Good morning!
Just got into my third XJ this last weekend and have come across some issues. It is a 1998 XJ8 with 115K miles. I got a good price – however, I knew there would be some work to get up to speed. First off my diagnostic tool gave me some error codes (misfiring) in particular with cylinder 4. I replaced the spark plugs and noticed a couple were pretty fouled. I switched the coil from 4 to 1 just to make sure that was the problem… sure enough. Now cylinder 1 had the misfire and I’ve ordered a new coil pack.

The thing that’s got me a little concerned is a knocking that comes and goes. I’m trying not to get too worried before I replace the coil. When I start the car it lopes a little and there’s a knocking from (maybe the rear of) the engine. When I accelerate - it goes away (sometimes the cylinder misses some time runs fine) but gradually when the car settles back to idle the knocking returns. It did need to be topped off with oil but it certainly was not dry when I got it. Of course I plan on changing the oil when I replace the coil when it comes in. I suspect the car had not been driven much over the last year or so.

Anything I should also be checking?