranks before it needs a jump start or a charger on the battery.
C- Fuel filter or pump.
D- Coolant leak from thermostat housing directing above the distributor. (This one actually makes the most sense in my head. engine warms up and leaks coolant onto distributor and wires, causing it to not spark. Then once it's dried off a bit it starts back up.)

when I'm trying to start it, it sounds like only one cylinder is firing, then suddenly the rest chime in. Any suggestion?

 

In 1979 the only brown listed is Chestnut Brown Metallic. In 78 there was Carrage Brown which was not a metallic paint. In 1980 there was a dark brown called Grosvenor which I know well and must tell you is what your photos look like. Could the car have been carefully repainted?

 

I'll take stab...Is that one fuel injection or carb. I thinking FI in 1979 so first thing I would do is install a new fuel filter. The fuel tanks in these cars are notoriously problematic, they runt and can plug a fuel filter quickly and some times in the process they destroy the fuel pump too. Cut open the filter after you remove it to know for sure.