I have a 1995a XJS 6 cyl and with new coil packs, the engine still shows spark plug fault on #5 and 6. Is it possible that the wiring harness to those 2 plugs is at fault or can the ECU give the same result? Engine runs buts misses because of the fault. Can ECU be checked and what kind of service would do that ? Nashut55

 

Welcome to the forums 1955ambassador+,

I've moved your question from General Tech Help to XJS forum. Members here with the same model will be able to help.

Please read the guidance for new members ( https://www.jaguarforums.com/forum/n...ned-up-241802/ ) which answers many of the most frequent questions about getting started.

Graham

 

Welcome to the Forums.

YES.

The X300, same engine, has issues with that harness where it bends at the rear of the engine, which is aggravated when bent further when changing spark plus or coils.

One wire at a time, rebuild the harness.

 

As long as you are sure that you didn't use the plug for #6 on the #5 coil and vice versa, sounds like the wire is the suspect here. (I'm not sure that's easily possible with #5 and #6, #1 and #2 on the other hand....)

You are getting codes p0305 and p0306?

Only other thing to easily check for is corrosion on the pins of the ECU.