Hyundai Repair: Hyundai Excel Misfire, fuel management system, hyundai excel

Question
My wife has a 98 Excel twin cam that boiled over on the weekend due to the 20Amp cooling fan fuse having blown. I replaced the fuse and the fans and replaced the water in the radiator about 2.5 lites required + the overflow tank. The car starts OK but misfires and lacks power. I checked the compressions and got 200, 190, 200 and 200psi. I also replaced the spark plugs which were in for 3 years. The car starts easily and blows no smoke. The water in the radiator is as clean as a mountain stream with no oily film and oil in dipstick is like wise. Any ideas? Thankyou

Answer
You should make an extra-close inspection of the plug wires.  It's possible that the heat has damaged them.  Ultimately, you'll probably need to isolate which cylinder is misfiring and then try to find the specific cause of the misfire.  

I'm not sure what fuel management system or engine you have.  Presuming the injector connectors are easy to get to (and that you have fuel injection), disconnect each injector one at a time.  If you unplug an injector and the engine doesn't run any worse, then that's the misfiring cylinder.  

Once you've located the misfiring cylinder, remove that wire from the spark plug and install one of the old plugs in the end of the wire.  Then lay the plug on a metal grounding surface (away from the fuel system).  Restart the car and observe the plug.  If it doesn't spark, you've got an ignition issue and you'll need to check the wire and coil.  If it fires, you know that you have spark and should move on to checking the injector.  

To check the injector, unbolt the fuel rail and swap the injector in question with another.  Then restart the car and see if the misfire moved along with the injector.  If it did, the injector is your issue.  If not, then it's elsewhere.