Volvo: 960 rough running, oil ring, electronic module

Question
Is there a way that I can tell which cylinder is not firing. Would it be to disconnect the coils, one cyl at a time, and see when the engine is not affected?  And would that be a bigger possibility than an injector not working?
Thanks again,
Gerry
-------------------------

Followup To

Question -
Hi, thanks for being available on this site.  I have a '94 960 with a '93 motor that is running rough, like one cyl is not firing most of the time.  A warm compression test showed all cylinders hitting about 185-190 psi except # 2 that was about 175.  I replaced all of the plugs with new ones.  Could the problem be a electronic module for the plugs or an injector?  And is there a way to test these components?  I can take this to the dealer for testing if necessary, but would like to have an idea of what it could be.
Thanks again

Answer -
Gerry,
The low compression cylinder is really not "too low" and possible being caused by all the fuel in that cylinder washing out the oil in the oil ring, because of the no firing in that cylinder. Yes the coils could be bad. You can move a coil to another cylinder and see if that one will not fire therefore verifying the coil is bad. There is an ohm reading of 0.5 on each coil.

Answer
Gerry,
Unplugging the coils will possibly indicate the cylinder that is missing, but then you need to see if it is missing because of spark or fuel. Pull the suspected coil and install a plug and crank the engine briefly to see if there is spark. That should tell you if there is spark or not.