Toyota Repair: failing emissions test, emissions test, toyota pickup

Question
We have a 1994 Toyota pickup with a 4 cylinder/standard transmission. It can not pass the emissions test. To much unburned fuel in the exhaust. We have replaced the spark plugs,the distributor cap and rotor. We have replaced the distributor wiring harness and the tail pipe oxegen sensor.When replacing the spark plugs the back cylinders plug was fouled. After replacing it and driving it for a while we pulled the back plug was not firing as well as the others. I suspect a fuel problem at cylinder #4. Whats do you think.

Answer
I think that there may be a compression loss in the #4 cylinder that is causing a misfire, high HC readings are aways caused by inclomplete combustion which means there is cylinder inefficiency which translates into a misfire condition that could be caused by a leaking valve, the first thing I would recommend is to have the engine compression tested and I think you will have your answer.