[Uncle Meat]

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.


There should be no reason a "tune-up" is necessary at 40K. What does a 40K mile tune-up even involve anyway?


Sounds like you may have some water in your tank. Have you tried running the tank almost dry and then filling up with a full tank of good 93 octane from a Top Tier station?


Valero is a name brand fuel station and their do sell "Top Tier" detergent gasoline, how I would never trust gas from a Kum & Go, Circle K, Kangaroo, 7-11, etc.


U.M.

 

[Uncle Meat]

Around here some (not all) Circle K's and Kangaroo Station actually sell brand name Top Tier Fuel. I regularly stop at a Circle K that sell Shell Gasoline and occasionally stop at a Kanagaroo that sells BP gasoline. I also buy a lot of gas at Costco which is Top Tier gasoline.

Been so long since I've visited any of those establishments I hadn't noticed they started carrying the TT fuels. Nice to know I could hit one up if I needed to.

One thing to consider if you start having fuel problems when the fuel tank is half full is the performance of the right side fuel transfer unit. Mustangs have a double / split bottom fuel tank. Except when the tank is mostly full, fuel has to be transferred from the right side to the left side (where the main pump is located) to completely empty the tank. If the fuel transfer unit isn't performing properly, then it is possible you are actually running low on fuel if the left side of the tank even though the gauge may indicate a half full tank.

Ed

I completely forgot Ford has been doing the dual tank thing since the S197 platform. Great for overall weight balance. Sucks because it complicates the fuel system.

U.M.

 

[Uncle Meat]

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

Tuned for 91 and running 93 won't affect anything, however if you were tuned for 93 and were running 91 that would be a different story.


As for replacing spark plugs at 30K... that's just a marketing ploy to get you to spend your hard earned money needlessly. Ford states the plugs are good for 100K.


U.M.