I have a 1991 Ford Ranger 2wd with a 3.0L vulcan, I changed the plugs and wires which I'd guess were original 160k miles on truck. Fired up the truck and it knocked. Ran fine before. Could there be a possibility that with the new plugs and wires the cap and rotor need to be replaced cause they arent putting out the proper voltage? Engine seems to be running rich. When I give it gas and hold it between 1500 and 2000 rpm knock goes away then returns at idle. Can anyone offer help!?

 

Well, first I would have also replaced the cap and rotor as they accummulate electrolysis corrosion on the tip of the rotor and the internal cap posts that inhibit spark transfer to the wires. Did you double check that the cap-to-plug wires are in the correct position? It's also possible to have a bad plug. You can either pul the wires one at a time to see which one causes the problem to remain the same, or start the cold engine for about 15 seconds, shut it down and feel the exhaust manifolds to see which cylinder is COLD.