Yes. You have to go back to stock and retune for the 91

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what would happen if you didn't go back to stock before switching it to 91 octane? would I lose my factory tune?

Also what would happen if you upload the 91 octane twice in a row?

 

It won't load the 91 tune fully. And no you won't.

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You can modify your tune or go back to stock then reload the same tune again or load a different tune. Once you load a tune, your factory tune is now stored in your tuner, not in your truck. You won't lose your factory tune by modifying an aftermarket tune you've already installed in your truck.

As for a 91 and 91 back to back upload, you can't overwrite a tune with an identical tune because it no longer exists on your tuner after you have already put that tune in your truck.

And yes, you should go back to stock then load the 91 tune from scratch.

 

Just watch the screen on it. It makes a backup before it writes anything new. I never once went back to stock before switching.

There are redundancies on the i3. You can get the same results with different paths. Drove me nuts. Guess it's the way they wrote the menus.

Like Lew says it takes a few days for the ECM to set the parameters within the tune as you drive. So put 93 oct in on the 91 tune and it will adjust accordingly. Put crappy gas in and it will adjust. It's a tune with different rules not a brand new/different computer all together.

 

So I changed the tune to the 91 octane tune this morning. I don't know if it's related but after a while of driving around town I got a CEL light. P0137 bank 1 sensor 2 low voltage? Went to autozone to get the light checked out and most likely cause is an exhaust leak? I do have an air raid intake tube with kn air filter and magnaflow cat back exhaust? Coukdvthe higher tune be Messing with the 02 sensors?

 

You really need to drive about 150 miles before the new tune settles-in and the ECM completely adjusts to it. So it's at least possible the new tune caused the CEL. I would drive it for a a few days to get your 150 miles then clear the CEL. Maybe it won't come back. If it does, then it was probably just a coincidence.

 

I went ahead and cleared the light with the diablo scan tool and I'll continue to drive and see what happens. Thanks for the help.

 

If he is running the 87 tune and wants to switch to the Diablo tune why would he have to restore his factory tune first? That doesn't make sense. I don't think that's right.

 

I never went to stock to change the octane tune.

I was on the 87 tune for a while then I wanted lew to make my custom tune for 93 so I just went through and tuned it for the diablo tune and drove the 150+ miles lew asked for and sent him the first logs.

No issues and it still restores the actual factory tune fine.

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I'd say that code is a coincidence. I get random TC/Stabilitrac disabled with no CEL yet a P0011 can pos sensor advanced DTC embedded on a scan.I suppose because Lew retarded timing and the ECM got pissed. It's weird. I delete it and go on my way.

Going back and forth between tunes and stock is senseless. Load and go, the computer will figure out the rest because that's its job.

 

Any time I ever tried to switch octane tunes without restoring it to stock it never worked right. You can modify your tune without Turning it back to stock first. But when going with a whole new tune. It's best to restore it to stock and start over.

Also only thing I noticed with the 91 octane tune was my wallet was $10 lighter with ever fill up. Mpg and feel was the same with that or the 87 tune.

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no you do NOT have to go back to stock first... just select the tune you want to use and install/apply it...

 

If he is running the 87 tune and wants to switch to the Diablo tune why would he have to restore his factory tune first? That doesn't make sense. I don't think that's right.

I am kinda with you on this. When i had my duramax and i would swap between my street tune and my tow tune, i never tuned back to stock before swapping to the other tune. This was all done an an efi live autocal but i would think most tuners are the same.