1989 F-150 4.9L smog fail

[quote:63b437e750="howard"]1989 F-150 4.9L 350,000 miles

New wires, plugs, rotor, cap, filters, oxygen sensor, throddle position sensor.
1st fail the CO% too high, I installed a oxygen sensor.
2nd time fail, CO% passed but the HC is too high;
Max. 118 Measure 205.
How can I lower the HC ?

Tom[/quote:63b437e750]

Excessive HC reading

Hydrocarbon failures mean unburned gasoline is passing through the engine and entering the exhaust. The three most common causes include ignition misfire, lean misfire and low compression (typically a burned exhaust valve). Ignition misfire can be caused by worn or fouled spark plugs, bad plug wires or a weak coil. Lean misfire results where there is too much air and not enough fuel, so check for vacuum leaks, dirty injectors or a fuel delivery problem. In addition to these, hydrocarbon failures can also be caused by oil burning due to worn valve guides, valve guide seals and/or rings

HTH-Good Luck