MicroSquirt for driving aux injectors (E85 for direct injection)?

[flyer]

Some direct injection engines have great horsepower potential but they are let down by injectors or high pressure fuel pumps that can not supply the large volume of high octane E85 needed to realize that potential.

Presently the only practical solution is to add a set of port fuel injectors and upgrade the low pressure fuel pump to supply the demands of both injection setups.

Control is the issue. Some stand alone solutions exist but they are more expensive than a MicroSquirt and I bet less powerful.

Alpha N seems like the easy way to do that but I would like to make it a flex fuel setup that can adjust the boost level and fuel volume depending on ethanol content.

There are some simplified aux injector instructions in one if the MegaSquirt FAQs but what kind of setup do I need for a DI car that won't be getting E85 all the time?

My application is a Cobb Accessport tuned Ford EcoBoost engine with an upgraded turbo.

Thanks for the help.

[flyer]

You can use the standard MegaSquirt® EFI Controller to control extra injectors.
You wouldn't need to hook up the coolant temperature sensor, if you didn't want to, you would just set all the temperature dependent values to 100% (warm-up enrichments, cold accel enrich., etc.).
You don't need to hook up a TPS, you can just set all the accel enrichments to 0, and hook a resistor from the input pin (#22) to ground (otherwise the CPU will see a climbing value and go to 'flood clear mode'.)
You don't need to hook up an oxygen sensor, just set the EGO step size to 0%.
For the air temperature sensor, you would just hook a resistor across the pin (#20) where the sensor would normally connect. This resistor could have any value from the sensor curve (in the sensor section of the manual) to approximate whatever temperature you think appropriate, or you could use a potentiometer to tune the extra fuel with a single knob.
There aren't substantial differences in between tuning a piggyback or a stand-alone, except you must remember that you are tuning added fuel over and above what the the OEM ECU is supplying, so you put zeros where you don't want extra fuel (in the VE table, accel enrichments, or wherever).

In theory, you could eliminate some components (mostly a few resistors) from the PCB if doing this, but they are generally so cheap as to not be worth the trouble of omitting.

Of course, you can retain any or all of the standard MegaSquirt® sensors to gain additional control and tune-ability over the extra injectors.

That is from the megasquirt FAQ.

It seems simplistic but I have never tuned with aux injectors, I don't know what will work. Varying ethanol content due to uncommon E85 fill ups is the part that worries me. With straight 91 octane unleaded the boost target should be lower, maybe I need my factory ECU programmed with a high boost target and then with an ethanol content aware MicroSquirt actuating the boost solenoid to enforce a lower target when less ethanol is in the mix?

This type of fuel injection problem is going to be common with more and more turbocharged and direct injected engines in performance cars.

[dontz125]

The uS can accept a frequency signal from a flex fuel sensor. If you want to involve boost control, you need to use the Extra firmware, which has its own forum (click on the MSExtra link at the top of the page). If using closed-loop boost control, you can even use the flex signal to affect the boost targets. Also, with boost involved, Alpha-N (or even Modified Alpha-N) is a lousy way to do it; add a dedicated MAP sensor, and go with Speed Density.

Piggy-backing a MS or uS purely to control aux injectors is easy, since all the ignition, warm-up and idle headaches are being handled by the primary ECU. Looking at the section you quoted, I would add an IAT and (as mentioned) a MAP sensor. Depending on how the car handles when you stomp on the loud pedal, you might want to tap into the TPS signal (it might need an op-amp buffer); adding a second TPS would probably be annoying.

[flyer]

Thank you for the advice.

About that firmware, is there a reason why people wouldn't use it since it seems to add features?

To me the hardware is the thing which is why I have asked here.

Evidently my stock ECU uses the MAF sensor only as a way to measure intake air temps so maybe I have a MAF signal that I can steal. I can add an extra O2 sensor bung for closed loop (wide band). I figure a MicroSquirt would be an ideal way to add sensors and data log things that I can't get from my stock ECU. I will try to borrow signals as much as possible so that I can try to keep the stock ECU and the MicroSquirt on the same page...

What I need is a theory and a plan so I can get the hardware and wiring together before I hand off the tuning to a professional.

[dontz125]

About that firmware, is there a reason why people wouldn't use it since it seems to add features?

One of the smarty-pants comments occasionally made on the Extra forum is to wonder why people still use the B&G code ...

To me the hardware is the thing which is why I have asked here.

Fair enough; the MS2/Extra code works with the MicroSquirt as well. Same processor, so the code is essentially the same, but there are variants to allow for the slightly different pin-out between a boxed MS2 and a uS.

Evidently my stock ECU uses the MAF sensor only as a way to measure intake air temps so maybe I have a MAF signal that I can steal. I can add an extra O2 sensor bung for closed loop (wide band). I figure a MicroSquirt would be an ideal way to add sensors and data log things that I can't get from my stock ECU. I will try to borrow signals as much as possible so that I can try to keep the stock ECU and the MicroSquirt on the same page...

What I need is a theory and a plan so I can get the hardware and wiring together before I hand off the tuning to a professional.

It's a LOT easier to change things on paper and in pixel format than it is in copper and steel! Be careful with sharing sensors; it doesn't take much current sucked into a second ECU to cause the signal to droop, causing both units to read incorrectly. Op-amp buffers are simple devices, and make your sensor readings far more resilient. IATs are simple beasts, and it's sometimes easier to install another. Sharing a biased thermistor generally entails removing the bias resistor from one unit or another, and recalibrating the second unit to use the first's bias value. The B&G MS line comes standard with 2.49 kOhm resistors for GM-type sensors; Fords typically use 27 kOhm resistors.

If you already have a MAF, the uS may be able to read it, so long as you can determine the transfer function.

[flyer]

After reading through MSextra threads going back to 2012, I did not find anything like what I want to do.

Am I the first to think MicroSquirt is the right hardware for adding aux fuel injectors for direct injected engines and E85 fuel?

Until it is as easy to upgrade DI injectors as it is to upgrade port fuel injectors, there are going to be many engines that need to add aux injectors to supply the volume of E85 required to meet their horsepower potential. The biggest reason for this is engine downsizing and turbocharging. It's not going to stop.

Imagine how many people will buy a junkyard direct injected version of the Chevy LS engine and then slap on a port fuel injected intake manifold with huge injectors and boost the hell out of it.

[dontz125]

DI engines are relatively new, and there is still a lot of headscratching going on about how to approach it for the DIY crowd. Same with DBW - established tech for the OEMs, but only tentatively approached by the aftermarket gang. Are you the first to have this exact problem? Yes, but it certainly isn't new ground. You might be the first to consider a MicroSquirt as a piggyback controller for a DI engine, but you aren't the first to contemplate a secondary controller while keeping the OEM box. Not by a decade or two ...

The fact that your engine is DI is almost irrelevant; the OEM ECU controls the main injectors, and that's quite common. All you're doing is adding fuel based on boost and flex %, and that's well within the capabilities of the uS. Tuning will need to be carefully done, adding in fuel via the port injectors as the DI injectors run out of capacity, but your plan of dyno time with a proper WBO2 sensor sounds entirely reasonable.

Before the mods get mad at us, I suggest talking this over to MSExtra, where I'm sure lots of other folks would be delighted to chime in!