So I have a 2013 XLT 5.0 and I have been noticing the warm idle knock that seems to be prevalent in these engines. Before bringing it to the dealer, I decided to do a little science to my truck.

I decided a few mornings ago to try changing up my fuel to see what happened to the engine sound. I normally use an Irving station, and normally use their regular 87 octane fuel. Instead I added their 89 octane. While the octane rating should have absolutely impact on the engine, it does advertise increased levels of detergents and will also increase the exhaust temperature a little bit. Within 4 days, the warm idle knock went from significant to almost inaudible.

Now this leads me to one of two things:

1) I have a bum knock sensor...
2) Detergents make a significant difference in this engine.

So to further my science, I'm going to start using a top tier fuel (Mobil or Valero in my area) at their regular 87 octane. This should put me at increased detergent levels without paying the price for 89. If the knock comes back, it's probably a bad knock sensor or cam position sensor. If not, I win!

I'll report back over the next few weeks as I see more.

 

A lot of this faint noises heard in the 5.0 at idle are considered normal and they all do it

 

Yeah, this wasn't faint. There's a few videos out there from other people, but the sound is significant.

 

Did it sound like this?

 

Yeah, pretty close. On the passenger's side? Only when warm? Goes away when you hit the gas?

 

It's on a cold start to but goes away when I hit the gas

 

Might be different than mine. Mines always silent when cold. I can still hear it with the different fuel, but it's way quieter so far.

 

Ok I'll try a different fuel and see what happens