Fuel LTFT's

[Bloody_Booger]

When mixing e30 at the pump are positive LTFT's an indication of higher e85 content or higher 91 content?

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[Dialcaliper]

Took me a bit to wrap my head around this.

Ethanol contains extra oxygen, and so the same amount of fuel burned will show as leaner than expected at the O2 sensor

Positive long term fuel trims mean the ecu is scaling up the injector pulse, aka adding more fuel to counteract a lean condition.

So I would think that barring some other issue, too much Ethanol would cause increased fuel trim in order to end up with a richer detected AFR

One of the tuners can correct me if I’m wrong, but I was under the impression that the off-the-shelf E30 tunes are slightly conservative in fuel and timing in order to account for variation in mixing because E85 is marketing for 51-85% ethanol blends). Warm places typically get the full 85% most of the year, but anywhere cold will drop to somewhere around 70% ethanol blends for winter months, because higher blends can be difficult to vaporize in cold intake air, which mostly means it’ll be harder to start the engine from cold.

In other words, if you’re blending with true 85%, mildly positive fuel trim might be normal, especially if your regular 91/93 contains the full 10% ethanol that is present in some states.