I have a 2007 lariat 4x4 with the 5.7. I changed the spark plugs about 7 months ago because the dealer said the #3 cylindar was misfiring. Since then I have not had any problems until about 3 days ago. Now it runs like its missing again. About 5 days ago it ran rough after a bad rain storm and popped a #7 cylinder but after it warmed up, no issues. Now it is running like it has a dead cylinder all the time but no codes are popping. Is there any way that I can check to see if it's a coil pack without changing them or moving them from one cylinder to another one? Is there anything else that I could look at? Any help would be greatly appreciated. Thank you.

 

A coil is pretty hard to bench test, you can check things like resistance but that won't identify every problem they could have. For example if the housing is cracked and causing an intermittent short a multi-meter won't be able to detect that. Swapping the CoP only is a lot less work than the plugs, you should be able to do it without removing anything else and its the only way to know for sure. Intermittent electrial problems are the worst.

 

That's what I was afraid of. I would have no problem doings that if it was throwing a code but when it won't throw a code, it is like shotgunning parts and hoping it will fix the problem. Thanks for the help.

 

My bet is on #7 since it was missing before, but yea, it can be a crapshoot without a specific code.

 

It can be the coil, or it could be plugs or even a dirty throttle body. What brand of plugs did you use?

 

If you can find someone with a Real Scan Tool (Not a cheap code reader) Access OBD II Mode 6 (Perimeter 53) it will show misfire counts for each cylinder,A code does not have to be set to see misfire counts in OBD II Mode 6

 

There's a few ways to approach this, but you're going to be replacing a coil in the end no matter what.

Check all coils with a multimeter for resistance. If you see one that is far different from the rest, you've found the bad one.

Swap coils and see if the problem follows the coil.

Just replace the #7 coil. You must already know that it's almost certainly the issue. Anytime performance is affected by rain/moisture, it's an ignition issue with the coil or wires. Since your truck has no wires, it's the coil by default. So just change it.