My 2000 honda coupe vtech 4 cylinder missfires throughout driving range. Have changed plugs, wires, distributor cap and button, coil, engnition module,and egr valve. The computer has no problem codes. Do you have any suggestions? The motor has 150k on it.

F it is missing randomly, or intermittently, its now time to check the fuel pump, and filter(s) out. On older vehicles, there is usually a easy to locate fuel pump under the hood. Mounted on the side, or front of the engine block. If it is located on the front, chances are, its sits close to the bottom of the motor.

Lets start with the idea that it only misses when you have your foot in it. Does it miss badly when you have your foot in it, or only intermittently? Does it feel/sound like it is missing at a steady pace, or randomly? If it is missing all the time you have your foot in it, and is steady, that means that chances are only 1 cylinder is having a problem. Which makes thing easier yet. Assuming that there is only 1 cylinder with a problem, if your vehicle has fuel injectors, grab the ye ol' trusty ohm meter, and set it up to test resistance/continuity. Take the wires off of one of the fuel injectors. Put the 2 prongs from the ohm tester on each prong of the injector. You should get a reading. Now, put those wiers back on just as you had them before, and take the wires off of another injector. Test it with the ohm meter. All of the injectors should have a similar reading. If there is one that is way off of the others, that means that injector you are testing is most likely bad.

Although the possibility of a mis adjusted air/fuel ratio is not negligable, chances are, that this is not causing the problem. If nothing above has solved the problem, your problem lies in these things including but not limited to: Brain Box (If applicable), various sensors (i.e.; O2 sensor, MAP sensor, cam sensor, crank sensor, etc.), and vacuum hoses/valves (i.e.; PCV Valve, EGR valve). Make sure that all of the vacuum hoses are connected properly and are not deteriorated and leaking. A good way to tell if a vacuum hose is leaking, is to listen for a hissing noise while the engine is running. On older cars with an air cleaner unit on top, there may be a mess of vacuum hoses underneath of the cleaner unit. Check to make sure that all vacuum hoses underneath are connected properly in the correct location. For most sensors, you cannot test them. Other than noted in a "Chilton" manual, testing of sensors is basically impossible. Other than to replace them, you will never know. Once again check over ALL electrical connectors, and wires, vacuum hoses, and that there are no leaks anywhere. Worse come to worse, you may have an internal problem, and problems such as those are noticable by means of a knocking noise, or other deep internal noise. Unless the motor is worn out, or abused, the chances of an internal problem are not likely.