I have a 1998 ford f150 truck and the engine misses,I changed the spark plugs and spark plug wires and it still misses,what could the problem be?

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Test and Procedures:
1. If a Ford factory scan tool is available, use the power balance test to isolate the cylinder. If a factory scan tool is not available, use of mode 6 data may help isolate which cylinder is misfiring. Misfire will be under 51 or 53 modes depending on year of vehicle.

2. Once the correct cylinder is isolated, move that cylinder's coil and plug to another cylinder, if the misfire follows, replace that coil and plug.

3. If the misfire does not follow the coil and plug, move that cylinders injector to another cylinder, if the misfire follows, replace that injector.

4. If the coil and injector are ok, test the power to affected coil and injector during misfire, if ok, check the ground side pulse width during the misfire and compare to a known good cylinder. If the pulse width to the coil or injector is lower on the bad cylinder, suspect a circuit fault between the powertrain control module and that cylinder.

5. Note, generally the powers to the injectors and coils will all be the same color, however the ground side will be different color on each.

6. If all coils, plugs, injectors, circuitry are proven ok, suspect internal engine fault, begin compression and running compression tests to isolate.

Potential Causes:

Coil on plug
Spark plug
Injector
Powertrain control module
Circuitry
Internal engine
Also try replacing fuel injectors. Good luck.