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E85 Fuel, Auxiliary Injectors, Split Second Controller (R4)??

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I've modified my (track only, 1/4 mile, dragstrip) 2.3L Ecoboost Mustang to run on E85 ethanol fuel, I added secondary port injectors and a Split Second R4 controller. The car still runs the factory ECU (Cobb tuned, stage 3 mods).

I'm curious, is anyone else using this setup?

The R4 controller doesn't open the secondary port injectors till 3,000 rpm?? Does anyone know why it is programmed like this and what changes I should make?

My 60' ETs were 1.8s on E25 and are now over 2.0 on E85!??

Generally speaking you'll need to tune the system rather than installing and go. Changes required may include RPM, minimum pulse width, how quickly you ramp fuel in with MAP (depending on unit you got), and you'll likely also need to adjust the factory ECU tune as well so the total fuel delivered is appropriate.

"R4 map "

Couple things, my fuel map is set zero blow 3,000 rpm and zero below 2.9 volts.

The controller is also set to 2 cylinder/2 cycle, just like it is an upstream single injector system. But it controls an auxiliary E85 port Injection system.

Is this normal or do I need to make adjustments?

Great question.

You have a 4 cylinder 4 cycle engine, and I think you're planning to use one injector per cylinder.

Based on that you were probably thinking 4 cylinder 4 cycle would be the appropriate setting.

Confusingly, 2 cylinder 2 cycle is how that gets set on that unit in your application.


Should I expand the Fuel Map to include the lower RPMs?

Attached Files

Generally speaking I would start with a fully tuned setup without any aux injection, that is operating within the limits of the stock DI system.

When someone has an integrated standalone ECU solution with DI+PI injection it gets tuned like a single fuel system, aside from divvying up the total fuel requirement between the DI and PI systems and a few compensations, so it's quite straight forward, and airflow/VE don't need to be skewed to achieve goals.

In a stock ECU + piggyback PI situation like yours, airflow, load, estimated torque get skewed, so I suggest starting small with low on times and work in an iterative process of adjusting the piggyback and stock ECU, testing and log review, adding a little more aux injection where needed, adjust stock ECU accordingly, repeat process til done.

I suggest starting by adding a little bit of aux injection only at high load, high RPM, without increasing boost/airflow yet, so you get a feel for the impacts aux injection has. Because you'll be adding fuel the ECU is not expecting, closed loop trimming will go towards negative values. When you tweak your reflash tune to avoid excessive fuel trims it will involve effectively "hiding" airflow and/or reducing VE, which skews tables related to airflow, engine load, and result torque calculations, so generally you want to adjust all those tables so they can still operate properly.

As you add more aux injection, you can blend high injection values down into lower load and RPM areas so the amount injected is never increasing or decreasing abruptly as the engine transitions between RPM and load areas. Ultimately because this isn't an integrated solution, you will be counting on closed loop fueling to do its best to try and reduce the lambda error inherent in this style of aux injection. Modern closed loop trimming does a decent job as long as you don't have any large, step style changes in fuel delivery.

Then as you start increasing boost/airflow beyond what you could achieve without aux injection, keep an eye on DI injection window to ensure you're supplying enough fuel via the aux system, avoiding maxing out the stock DI system.

Like most piggyback systems that aren't fully integrated with the primary engine controller, there will be compromises, but an iterative approach involving tuning both systems a little at a time, will hopefully get you to the result you're hoping for.

Wow! I'm starting to understand what all needs to be done, it's just going to take time and a lot of testing.

Thanks for all the information and help!!

PS: Another odd thing I found in my ECU reflash tunes, is that the desired AFR for the 93 octane tune was set at 14.08 and after I installed the port Injection and switched to E85, the desired AFR was changed to 14.70 ?

You're welcome Don!

Lambda 1.0 on E10 gas (pump gas with 10% ethanol) is 14.08 AFR, so that's where I would expect that value came from.

Lambda 1.0 on E85 is certainly not 14.7, so that's not what I would expect to see based on fuel properties.

Piggyback systems do sometimes lead to decisions outside of normal logic in order to piece things together. Without knowing the tuner's entire strategy, I couldn't guess why they may have done that.

It has me stomped also...!?

On the tune I've put together, I set the AFR to 14.08 and plan on starting with a blended fuel (4 parts 93 octane and 1 part E85), similar to what I ran when running a stage 3 OTS tune from Cobb. I've also extended the rod of my wastegate actuator, to keep the boost under 24 lbs. I'll bring everything up slowly, with a goal of running full E85 and around 26lbs of boost.

I've never built or tuned a car without a carburetor and a distributor, so I have a lot to learn.

Thanks again for helping!! I hope to start testing in 2 weeks, so I'm sure I'll have more questions!

Attached Files


Good luck!

If your gas is 10% ethanol, and the E85 used is actually 85% ethanol, then a 4:1 ratio would give you a 25% ethanol mix, which has a stoich ratio of about 13.01.

Aux injection aside, setting your stoich point based on the properties of the fuel in the tank should improve results. If you use 14.08 when the stoich point is 13.01, you'll have to fudge something to get fuel on target under all conditions including cranking, idle, cruise, and higher load conditions. If you get fueling on target by skewing airflow i.e. MAF scaling or SD adjustment, that has cascading effects on other systems whereas changing the stoich point setting for a fuel simply delivers the appropriate amount of fuel based on the change in chemistry of the fuel, without impacting airflow, torque, etc.

Thanks! I'll bring it down to 13.01 and log a couple runs.

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