Plug-N-Play Standalone Engine Management System

MegaSquirt PNP Gen2 Documentation

Model/Vehicle Specific information for model MSPNP-MM9093 on a 1990-1993 Mazda Miata 1.6L

Please read all documentation before installing your MegaSquirtPNP EMS, and verify you've followed all steps before starting your engine for the first time.

Physical Installation

  1. Remove the ST SIGN fuse from the underhood fuse box. You should not put it back in when you finish installation.  Do not run the MSPNP with this fuse in place, ever. We've beefed up the Gen 2 MSPNP so it is less likely to be damaged by failing to remove the fuse, but it is not intended to be run like this.

     ST SIGN fuse

  2. Remove the right hand door trim panel. Pull back the carpet to expose the ECU cover panel at the front of the foot well.

    Remove the door trim. Pull back carpet to reveal the ECU cover panel.

  3. Unbolt the ECU cover panel. It's held in place with four nuts and a bolt at the top right. The same screws that hold the ECU cover panel in place hold the ECU to its mounts, so the ECU can now lift out.

    Removing the ECU cover

  4. There's a small pop-in fastener holding the harness to the ECU frame that will come out when you squeeze it. Needle nose pliers will help with removing this.

    Remove the harness fastener.

  5. Remove the wiring harness from the ECU. The easiest way to do this is to push down on the release tab with your finger, while GENTLY prying the connector from the opposite side out of the ECU. Do this carefully and you'll do no damage to your stock harness or ECU.

    Remove the harness.

  6. Now it is time to route the MAP line. Mazda happens to have provided a plug behind the windshield washer reservoir that's about the perfect size for the MAP hose.

    This plug is a good location to run the MAP line.

  7. Pop the plug out and drill a hole in it. The hole should be just large enough to run the hose through. Don't use a knife like we did; carefully use a drill bit. If you use a knife and cut yourself then ‘we told you so'.

    Put a hole in the grommet.

  8. Run the hose halfway through the plug. (pull about 3-4' of it through)

    Hose through grommet

  9. This next step is much easier if you have two people, one feeding the hose in from the engine compartment side and the other one pulling from the passenger compartment. Feed the hose in through the hole in the engine compartment. Have someone else reach up behind the firewall insulation and feel for the hole; it's about as far to the right as it's possible to reach. You will probably find the hose before you find the hole. Pull the hose in through the firewall far enough to reach the MSPNP MAP sensor hole.

    1. From the engine side, stick a screwdriver thru the hole pointing down, use it to push the insulation back a bit.

    2. From inside have someone feel behind the insulation for the screwdriver, this will help them to locate the hole.

    3. From the engine side, remove the screwdriver and push the hose thru the hole and down. Feed it thru while someone pulls it thru from the inside.

      Feed line through firewall.

  10. Pop the plug back into the firewall and attach the hose to the MSPNP.

  11. Route the hose under the hood to the front of the intake manifold. You will need to make sure the hose does not have any chance to catch in the throttle linkage, pulleys, and belts, and make sure it's not pinched by the headlight mechanism when they're raised or lowered. Basically remove extra slack and make sure to avoid any moving parts. This blue line shows a suggested route.

    Suggested hose routing

  12. Cut the MAP hose to length and connect it to the nipple behind the throttle body as shown. If you have cruise control, you will need to cut the cruise control line and use the provided ‘Y' fitting to attach the MAP line.  Note that on some cars, we've seen a more stable MAP signal reading if you tee off the fuel pressure regulator at the rear of the manifold.  If you experience an unsteady MAP signal, try relocating the MAP sensor line to this point.

    Vacuum port

  13. Plug the wiring harness into the MSPNP.

  14. Drill holes in the floorboard and bolt the MSPNP to the floor with the provided sheet metal screws.

  15. Connect the tuning cable to the MSPNP and route it under the transmission tunnel trim or another place that will let you reach it for tuning.

  16. Reinstall the ECU cover panel and the carpet.

At this point, it is safe to power the ECU up, but please make sure you load the appropriate startup map for your specific engine before attempting to start the vehicle.  Using the wrong startup map may result in a no-start condition, or even engine damage if the engine is driven hard before the correct map is loaded.

Verifying and Adjusting Base Timing

Once the MSPNP is installed, it is mandatory to check timing on Miatas. First, put the MSPNP in fixed timing mode by going to Ignition Settings -> Ignition Options/Decoder Wheel (For v1.2 MSPNP2s, go to Basic Setup -> More Ignition Settings). Set Fixed Advance to "Fixed Timing", set Timing for Fixed Advance to 10 degrees, and click the Burn button.

