[Bbearden101]

Like detailed in the topic my 2017 Ecoboost idles rough from time to time I noticed it this time when the tank dropped below 1/2 and I'm pretty sure it was the same scenario last time. It only has 40k on the dash so I know it's probably time for a tune up, but was trying to hold off until next month for that. I had 91 octane in the tank before both fill ups, and put 93 then when the tank got down to 1/2 it started acting funny. Could it be that now my tanks down to 1/2 it's finally pushing straight 93, and the computer is just trying to adjust for that? I filled up at Kum&go this time, the first time I filled up at a Valero so I figured I'd wait a cycle before putting 93 back in it to try and flush the bad gas out if it was that. Like I said it was running fine, and only does this when it drops to around about a half a tank on 93 octane

 

[Bbearden101]

Doubt if it is octane related. When you add half a tank of 93 to a tank that's half full of 91 you end up with a full tank of 92. The gas mixes as you fill it up and drive it so there's no separation of the two.


U.M.

I hooked up a ob2 reader the day after the problem persisted, and again with 93 being ran in my tank it showed a bad gas/too lean fuel code on the scanner. Idk what's going on I've seen a lot of people running 93 in these cars without a problem. The only thing I can think of is maybe it's got a 91 tune? Because I run 91 without a issue and have been running 91 since I bought the car except a couple tanks of 93. On the tune up a couple threads I've read say you should change the spark plugs in these engines or at least check them at 30k https://www.cjponyparts.com/resources/mustang-general-maintenance check out here