Tuning for E85
In this section we will discuss the basics of tuning with E85 and the reasons why several tunes may be necessary to successfully utilize E85 all year round. The following concepts are based on the three classes of fuel available and how each concentration affects the tune. This discussion assumes you have a working knowledge of tuning concepts and implementation and is in no way a guide to tuning your car for E85 consumption but to serve more as a theory of concept and workflow.
It is necessary to understand that our vehicles were not initially designed for E85 consumption and as such, lack the necessary logic to control changes effected by the changing properties of the fuel. This is the very reason it is necessary to re-tune for these different class fuels through out the year. Simply put, our ECU’s are E85 dumb. As previously mentioned, a true flexible fuel vehicle has a sensor installed that reads the ethanol content of the fuel. The ECU translates the value to a percentage of concentration and then is able to correlate that value and make compensations based on fuel composition. This allows a flex fuel vehicle to run any concentration of ethanol from 0% to 100%. We are not that lucky and, if E85 was consistent, it would not make much of a difference at all. Our only constraint would be to either run E85 all the time or Petrol all the time. Since there are three different classes of E85, the issue is slightly more complicated than just tuning for E85 or Petrol. As previously mentioned, E85 remains more consistent in the southern regions where the weather is warmer so it may not be necessary for someone living in Florida or Texas to have multiple tunes. You will need to log through out the year to determine that.
Before we continue it is good to understand the concepts of AFR as it relates to E85. Because E85 contains less energy per volume it is necessary to use more of it to achieve the same desired result. As such the stoichiometric AFR of E85 at an ethanol concentration of 85% is 9.76:1 vs Petrol at 14.7:1.
You might be thinking it is impossible to tune because our ECU’s only read up to an effective 11.2:1 AFR and can only adjust up to that point. This is not so and here is why. All ECU’s and other stand alone AFR gauges designed use a number called Lambda. That number is the same for Petrol as it is for E85 and is equivalent to 1.0 when either fuel is stoich. What this means is that for a value of 1.0 lambda, for what ever fuel you happen to be using at the moment, it will report its result as 14.7 whether it is E85 or not because the lambda is 1.0 and the gauge is calibrated for petrol. That means when running E85 and your AFR is reported to be 14.7, your real-time AFR is 9.76. This is very good news for us because all we would need to do is increase the injector pulse width till our reported AFR’s are ideal for Petrol but while running E85. With the exception of increased injector pulse width, tuning for E85 is no different than tuning for Petrol.
So why the need for several tunes? Because E85 is not at a consistent concentration. Not even with in each class of E85. Also the lack of logic within the ECU prevents the ECU from properly compensating for differences in fuel. Add on top of that the differences in altitude and weather and you escalate the effects even more so than with just petrol.
E85 blends, Effects on Closed Loop Fueling.
Here you would expect the ECU to do its job and compensate for differences in fuel by comparing the target fuel values dictated in the Primary Fuel Tables with the real world conditions as dictated by the various sensors, and making adjustments as observed by viewing Fuel Trims Immediate and Fuel Trims Learned.
Well it does, and quite well up to a point. Your trims will compensate for errors as much as +/-25%. Though I have never personally observed fuel trims to exceed an average 12% as affected by ethanol concentration, it is possible. Many tuners will say an ideal tune is less than +/-6% when Fuel Trim Immediate and Fuel Trim Learned are combined. It is for this reason I like to dial in my closed loop fueling for the particular fuel you are running at the time.
I have observed that when utilizing E85 and running less than ideal fuel trims, the result is a slightly rougher engine idle, some hesitation and overall roughness. The closer to ideal I can make my trims the better everything runs.
These effects multiply when you change altitude or experience extreme climate changes.
E85 blends, Effects on Open Loop Fuel.
Here is where engine damage can occur. Let’s say you are running your car on a class 1 summer blend but have a tune that was derived from a class 3 winter blend. Closed loop fueling will most likely be able to compensate for the difference but when you go wide open throttle and into open loop operation, the ECU is calculating fuel that is dictated by the values set in the primary fuel table and for what ever air flow is observed at the MAF sensor but does not take into consideration readings from the O2 sensor and will mot make adjustments based on that. To put it in simple terms the ECU is deriving fuel based on look up values.
