Hello folks,

I have a 1987 XJ-6, and it runs very rough when cold. Car must get to operating temperature before more than 1/4 throttle is applied or it loads up, misses, and smokes (black) Plugs get black almost immediately. Once at op. temp, car runs okay, but idle is still lumpy. Any ideas on where to start?

Thanks

Jim - Kansas City

 

I have exactly the same problem with a 1982 XJ6.

There are half a dozen possible solutions. It could be a malfunctioning Thermotime switch, which activates the cold start injector. Try disconnecting it and see if that solves the problem. My system is to try disconnecting things, one at a time, and see if that isolates the problem -- water temperature sensor near the rear of the intake manifold, oxygen sensor on exhaust manifold, etc. I haven't solved mine yet, but I think it is the airflow meter malfunctioning. The car idles fine with the meter disconnected. Unfortunately, I can't run the car with the airflow meter disconnected, because the ECU doesn't recognize that there's a lot more air going into the cylinders when I drive it, and the poor thing leans out and dies. And new airflow meters are damned expensive.

Jim T

 

Thanks Jim - its a place to start - where is this thermotime switch located?

 

I don't know if you have the same engine I have. Mine is the old (continually improved since 1950 or so) 4.2 litre six. If you have the newer 4.0 AJ40 engine, I can't help you.

On mine, the Thermotime Switch is at the front end of the intake manifold, on top, just ahead of the coil. It should have a brown snap-off connector going to it. The water temperature sensor is near the back end of the intake manifold, roughly above the throttle cable. The cold start injector is about half way along, and lower down -- if yours is like mine, it will have a blue connector.

I can almost (almost!) guarantee that the problem will be a malfunctioning sensor of some kind, since the problem seems to be temperature related. But which sensor is another question. If in doubt, I don't think you can do any damage by disconnecting the various sensors one at a time. The worst that can happen is that the engine will quit, and you'll have to plug things back in and restart.

If you do figure it out, please let me know, in case it's something I've overlooked. As I said, I think mine is the airflow meter, but I really won't know until I get a replacement and see if that cures it.

Good luck

Jim

 

cool - thanks Jim. Mine is an old series III, not a XJ40, so the information you provided will be most helpful. I'll let you know what happens as I troubleshoot.