Out with oppressive tyranny, in with Freedom to Tune.
The MicroSquirt box is an inexpensive and powerful fuel injection controller. It is the little brother to the fully functional MegaSquirt hardware. To reduce footprint and cost, the MicroSquirt platform lacks an IAC Controller and sequential injection control. These are non critical items to the Mercury 60 4S project because races aren’t won at idle. And that’s the only place where those features are relevant.
Software
Like MegaSquirt, the user interfaces with MicroSquirt by a data cable (bluetooth is an option) and a Laptop. TunerStudio is the user interface software used to view data logs and change parameters. Hardware and software user manuals can be found at msextra.com. Buying the Ultra version of TunerStudio gets you AutoTune trim tables, a nice feature.
There are many videos on YouTube that help with tuning and interacting with MicroSquirt and TunerStudio. SloppyMechanics, run by Matt Happel, is a tremendous resource and good for a confidence boost if you get overwhelmed by the science of engine control.
Sensors and Signals
ECU Inputs – What MicroSquirt Wants to See
There are a few environments that piratically all EFI controllers need to measure in order to provide the correct amount of fuel and spark timing. Fortunately, the factory ECU on the Merc 60 4S uses a scheme that the MicroSquirt can be setup to run. There’s tons of information regarding the how and why of fuel injection in the hardware and software manuals linked above.
The inputs needed by MicroSquirt to run the Mercury 60 4S are:
- Crank Position, Variable Reluctance (VR) sensor reading flywheel tone ring.
- Throttle Position, Throttle Position Sensor (TPS) measures throttle blade angle.
- Intake Air Temperature, IAT sensor in intake manifold.
- Intake Pressure, Manifold Absolute Pressure (MAP) sensor in intake manifold.
- Exhaust Oxygen Content, O2 sensor protruding into the exhaust gases.
The outputs from MicroSquirt to the motor are:
- Fuel Injector Voltage Pulse
- Ignition Coil Fire Pulse
There are other inputs and outputs happening but the lists above are bare minimum to run in closed loop. Open loop control means there’s no O2 sensor feedback and the controller is measuring the TPS, IAT and MAP sensors and going to a predetermined table to figure out how much fuel and when to fire the spark plug. That’s how the Mercury 60 4S operates from the factory. Once the tune is well established, it’s a good way to operate but in development, closed loop is helpful.
Coolant temp is often used as a metric for fuel calculations. Once the motor comes up to temp, it is less useful. Idle Air Control is a common output to help maintain a stable idle, especially during warm up. As stated before, there is no IAC driver on MicroSquirt and we don’t want to add it in for the Mercury 60 4S project.
OE Hardware Modifications
Crank Trigger
Although the control scheme that Mercury uses on the 60 4S is similar to MicroSquirt, there are some hardware changes necessary to make MicroSquirt happy. The most obvious is the tone ring that is a part of the flywheel. Referring to the user manual will show that MicroSquirt expects a tone ring to be missing a single tooth. Denoted as 36-1 or 60-1 means that the tone ring is missing a single tooth but would have 36 or 60 if they were all present. The tone ring on the Mercury 60 4S flywheel is a unique 60-6 configuration that has single teeth missing in various locations.
To get to an X-1 arrangement, there are two options available. Turn down the crank trigger teeth on the flywheel and install a new tone ring in it’s location or weld material in the missing tooth locations. Depending on what equipment is available, one option may be more appealing than the other. The flywheel will be out of balance after either operation so be sure to have that addressed. Since the VR sensor detects interruptions in it’s magnetic field, the new tone ring material will need to be steel.
VR sensors are passive in that they don’t require an excitation voltage. The output is proportional to the velocity of the teeth moving through it’s field. Thus, the factory VR Sensor should work with MicroSquirt.
O2 Sensor
Fortunately, there’s an easy place to plumb in a wideband O2 sensor on the Mercury 60 4S motors. Although the hole will need to be enlarged and re-tapped, there’s access to the exhaust gas through the exhaust coolant inspection plate. Considering the exhaust gasses are kept internal to the motor all the way down to the foot, this is a nice surprise.
Throttle Position Sensor
The TPS is on the short list to be exploited. We are currently unaware of the inputs/outputs to this sensor.
Manifold Absolute Pressure
It’s safe to assume that the Mercury 60 4S MAP sensor will be insufficient. A 2 or 3 bar MAP sensor will be necessary to measure boost in the future.
Intake Air Temperature
The factory IAT should work with MicroSquirt but the calibration will need to be determined empirically. Alternatively, a known GM Sensor can be swapped in it’s place for guaranteed success.
Ignition Coils
The wiring harness, among other features, changes in 2012 when they switched to a 2 coil setup. For the 4 coil arrangement in previous years, each coil has 4 electrical wires in it’s plug. Each coil gets 2 grounds and 2 power wires.
- Black – Grounded to the block
- Black/Green Stripe – Grounded in the ECU
- Green/Stripe – Fire pulse from ECU (+5V square wave, 7ms duration)
- Red/White – Coil Power (+12 Volts)
The Green/Stripe wire has a different stripe color for each cylinder. Stripe color to cylinder number is as follows:
- Black Stripe – Cylinder 1
- Red Stripe – Cylinder 2
- Orange Stripe – Cylinder 3
- White Stripe – Cylinder 4
MicroSquirt uses a wasted spark scheme, much like the 2 coil design would in 2012 and later Merc 60 4S motors. Wasted spark fires each spark plug every revolution. Once during the compression stroke, when it’s helpful, and once at the top of the exhaust stroke where it has no impact. This is is a byproduct of simplifying ECU hardware. It would be weight conscious to swap in newer 2012+ coils when swapping to a MicroSquirt ECU. Since the 1 and 4 cylinders and the 2 and 3 cylinders are 360 (of 720 degrees per 4 strokes) out of phase, those are the wasted spark pairs. Consequently, the Green/Stripe wires of those coils will need to be spliced together for MicroSquirt use.