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Notice inconsistent miss last week.  Problem has increased in frequency and is now consistent.  Servie engine light came on this afternoon when missing became constant.  Is this plugs/wire or something else?  How do I diagnose?  

get a scan tool..... see what codes are coming up..?????

it could be ignition , fuel injection or mechanical...

post a code...

if you examine the sides of the ignition coil... they tend to have external leaks and leave white dust rings on the round center near the square coil frame...

i would also swap on a new cap and rotor... if your truck is equipped... i take it that you have a TBI or a vortec..


the TBI and Vortec motors also have terrible problems with the intake manifold gaskets..  check yours for coolant leaks near the corners of the intake... they are plastic gaskets... so you cannot retorque them...  they have to be replaced...  the new gaskets are  wider around the water ports...   if your intake is corroded...   you can use high temp epoxy to repair any corrosion...

there have also been vortec injectors clog... and the upper intake manifold seals leak air..

there have also been vacuum hoses fall off..

start with the codes...     open the hood in the dark.. start it up.. look for arcing from the coil...  spray around the intake with some carb cleaner with the engine running.. looking for changes in idle speed..  thats how you find vacuum leaks..

then look for coolant leaks.. like i said.. it happens on almost every motor...