Last week I changed the plugs and now it seems the mpg (per the overhead console) have dropped from 15 to 12 mpg. Plugs were the same, RC12MCC4, and other than the gap being up to .050 the old ones looked okay. The truck is a 4.7L 2002 Durango, 115K miles, Airaid intake w/TBS, and 31" AT tires. I've owned the vehicle for 30K, and this is the first plug change that I have done. I live in PHX, and although its 105 I haven't seen a drop like this for the last 3 years. Can I trust the overhead, or should I manually divide the miles into the tank to know how I'm doing? Reseting give me the same results.

 

If all you did is change the spark plugs then I think I found your answer. Your gap is to large. It should be .040. Try this and see if it fixes the problem.

 

Exact same thing happened on my truck when I changed out the plugs!

 

Quote:

If all you did is change the spark plugs then I think I found your answer. Your gap is to large. It should be .040. Try this and see if it fixes the problem

Reply:

I was really carefull to set the gap of the new plugs to the recommended .040, some of the old ones had grown to .050.

 

Welcome to the site. The guys in the first generation Durango section would be able to help you further,
FF

Edit: do not use platinum plugs.....