Would it be OK if I changed my gas from unleaded regular to mid grade I believe 89? I've had my truck in the dealership for over a week with what seems to be a spark knock and they said my percentage of ethanol was high at a out 51%. They could never get around to figuring out what it was either but they ran pure 87 through and said it may help it. Any suggestions would be great. 2009 5.4L

 

Aren't these trucks Flex Fuel and able to run E85?

 

It's ok to run 89, but it may or may not fix your problem.

 

I think he has the 5.4. Not sure that it was flex fuel (pretty sure it wasnt), so ethanol that high would be causing some issues. If you have any pumps with ethanol free like the Wawa I have down the street with 89 ethanol free I would top off with that. If not, yes you can just go and get some top tier 93 or 89. Dont cheap out on it, get something decent.

If your engine is knocking, you need a higher octane rating. If you read up on it, higher octane numbers have more anti-knock capability than lower octane numbers.

https://en.wikipedia.org/wiki/Octane_rating

 

I am pretty sure my 2010 5.4 was a flex fuel engine.

 

I don't think it's flex fuel so I'm pretty sure it's not

 

Yeah I just looked it up. I'm wrong, he should be flex fuel. I'm not certain of his engine though, I just glanced at some of his previous post. Helps to have a little info in the signature.

If he is knocking, I would try to log it. A cheap bluetooth OBD adapter and torque on Android will log knock. That or a good tuner like and SCT. I'd be surprised if its really knocking (spark knock).