Originally Posted by Jp7
This advice is like telling someone in the year 2014 "start a fire by rubbing 2 sticks together"
Why not just use a match?
Your ECU monitors through closed loop the fuel mixture. It keeps track of how many times the mixture switches from lean to rich. This information is used to trim the fuel map. If the truck is running rich, the injector pulsewidth is reduced. You can see this with a scanner.
much easier than reading a sparkplug.
Ah, the young.
"start a fire by rubbing 2 sticks together", those that forget this will spend a cold night when their technology(or matches) fails them.
Computer controlled systems are way better than "the old systems" but they are not smart.
Spark plugs simply can not lie, and as easy as it is to do it is certainly worth a look.
The fact that the MPG has dropped and there is no CEL(check engine light) mentioned would indicate a leak OR the computer isn't seeing a problem with an over rich mixture, the fuel trims might look just fine on a scanner because computer, or one of it's sensors, is the problem.