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Was running late for work when the gas light came on. So I put a $40 super in my evo cause that's all the closest gas station had. After 10 mins the CEL came on. It threw a P0170 error. Looking at the STFT and LTFT, they were all maxed out at -25% and -12.5% respectively; with the exception of the High LTFT since I didn't push the car with super. Normally my fuel trims all are less than ±3%.

Has anyone else had this experience?
Is my Lambda or MAF failing?

FWIW; I changed my Narrow Band Lamda (O2) sensor and rescaled my injectors on both super and premium. I believe that the composition of Super is so significantly different to premium that it warranted using an alternate fuel map with a different injector scaling.

±3% is impressive...good scaling/latency settings. You are a patient tuner.

Last I checked super in Trinidad is still unleaded, correct? An O2 sensor is not cheap. Was the original sensor pretty old?

Alternatively you could have first rescaled the injectors to see if you could get your trims within ± 5% range with new scaling and latency values.

If successful the O2 was fine and all you needed was an alt "super" map for emergencies. Note that your timing maps would likely have to be revised as you transition from closed to open loop based on the load threshold settings in your map.

I don't doubt the composition of super was so different it justified new fuel settings, but it's pretty rare that you'll only be able to get super in Trinidad unless going behind God back.

I wouldn't use the patient... more like paranoid tuner. Getting the trims close to 5% was quick and easy. Getting all 3 trims under 3% is a PITA. I got a Walker o2 sensor of Amazon with the original harness for around 50USD which a lot less that the OEM one for 300USD. Seeing as I had to splice and lengthen the cable, if I had to do it again, I'd get a BOSH universal type for about the same price though there's nothing wrong with the walker.

After speaking with a former employee of the company that blends the fuel locally and factoring some O'level chemistry, its easy to see the the caloric content of super and premium would be different. The legal requirements are centered around octane. Basically MTBE is used to "adjust" the octane. It also explains why fuel economy (distance per volume) is noticeably better with super.

R. Mutt wrote:±3% is impressive...good scaling/latency settings. You are a patient tuner.

Last I checked super in Trinidad is still unleaded, correct? An O2 sensor is not cheap. Was the original sensor pretty old?

Alternatively you could have first rescaled the injectors to see if you could get your trims within ± 5% range with new scaling and latency values.

If successful the O2 was fine and all you needed was an alt "super" map for emergencies. Note that your timing maps would likely have to be revised as you transition from closed to open loop based on the load threshold settings in your map.

I don't doubt the composition of super was so different it justified new fuel settings, but it's pretty rare that you'll only be able to get super in Trinidad unless going behind God back.

It happens.

i never had any big problem with super. the day i cnaged from premium to super the only thing i had to do was tun out some knock, fuel trims were 2% (Low) and -0.3%(Mid), didnt change at all.

try cleaning your MAF, seems to be an issue associated with this