I recently changed the plugs on my '01 4.7 Dakota, which has 70K on it. The gas mileage has gone down dramatically, from 330 miles per tank to about 170. I did everything correctly, including setting the gaps, and there's no check engine light or rough running or idling. The truck did, however, seem a little sluggish at first.

I put in Bosch plugs, but it had Champions in it before. I also change the oil and filter regularly, as well as a new air filter each time I change the oil. Any thoughts?

Thanks, Alex

 

I know that I put the bosch platnium +4s in my neon, and my milage went down. I have been told that neons don't like "performance" plugs. I put NKgs in and my milage went back to normal.