You should have the Motorola ignition. If you get spark on any one cylinder, the unit is good and you should get spark on all cylinders. Thus your coil and high tension lead are good. The problem would most likely be with the #4 plug or associated wire.There should be very little resistance in any of the plug wires. This engine uses solid core stranded wire. SO: Check the plug itself, check the plug terminal. Finally, remove the distributor cap. Check the contacts inside. Look for carbon tracking which would short out the #4 terminal inside the boot. The plug terminals are spring steel clips that simply stab into the wire. They frequently rust and break.. Split the cap and remove the top (two round head screws, one on either side of the high tension lead.). Then pull out the rubber seal. see if the #4 wire is seated fully on the recessed prong