[v12-engine] Re: Cylinder Testing

There is a miss in my '86 XJ-SC V12. What is the best way to shut
down the cyinders on at a time so that I can identify the cylinder
that is missing?

Use a long-nosed, insulated “spark plug wire puller” type pliers. Remove
each of the spark plug wires, one at a time (this can be done at the top of
the distributor cap, or at the spark plugs). If the engine did not show a
change of any rpms (listen, or look at the tach), then that particular
cylinder is not getting fired. If there was just a slight change, then
that cylinder may be creating a “miss”. If there was a significant change
(should be close to the same change as the other cylinders), then that
cylinder is performing correctly. You may notice a spark trying to jump
from the end of the spark plug wire, to the closest ground point (in
respect to where you are holding the end of the wire). If the spark is
jumping, but no change in the engine, then sheck the condition of the spark
plug. Replace the spark plug wire, and do another cylinder. You may want
to observe the engine bay at night (engine running, hood open, lights on
the car, and your garage area, turned off), before pulling any wires, to
see if you notice any stray spark arcing occurring, such as from the side
of a spark plug wire over to a ground point. If all the wires and splugs
test as “good working condition”, then you will have to check the
injectors, to see if one may be faulty (electrically or mechanically).

Tex Terry, II
86 XJ-S Coupe V12 GM400 DANA 2.88
Franklin, PA USA

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