I have a 2011 F150 with the 5.0, 4x4, and 117k miles. I've owned it for over 3 years and bought it with 69k miles on it. I tow my camper with it a handful of times a year, usually never farther then 5 hours away, but most of the time less then 2 hours away. The trailer is 1400 pounds below the towing capacity of the truck. The truck has been dead reliable up to this point and I stay up on all the maintenance. On to the issue at hand.

Best I can recall I started hearing the problem on Tuesday, possibly after filling the truck with gas, but I can't remember if I heard it before hand. I hear a rapid knock sometimes when using part throttle while driving along. Like one would do when coming to a small hill. It doesn't always happen. I hear nothing when starting off from a dead stop for instance. I also don't hear it when I step on it pretty hard. The only time I can consistently make it happen is if I put the transmission in manual mode in a higher gear like 4/5/6 and get on the gas. First thing I did was check the oil, I was about a quart low. It's close to time for my next oil change and this is the first time its been low. Added oil, still doing it. Then I thought about the fact that I JUST put gas in it and wondered if I just got a bad batch. Put in some octane boost just to be safe and nursed the truck home. It made the noise a few times on the way home, about 6 miles away. Half way home the issue seemed to go away, but it doesn't always happen so I can't be sure. I didn't drive the truck to work today, so I'll tinker with it again when I get home this evening. Just looking for other things it might be. Regardless next week I'm going to take the truck to the dealer and have them change the oil and flush the transmission. Thanks for the info.

 

Knocking went away at about half a tank of fuel was used. Filled up with 93 octane at an out of town gas station and it didn’t come back for the rest of the tank of fuel. Filled up two days ago at a different in town gas station and it immediately started the knocking again. So I have no idea what’s happening at this point.

 

Cheap gas, try filling up at a name brand place for the next couple of fill-ups and see if it goes away again.

 

Yeah, always use name brand gas. Cheaper in the long run.