Pumps switching from E85 to E50 for the winter

[Lex]

We got this question a few times and it's relevant to many E85 users in colder climates. As the temperatures drop and pumps switch to less ethanol in the fuel, here's what to watch for:

Keep an eye on two things as you adjust the volume you are adding at each fill up to make up for the lower ethanol content of the fuel:

1. WOT knock. If you start seeing WOT knock that is consistent above 1.0-1.5 that means there isn’t enough ethanol in the mix and more needs to be added. This is especially true if your fuel trims start to move in the negative direction as described in step 2.

2. Fuel trims. Before switching to a new blend take note of your long terms fuel trims (LTFT) from idle up to when they become 0.16 from going into open loop/WOT. Note these trims and use them as a baseline. If you start seeing them become “more positive” that means your ethanol content is increasing compared to the baseline. If that is the case add less E85 per tank. If you see them become more negative that means your ethanol content is decreasing and you should add more E85 at each fill up. Make changes in one gallon increments.

Here is how switching to E50 from E85 will affect your mixing at the pump mathematically. if you want an E30 mix in the tank and were adding 25% E85 and 75% E10 pump fuel before by volume; when you use E50 you will need to have an actual 50/50 mix by volume to get around the same E30 in your tank. So if you know the pump is serving E50, fill using a 50/50 mix.

[Cheapspeed]

Well shit, how much E am I going to have running 50/50??

I have noticed my trims going a little more negative lately.

[RusianKid]

@Lex;

I am not completely understanding the trims; could you please explain more in regard to the 0.16 figure.

My trims are usually 3.xx when I am accelerating at part throttle, and usually -3.xx(sometimes as low as -6.xx) during deceleration while in gear.

I have always considered my conditions with in the norm; please correct me if I am wrong.

[Lex]

Originally Posted by RusianKid @Lex; I am not completely understanding the trims; could you please explain more in regard to the 0.16 figure. My trims are usually 3.xx when I am accelerating at part throttle, and usually -3.xx(sometimes as low as -6.xx) during deceleration while in gear. I have always considered my conditions with in the norm; please correct me if I am wrong.

If the ethanol content in the fuel changes you will start to see trims change. So if you are used to monitoring your trims and KR for example you will start to see a shift in these values that can indicate the ethanol content in the E fuel you are using has changed.

So look for changes in the values and in order to observe changes you need to know your baseline. For example if they are current at +3% and you see them go to -5% in the same learning zone this is the kind of change you are looking for.

[Vansquish]

Originally Posted by RusianKid @Lex; I am not completely understanding the trims; could you please explain more in regard to the 0.16 figure. My trims are usually 3.xx when I am accelerating at part throttle, and usually -3.xx(sometimes as low as -6.xx) during deceleration while in gear. I have always considered my conditions with in the norm; please correct me if I am wrong.

The 0.16 LTFT (actually -0.16) is the "zero" for some first generation cars, particularly MS6s, when they're in open-loop.

[RusianKid]

Originally Posted by Vansquish The 0.16 LTFT (actually -0.16) is the "zero" for some first generation cars, particularly MS6s, when they're in open-loop.

Thank you for the info. I now fully understand this post!

[Lex]

Originally Posted by Vansquish The 0.16 LTFT (actually -0.16) is the "zero" for some first generation cars, particularly MS6s, when they're in open-loop.

It is zero for all generation MazdaSpeeds.

[SparkySparks]

I wonder how this impacts warmer areas, I know the stations I get E85 from all have a sticker on the pump saying "E-85 Minimum 70% Ethanol".

[RusianKid]

@Lex;

Do colder temperatures effect LTFT if we take fuel quality out of the equation?

For example: would LTFT be the same on a 50F day as they were on a 100F day, if the gas is the same?

[Vansquish]

Thanks for the info @Lex;, I was under the impression that GenPu vehicles don't have that offset.

[Lex]

Originally Posted by Vansquish Thanks for the info @Lex;, I was under the impression that GenPu vehicles don't have that offset.

Heh, this is what happens when you train your eyes to scan over thousands of datalogs. You're right, the gen2 does not show -0.16 in the logs. It shows just 0 when in open loop.