Flashing from E85 to 91
 

So today I flashed from E85 to 91. I followed the instructions, ran down the tank till the gas light was on, filled up on 91 then drove a few miles till the E85 was out of the lines then flashed over to my 91 UEL tune.

My LTFT/STFT was fluctuating alot after the flash (which is normal), I understand the ECU is learning but at idle my LTFT was 18.00% so I just putted around town revving below 3K rpm waiting for it to drop. So I drove about 15 miles and my LTFT at idle went from like...

(at idle) 18 -> 15 -> 14 -> 12 in the course of 15 miles or so. Is this normal, perhaps I flashed over too soon & that's why its taking the ECU so long to learn the fuel trims? This seems to be the most reasonable assumption. However I just find it a bit odd because when I flashed over to E85 I followed the same steps & within 5 miles my LTFT/STFT stabilized below 10%.

Is there something I'm not taking into account, anyways I think I'm going to re-flash my 91 UEL tune and hopefully the LTFTs will stabilize.
@steve99 haaaalp :)

So I reflashed to 91 tune again running the latest tune I believe 2.XX

Still seeing issues with LTFT after about 20 miles.

I thought that LTFT was a long term average of STFT, for the most part STFT seems to be normal varying between +/-5. Some occasional spikes... Knock seems to be minimal. AFR looks normal to me I wasn't doing any WOT pulls.

Anyone have some input, maybe @Shiv@Openflash

Here's a 8 mile log, some cruising & town driving.

http://datazap.me/u/phantobe/91-91-t...g=0&data=1-8-9

high ethanol in the 91 fuel?

There were about 1.5 gallons of e85 in the tank when I fueled up on 91.

And yeah, if your 91 has E15, that'll also contribute to it.
Wouldn't bother losing sleep over it.

Yeah I assume its somewhere between 10-15% ethanol.

Should I just keep driving below 3k RPM until fuel trims stabilize?

Just don't know if I should rag on the engine if its seeing such high trims.

Take it easy and fuel up with 91 again if you are so concerned, although more ethanol is good for timing anyway and the trim is actually going down.

+1 on what @s2d4 said especially if your 91 is already E10 you will be running about e20 till you fill up again.

Yeah I'm just going to take it easy, the fuel trims should keep dropping I imagine a few more gallons they should stabilize.

However I'm not sure if I should try to run this tank dry oooooor... Run to about halfway then fill up on 91 again. I think the latter would move things along quicker to lower the ethanol percentage.



Good for timing, bad for fuel trims apparently with a 91 tune. It would be cool if there was a "transition" tune I'm surprised I haven't seen this brought up before. I think ecutek has a transition tune if I remember correctly.

yeah just run it to half and full with 91 again, trims shoupd go down, trims at 10% not a disaster , especially when you have no knock issues.

you trims were ok before ? ie you dont have an exhaust or intake leak or dirty maf sensor from oiled filter.

No issues prior to this fill up.

Unless something happened that I'm unaware of however if there was a leak somewhat I don't think I'd be seeing the afr I'm seeing.

If it was an exhaust leak, you'd notice immidiately. My LT and ST were all out of wack and that's how I knew to change my over pipe gaskets. Sadly, I snapped the studs on the header with *VERY* little pressure, so now I have an exhaust leak that is massive and loud.

guess it's time for that header :( I really wanted to not spend the money right now though.

Over pipe is after the sensors, how is it picking the leak? Is the air being sucked backwards?

So spend $4 and buy a new header stud.