van has a constant miss on 1999 Mercury Villager

one code reader said cylender 4 misfire, so i changed plugs. still missed. my mechanics reader said random misfire, he said change wires, i did. still misses. is there a coil pack? should i look there?

by in Pittsburgh, PA on December 17, 2010
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2 answers
ANSWER by , December 17, 2010
First you need to find out why #4 cylinder was missing, was it a plug, a wire etc? It could be a lean condition, so I would check your Long Term Fuel Trim, that can cause a random misfire, or a leaking intake manifold. Make sure that your Long Term Fuel Trim is not above 9% for either Bank 1 or Bank 2, if it is, you may have a vacuum leak or a defective Mass Air Flow Sensor or other things. I would also do a compression test just to be sure that the engine is still tight, you want to see at least 150 psi in all cylinders.
ANSWER by , March 19, 2012
Try the distributer cap and rotor. Could also be a bad injector (of somthing else in the fuel system) or something mechanical. Run a compression check on the cylinder.