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E85 initial performance after cold start

Ethanol & Flex Fuel Tuning

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I think the Ethanol & Flex Fuel Tuning course didn't cover this particular topic, or then I missed it. What are the key tips for getting nice behaviour out of the engine when it's cold started without preheating? So all components and fuel are cold (say less than 10 °C) and engine coolant temp has not yet risen above 30 °C. I've found just a short time of preheating or letting the engine idle for couple of minutes after startup makes this problem go away. However I'd like to achieve (as close as possible) OEM-like behavior -- regardless of conditions one could just start it up and drive off without hesitation/sputter/misfires.

The problem must be very low vaporization of ethanol at these low temps. As intake valve is also cold and ethanol viscosity is low, I've found in my case injecting to open valve is preferred. I've run on E85 through last winter and have solved cold start problems at least until -10 °C (we didn't have much colder last winter). Here in Finland we've got E85 all year round from petrol station, and eth content sensor seems to read between 78% to 82% regardless of whether it's winter or summer.

The hesitation and misfires occur particularly on lower rev range, when applying light throttle (but accel enrichment isn't applied as TPSdot is zero in practice), MAP in the area of 50-80 kPa, ie taking off right after starting. After hesitation of a second or few seconds, the engine comes back to life and after that it's fine on about static throttle. I've set my afterstart and warmup enrichments so it runs fine with the static conditions, lambda value being usually in ~0,75 range and cold advance of +5° the moment before the hesitation occurs.

I haven't found difference in changing cold advance modifier of these coolant temps within few degrees to either direction. I'm guessing adding more afterstart enrichment would help, but if possible I'd like to avoid running unnecessarily rich on static conditions -- oil contamination is a concern.


This is a tricky topic for us to cover in our webinars, we barely ever see temps lower than 0 deg c. I will ask management if this is something we can work on in the near future. the basics of cold start and first drive off for low temps is pretty much as you have found, a lot of trail and error on each different system of ECU, some have compensations for fuel temp air temp water temp E85 content post start prestart and so on.

Thanks for the question i know i have not answered it but i will pass on your question

Regards Ross


I have a feeling this phenomen might actually be even worse at temps around 0..10°C than in freezing temps. As the latter requires much more enrichment during initial runtime, the need for possible other adjustments is in these "mid-cold" temps.

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