had a check engine light that said #3 cyl. misfire. put on new plugs, wires. now the truck skips and shakes under loads(hills) or acceleration. looked under hood in dark and have sparks around plugs whan motor is revved up. is this a bad coil pack? i have no check engine light anymore.

 

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what year truck and what motor? if it is a cop coil orver plug there is no coil packs,
But it sounds like you have bad wires. Were they wires you put together if so you may have screwed them up, take them back apart and crimp them or fit them better, if they were wire that came premade then take them back. I would say plugs but the spark would go straight to the block.

Lance

 

thanks for the reply. its a 99fi50 with the 4.2l v6. i bought the wires from autozone, but they were a top end set, and i used motorcraft plugs of course, they were $4 each. i also thought i may have got a bad set of wires so i got another set, put them on, same thing. i originally did the tune up saturday, drove to atlanta and back(about 80 miles), and the truck ran great. then monday afternoon these problems started. since, ive replaced the fuel filter and cleaned the injectors. not getting any better.so i dont want to throw a coil pack at it for no reason. i checked the primary resistance on the coil, and it was o.k. at .7 ohms, but the secondary resistance was high on all three coil pairings, from 14.78 to 15.02. the book says it should be 6 to 11.5. would these readings cause this? thanks alot

 

99 f150 4.2l v6efi.. needed tune up, had a #3 cyl. misfire code. put on a good set of plugs, wires. ran great for two days, then developed a major shake and skip whenever accelerating hard or going up a long hill. thought i might have got bad wires so i replaced them and that didnt fix it. neither did cleaning the injectors and replacing the fuel filter. i now think its the coil. primary resistance is ok, but secondary resistance is high. mine read from 14.78 to 15.02 and the book says they should be from 6 to 11.5. any body else ever had this? am i probably right about the coil? i dont have the check engine light anymore.

 

I would check to make sure you have the right wire on the right plug, crossing the wires is easy to do. As far as AutoZone wires, Avoid them if you can, thats from my expearence and opinion. They are for use in a pinch. Make sure the plug wire is pluged on the plug good. Ohm the wires out to check the set. Bad rubber boots on the plug end may be letting the spark jump to the wall of the plug hole. Good luck.

 

I agree with Bosshoss, check for crossed wires just to be on the safe side. so you tried two sets of plug wires, before buying another set or taking thoses back do you still have the old wires? If so on the plug that the spark is jumping put a old one back on and see if the spark jumps. If not them you know its the plug wires. If it still jumps then The plugs need to be looked out as a posssible problem although doubt ful. It does happen,

Lance