have a 03 4.2 just had intake gaskets replaced new fuel, air filters and just developed a miss u can feel in the pedal if u keep the rpms up it runs semi ok but taking off or if u shift to early it realy heistates or misses bad i replaced the plugs with autolite platnums the yesterday and as soon as i was done problem was fixed ran great all day no problems .. after starting this morning it if wors than it has ever been i am clueless as what to do being it ran great for a day with new plugs .. now what any help would be great thanks

 

How old are the plug wires

 

i dont know i bought the truck from dealer 2 months ago plugs looked old but would tthe wires do that ... idol fine and just miss the way it does...i just got back in from the store and it ran fine i dont know why it is hit and miss like this

 

Start it at night... And see if you can see any of the plug wires arcing.... Or jumping fire..

Is the check engine light on.. Or flashing?

 

Not too familiar with the V6's but I'll take a stab at it. Fuel injector? It's weird that it idles ok and runs in the higher rpms ok but it's missing at lower rpms when under load. Sounds like it could be running rich or lean. Are you getting the check engine light? Have it scanned and tell us what codes (if any) are you getting.

 

ok no engine light has came on or flashed though out this whole missing episode. had it scanned today to see if their were any stored codes and their were not.. the only thing that gets me is that it has ran fine all day so far it just missed really bad this morning on the way home.. thats why i couldnt see it being an injector how it is running fine or is that possible and with the plug wires when it does goes into these missing episodes.. it seems to run better if u keep te rpms up rather than if u were driving normally and just gave it alot of gas is when it is the worst.. but like i said it had been doing bad the oter day.. changed plugs problem fixed the whole day.. parked it the next day while i was at work(24 hrs) and this morning on the way home it was missing horribly.. and so far the rest of the day it has ran fine .. i just dont understand lol

 

Change the plug wires, if it needed plugs it probably needed wires as well...

A small split in the jacket of a wire could make it arch when cold, then when she warms up the jacket can swell and expand and close the hair line split...

Could be just an intermittent arch...

 

Did you wash the engine? Dumb question but if you get those plugs wet it's gunna run like junk until you blow out the water in the spark plug tubes also if you replaced the filters make sure you check all vacuum lines one may not be secure on the nipple or has a crack in it so at higher Rpm with the engine torque it shifts just enough for it to cause a leak and run like junk but not big enough to throw an engine light another thing to check is the fuel
Filter if you have recently fueled up at a Bo Bo gas station could be bad fuel lemme know what happens

 

My truck is doing the very same thing- I have the 4.6 V8.

I recently put in some concentrated gum out- and the problem has *slightly* improved (it hasn't gone away but it's still there). Some folk I talked to think it could be an O2 sensor or EGR problem.

 

Check the coil pack for signs of cracking in the housing. Sometimes will have cracks in the bottom of the coil pack. Known problem with the new style 6-pack coils! Spray just the coil with water. Can also use a test light, alligator to ground and poke around the coil. See if any stray spark jumps to the end of the test light.