1994 XJ12 - misfire under load

Hi All,

Back after a long hiatus. I’ve got a 1994 XJ12 in storage which will start and move around under it’s own power. It will start quickly and idle OK, seems to be hitting on all cylinders (fast sometimes) and then when I drive it around the block it will work great for a few hundred yards, then start misfiring and will barely pull itself around. After it sits it will start up and idle again OK.

It’s been off the road for probably most of 5-10 years. I have an appointment in May to get it in to Champions Jaguar in Houston to get it road-worthy again. Should just go ahead and change plugs, wires, cap, rotor, coils, and fuel filters just as a matter of course before I take it in? I’m comfortable doing my own wrenching but not really into hard-core troubleshooting. I’m wanting to get the car to usable condition for a local weekend driver. This is my last Jag and I’m fine with spending 3-6K on it, and am willing to change more than I need to and not have to revisit similar problems over again.

Tim, welcome back.
I’d clean the mass airflow sensor first then check the plugs.

Anything you can do thats going to save the shop time will be in your favour, if you are comfortable doing the spark side of things thats one less job.

You might have the beginning of a Marelli ignition failure. I wouldn’t drive the car at all until the cause of the problem is identified.

I would go ahead and replace the parts you’ve mentioned, yes. When you remove the distributor cap the problem might become immediately apparent, in fact


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Thanks! I’ll put this on my list of TODO before I take it in.

Yeah, I kinda figured as I wrote it, depending on anything that’s easily changed and is more than 10 years old is probably a false economy… lol Time to schedule some quality time in the storage unit with my cat…

Thanks Doug, I think I’m going to do as much simple wear-and-tear stuff as possible before I take it in. Can’t hurt. The car isn’t getting driven at all right now, it’s tucked away in my storage unit for the time being. I’ll get over there and start working on it.