Just sharing. Daily driver L33 with turbo, mildly tuned for the 11psi/11afr/11timing on 93. Stock 99 PCM with HPTuners 2bar OS.

I have a lot of E85 around me and they raised the price of 93 to like 4.60/gal so I decided to try out E85 since it's now about the same effective cost per mile (like 3.39 I think it was).

Since this is a DD, I needed to test out a situation where I couldn't get E85. I don't want to deal with doing the alcohol sensor etc.., I know there's lots of ways to get both fuels to work, that's not what this post is about.

So, with a 1/4 tank of 93 STILL IN THE CAR, I cut my tune to be 9.76 stoic. Changed nothing else (yet). No E85 fuel at all. This was to test what would happen if I needed to use 93 in an emergency. This is probably my only chance to test at guaranteed 100% 93.

Results: With a cold car, it was a little tough to start but it did start "ok" feathering the throttle. My particular tune has the idle cells really fat to begin with because it's helped my sloppy Deka 80's while cold at idle open loop, so that didn't help this cold start. But knowing this, I held the idle up out of those cells and it idled smooth, just long enough to get it into closed loop. My idle is normally 750ish so didn't take much actually. Unadjusted wideband was showing around 10:1 during this time.

Theoretically, in an emergency situation the car will already be warmed up and won't need this initial warmup time.

But, once it hit closed loop, the PCM (as expected) trimmed the hell out of it and actually got it back to where it had FULL fuel control idling and driving. Attaching screenshot of my torque app showing trims and oscillating O2 sensors (although slowly graphed because of all the pids I'm logging LOL). Wideband reported stoic 14.7ish as expected driving and idling (wideband doesn't know, it's just reporting adjusted lambda, I'll fix that later).

So, once in closed loop mode and the trims learned out a bit, car ran beautifully. Had full fuel control and idled I think better although technically it should be the same pulse width. Took it for a short drive and it ran absolutely perfectly. Of course I wouldn't let it hit PE at all, again this is just in emergency situation to get the car home.

Note that I think the PCM normally throws a CEL if trims break I think 25%.. can't remember if mine did or if I have that code turned off not sure. But that code is just a warning. Since I'm able to get full fuel control, anyone else in a similar situation should be at least "close" and I don't see any way this could damage anything (catless that is) even for a long long drive.

So anyone worried about needing to put 93 in their tank with an E85 tune this should give you comfort. Of course your tune needs to run CLOSED LOOP with TRIMS, some people just run E85 open loop I guess. Without the trim correction I don't think I'd want to drive the car, it was pretty bad.

I'm going to run a few tanks of E85 through it and my plan will then be to do the opposite (just out of curiosity), put the 93 tune back with pure E85 in the tank. I'd expect it'd trim it the opposite way the same amount and run fine. I'll try to post here and share that as well.

Might be placebo effect, but at idle it seemed to hold that 14.7 afr way more tightly than the 93 tune for some reason