So since the ECU thinks it is calculating for Petrol, it has considered that the fuel remains constant. It thinks all is fine and continues on Fat Dumb and Happy when in actuality the ethanol content in your current actual fuel is much higher than the winter blend you are tuned for and you are now running much leaner due to the fact you are currently tuned for a fuel with higher concentrations of petrol. The risk here is a higher propensity for knock to occur depending on how aggressively you’ve tuned initially for E85. The high levels of octane offer some degree of buffer but I tend to stay on the safe side of the fence.
For closed loop operation, Fuel Trims should be maintained at the same levels of gasoline or even leaner, but for open loop fueling, there are two camps for making power and both are right. The thing to know is when one strategy is better than the other.
Strategy 1 is when using larger turbos, it is better to be richer when speaking in terms of making power provided you can burn all the fuel being injected. The reason why is because you are increasing the mass but to make successful use of the fuel you will need to reduce the timing to allow the fuel to burn more fully and also increase temperatures which will have the side effect if increasing the volume of the exhaust even more. Ultimately the exhaust load will be greater and the turbo will come alive as a result.
Strategy 2 is for smaller turbos that inherently spool quickly. In this scenario it is quite the opposite. You run leaner and make power by increasing timing.
Timing and boost
When tuning timing remember that the MBT for E85 is similar to gasoline in the lower RPM/load range of the table and more advanced for mid and higher RPM/load ranges in the WOT region. The advantage with E85 is there is a greater resistance to knock. So when increasing boost, the timing levels can remain the same and even be increased in the higher load regions. But again you need to decide your ultimate strategy as outlined above. Even though you can increase timing, you need to think about it in terms of what the setup needs to produce power and spool. You will need to experiment to find your best strategy
One other point is that when running an inappropriate tune, during start up, the initial injector pulse widths are not ideal. It will be very difficult to start the engine in the winter time if you have a summer time tune installed and perhaps vice versa.
Tuning Work Flow
These steps assume you have already installed the necessary fuel system upgrades such as bigger injectors and fuel pump as a minimum. It should also be understood that this is only to get you to a base tune status and will require further extensive tuning. Once this base is establish, the subsequent tuning steps are no different than tuning for Petrol.
1.) To start the initial E85 tune you will want to start with a known good Petrol tune that is already pre scaled for the injectors being used first. Start by logging with the petrol tune while running petrol in the tank. This is to derive a base line reference and a starting point for your E85 tune.
2.) Verify the injector scaling and record or note the fuel trim immediate + fuel trim learned while engine is at idle. Combined trims should be less then +/-6% at idle. If not then make adjustments to injector scale till trims are ideal.
3.) Verify both closed loop and open loop fueling throughout the RPM range to be ideal. Make adjustments to MAF scaling if needed and then save the tune. Repeat form step one till trims are ideal.
4.) Now save the Petrol tune as something else. This will be your new base E85 Tune.
5.) Make the switch over to E85
6.) Run the new tune and adjust Fuel Injector scaling and Boost Error Trim by applying a multiplier of 1.30 for an increase of 30% over current.
7.) Install the tune and start the vehicle. Allow it to reach operating temperature. Reset the ECU and start it again.
8.) Allow it to idle and observe the fuel trim immediate and fuel trim learned to stabilize.
9.) Observe fuel trim immediate + fuel trim learned at idle and adjust scaling till combined trims are ideal.
10.) Save your map
11.) Repeat step 7 to 10 till fuel trims are ideal.
Once you have established a base tune you can begin tuning your open loop and closed loop fueling as desired. Also changes to timing and boost can be done as desired and tip-in enrichment will most likely need to be adjusted.
Once tuning is complete, to adjust your tune to accommodate different classes of E85, all one needs to do is fill up with the desired tank of fuel and rescale the injectors till fuel trims are ideal as outlined above.