I have a 2007 Ford Ranger Sport with the 3.0L engine. Have had it for slightly more than a year, then one day started and had a severe misfire. Turns out is was cylinder 6. Replaced the spark plugs and wires. Seemed to be the cure. Pulled a tent camper about 1500# with no problems. Bought a Mini Max camper at 2300#. Pulled it about 200 miles without any problems, then got the severe misfire again. Disconnected the camper and the truck did great, no problems, but replaced the ignition coil and had the injectors cleaned. Connected the camper again and same severe misfire, only now it was cylinder 1.The tow rating/capacity of the Sport is 2620#. I'm at a loss as to what is causing the misfire. I would think that if the two weight was a problem, it would just not pull good. Without the camper, I can't get it to misfire, hook it up and starts in just a short distance.

Any suggestions on what what the problem might be would be greatly appreciated.

 

Seems to be based on engine strain. With normal load on the engine it's fine but with extra load it isn't. Maybe fuel?