My 06 F150 will misfire when the engine is under a slight load. I suspect one of the coils or a plug is going bad. I took it to two different auto parts stores to get it scanned and both said that unless the check engine light is staying on (it's not) they would not be able to tell me which cylinder is missing. How can I determine which one is missing?

 

You need a better scanner than what the auto parts store is running

 

Do you have a model number ?

 

is pretty nice. I prefer the bluetooth ones as you can do a lot more with them than just a basic scanner.

 

Ok, so exactly what specification should I be looking for in a scanner that will tell me what cylinder is missing even though the check engine light is not on?

 

Read my post here. You prob should replace all the plugs and any boots that have carbon tracks.

 

That is a link to the entire website , do you have a brand and model # ?