While you can adjust the timing in the same manner as you would with a stock ECU, by adjusting the cam angle sensor, MSPNP gives you another option: adjust the trigger angle within TunerStudio under the spark settings. Increase the trigger angle to retard the spark, or decrease it to advance the spark. Adjust the number until the timing is at 10 degrees. TunerStudio lets you adjust the trigger angle from 0 to 20 degrees. If the trigger angle is out of this range, you should rotate the cam angle sensor to give you more trigger angle.

Using a timing lightCam angle sensor on '90-'93 Miata.

The above picture shows the location of the cam angle sensor for adjusting the timing the conventional way or if you need to adjust the sensor to obtain a better trigger angle. Use a 12 mm wrench to loosen the bolt holding the sensor in place so you can adjust the sensor position. If you use this method for adjusting the timing advance, set the trigger angle to 10 degrees in TunerStudio and turn the cam angle sensor until the timing is at a steady 10 degrees BTDC, then lock the cam angle sensor back down there and check the timing with the light to make sure the CAS didn't slip. If you run out of adjustment, use the trigger angle setting in TunerStudio to get the correct timing.

The timing marks are on the front of the engine. The timing mark on the crank pulley may be hard to see; a dab of white paint down inside the mark (wipe off the excess) can help here. Once you have adjusted the trigger angle and/or cam angle sensor to get 10 degrees BTDC, turn off the fixed timing mode by changing the Fixed Timing setting to "Use Table." 

Timing marks.


Fan control

Your MSPNP is set up to use Output 1 (Formerly ALED) for fan control, under Boost/Advnaced -> Programmable On/Off Settings (for v1.2 MSPNP2s, select Extended -> Output Port Settings).  The fan will come on whenever this output is on.  Note that if the factory thermoswitch is plugged in, the thermoswitch can also activate the fan whether the MSPNP has commanded it to turn on or not, and vice versa - an "on" command from either the MSPNP or the thermoswitch will override an "off" command from the other.

Removing the Vane Air Flow Meter

Since the MSPNP is speed density, you don't need to have the restictive factory air flow meter in place.  We've found gains of 3 to 5 horsepower by replacing the air flow meter with a length of straight pipe.  This does require one wiring change, as there's an air temperature sensor in there.  You'll need to substitute a GM IAT sensor with the air flow meter gone. This sensor connects to the first and sixth pins on the IAT connector, as shown in the graphic below. IAT sensors have no polarity, so it does not matter which wire you connect to which pin.

IAT sensor plugged into stock Miata connector.

Simply wire a GM Open Element IAT Sensor into your factory wiring harness at the AFM connector.  You can poke wires into the AFM connector, or you can cut and splice.  Wire one lead of the GM Sensor to the first wire at the AFM Connector, and the other lead of the GM Sensor to the sixth wire at the AFM Connector. The wires should then be folded down over the edge of the AFM connector, and the whole assembly firmly and cleanly wrapped in high quality electrical tape sealing it up. 3M has tapes, such as Super88, that can handle the temps found in engine bays.

After installing the IAT, turn the ignition key on but do not start the engine. Connect to the MSPNP with TunerStudio. Go to the Tools menu and select Calibrate Thermistor Tables.  Select Air Temperature Sensor.  Select GM from the Common Sensor Values drop down box.  Leave the bias resistor setting at 2490.0 ohms.  Click Write to Controller.  This will update the sensor calibration in the MSPNP.

The IAT needs to be located where it will pick up the air temperature after anything in the intake that changes air temperature. So if you are using forced induction, it needs to be downstream of the turbo or supercharger and the intercooler. Here is a picture of an IAT sensor installed in a naturally aspirated car, with a cone filter taking the place of the stock airbox.

IAT behind a cone filter.

And here's a picture of one way to bypass your AFM and still get your air filter on there (using a popular turbo kit and charge pipe kit), and more importantly, it shows you exactly where to weld the IAT bung to measure air temp AFTER the turbo, and AFTER the IC. You need to know the air temp as it's entering the engine, nothing else will do us much good. If you are running forced induction this is critical, the stock IAT sensor in the AFM will not do.

IAT on a turbo Miata.

Note: If you are using the MSPNP with a turbo or supercharger:

After you delete the AFM, install an IAT sensor in the location pictured above which is just before the throttle body inlet.  The IAT needs to measure the air temperature as it's entering the engine, not the ambient air temperature in the engine bay as would be measured by the AFM.  Only by placing the IAT just before the throttle body can an accurate air temperature measurement be taken AFTER the compressor has heated the air, and the intercooler has cooled it.  Accurate air temps are needed for proper fueling and ignition advance calculations.

Installing an aftermarket Variable TPS

Though your vehicle did not come from the factory with a variable throttle position sensor, and a VTPS is not required for most of the features of the MegaSquirt EMS, we did setup the MSPNP-MM9093 to allow you to add variable TPS using the factory wiring harness if you would like to.  No internal modifications are necessary, unlike the Gen 1.  Some features do require a TPS reading, and it can also help with properly dialing in your acceleration enrichments (though your MSPNP by default will use the MAP signal for this, sometimes TPS based AE is easier to tune).

