Did switching back to 87 octane just fix my problems!?!?

[Mitchs07explorer]

I don’t know what to think on this! I have babied my Ex ever since I bought it 6 years ago. I had a buddy convince me to run 91 octane in it a couple of years ago versus using 87 octane because it would be “better” for the engine etc... so I ran 91 and didn’t notice a performance gain but I was convinced it was helping keep my engine and injectors clean.

I just had a remann tranny installed a couple of months ago and have not been impressed with the shifts, I’ve never been impressed with the 5r55 transmission as i had my last one rebuilt and now a remann. I’ve reset the computer 3 times doing the proper procedure and just started to think that’s just how a stock 5r55s shifts and it wasn’t going to get any better. My CEL has been on for literally the past year for an p0442 (small evap leak) other than when I clear the code and it stays off between 100 - 200 miles worth of driving and then eventually pops back on.

So we just bought a new house and I’ve really been pinching my pennies. I decided to fill up with 87 octane versus 91 to save myself $5. We drove around for the day and it was driving like it normally does, slightly hard shifts, slightly rough idle but to someone not familiar with how vehicles are supposed to run it would probably feel normal.

The next day I was getting ready to take a 200 mile road trip, I started my car and the first thing I noticed was that my CEL had turned itself off. I proceeded to drive out of my subdivision and immediately noticed how smooth it was shifting. I topped it off with 87 octane and took my trip and it drove fantastic. So far CEL has stayed off and it continues to shift well. Could my issues this whole time be caused by using to high of octane gas!?!?

Upon further research I found that you want to use the recommended octane for your vehicle to get the most out of it unless you have a tuner. I’m just shocked that this could’ve effected my vehicle as much as it did. I’m not 100% convinced that the CEL will stay off considering it was for an evap leak but perhaps the computer was getting a false reading because of the type of gas I was using. Am I crazy!? Is what I’m saying even possible?

 

[Larryjb]

The EVAP code will have nothing to do with the gasoline, so that is likely to come back.

I've always heard that high octane gasoline in an engine designed for 87 will cause carbon build up. There is not enough compression or heat to burn the high octane gas completely.

The only benefit may be in the detergents in the high octane gas, but good quality 87 gas has plenty of detergents. Stick with top tier gasolines and you will be fine.

 

[Mbrooks420]

You also have to watch where you fill up. Most shops don’t sell a lot of premium, so when you fill up with 91 you can get older gas.

 

[donalds]

You also have to watch where you fill up. Most shops don’t sell a lot of premium, so when you fill up with 91 you can get older gas.

Happened to me bad gas had to drain a tank of 93 octane because of bad/old gas the supercharger requires 93 or up so now I only get gas in town at bp or shall

 

[Mitchs07explorer]

I ran what I assumed was premium 91 octane gas for a couple of years. For at least a year of that time I had a canned sct tune uploaded for 91 as well as a shift kit in the tranny and everything was great. Unfortunately I got the dreaded wrench light and since I had the tranny rebuilt once I opted for a remann this go around. Since the install of the remann I decided to return everything to stock after experiencing poor shifting between some of the gears with the sct tune installed. It shifted better after going back to stock but it wasn’t until I filled the tank a couple of times just this last week with 87 that all the hard or jumpy shifting mostly went away. Also I as I mentioned above my CEL is still off. I’m not completely convinced the light will stay off but it’s pretty ironic that the day after I fill up with 87 things start magically working fine again after I’ve been battling some of these issues for so. I’m keeping my fingers crossed lol, I know it doesn’t seem like a plausible cause for all of the issues I was experience but I really think my EX just like regular.