Jaguar Repair: Engine misfiring, 1986 jaguar xj6, jaguar xj6

Question
Hello,
i own a 1986 jaguar xj6 and i can usually find the problem but i am stumped right now. when i crank my car i have three cylinders that misfire the car has close to 150,000 miles on it. i checked out the ignition system but the coil pack and the distributor all work fine. when i unplugged the fuel injectors for the three cylinders the rpms dont change. usually i would just go with bad fuel injectors but this occurred all at once with no warning. also one of the cylinders that misfiring already has a new fuel injector in it. so i wanted to check with you if you have any idea of what the problem can be. im starting to look at either the timing chain, or the ecu.
thanks,
mike.

Answer
If your ignition system is okay, then you are saying that you are
getting a spark to your spark plugs. If your spark plugs are good,
then all you need is fuel in the cylinder. Check to see if fuel is
coming out of the injector by removing one. Your engine cylinder
should fire if you are getting fuel, a spark and air to your cylinder.
Remove one of your spark plugs and make sure the cylinder is not flooded
and that you are getting a spark. You might want to remove each one of the
affected cylinder spark plugs and see if fuel is being blown out of each
cylinder. If no fuel is being blown out then you are not getting fuel to your
cylinder. I hope that this helps. Sam