 Here is the pinout to use if you wish to convert to a variable TPS.

  Function ECU connector pin TPS connector pin Wire color  
  TPS signal 2L 1 Green / White  
  Ground 2C 2 Black / Green  
  5 volt reference voltage 1N 3 Red  

If you're not sure which connection on your TPS goes to which wire, check it with an ohmmeter/multimeter. Observe the resistance as the throttle opens and closes. Each pair of pins will behave differently:

  • The resistance between the 5 volt and ground pins will remain constant.

  • The resistance between the ground and signal pins will be low with the throttle closed and high with the throttle wide open.

  • The resistance between the 5 volt and signal pins will be high with the throttle closed and low with the throttle wide open.

Using these rules, you can establish which pin on the TPS goes to which wire. Note that we have not been able to find a TPS that plugs directly into the factory wiring and matches both the plug and the pinout, so you will need to do a bit of splicing to make this OPTIONAL modification.

Once you have the TPS installed, remove the top cover of the MSPNP2.  It's secured in place with 4 philips head screws.  Locate the jumper labelled "Variable TPS Enable", also referred to as J5.  Note, the silk screen printing may be somewhat obsured.  Install a pull-off jumper in this location, then reinstall the top cover.

Connect to the MSPNP with the key on and the engine off.  Go to the Tools menu and select Calibrate TPS.  With your foot off the throttle, click the "Get Current" button next to the "Closed throttle ADC count" line.  Then hold the accelerator to the floor and click the "Get Current" button next to the "Full throttle ADC count" line.  The maximum reading is 1023 and the minimum reading is 0, but it's rare for a TPS to cover the entire range.  It's more common to see the closed throttle reading in the 0 to 300 range and the full throttle in the 700 to 1000 range, but as long as the full throttle is more than the closed throttle by 200 counts or more, the TPS is functional.  If the full throttle count is less than the closed throttle count, switch the ground and reference voltage wires.  Once you have obtained adequate numbers, click the Accept button and it will save the values to the ECU.

Sequential Injection

The MSPNP-MM9093 is capable of sequential injection. '93 California models are already set up for this; all others must have their wiring harness repinned at the ECU to use this feature. You will need to wire up the injectors using this pinout for '90-'92 and '93 Federal models.


  Cylinder ECU pin  
  1 2U  
  2 2V  
  3 2Y  
  4 2Z  

To enable sequential injection, go to the Basic/Load Settings -> Engine and Sequential Settings (for v1.2 MSPNP2s, go to Advanced -> Sequential Injection), and set Sequential Injection to "Sequential / Semi-Sequential." Click Burn, and turn the MSPNP off and back on again.

Sensor Calibration

If you need to recalibrate your temperature sensors, such as after loading firmware, here are the values to use for the stock sensors. These work for both factory CLT and IAT sensors.  GM IAT sensors can use the defaults in TunerStudio


Temperature (degrees F) Temperature (degrees C) Resistance (Ohms)
  -4 -20 16150  
  104 40 1150  
  176 80 330  

Auxiliary Outputs

  Output Function State Condition (Default)  
  Output 2 (Formerly WLED) -Unused-      
  Output 1 (Formerly ALED) Cooling Fan ON CLT > 190  

Optional Configurations

Several jumpers are located on the lower, black circuit board inside the MSPNP.  These are accessible by removing the top cover and are indicated as depicted below:

Default settings indicated in red.

J4:  Connector J3, Pin 4S Function
When a jumper is installed between the center pin and "A/C FAN", the A/C condenser fan will be turned on when the air conditioning compressor is on.
When a jumper is installed between the center pin and "VICS", the VICS butterflies will be controlled by the MSPNP's Output 2 (Formerly WLED) setting (FWD cars only).

J5:  Variable TPS Enable
When this jumper is installed, it allows the use of a variable TPS.  This should be installed on 94-95 Miatas and 90-93 Miatas with a modified TPS that generates a variable signal.

J6:  Tach Out on Connector J3, Pin 4I (1995.5+ Miata Only)
Unused on this model.

J7:  Sensor Ground Selection
In almost all cases, the jumper should be left installed between the center pin and "Signal Ground".  However, the option is given to allow the engine sensors to be grounded directly to the chassis.

J8:  Cooling Fan Control (1.6L Miata Only)
When this jumper is installed, the MSPNP will control the main cooling fan.  If this jumper is left off, the thermoswitch located on the thermostat housing will automatically cycle the cooling fan.

5-7-20 - 1.4


The EFI Tuners Guide

A Free Education In Electronic Fuel Injection and Ignition Control - How to Plan, Install, Configure and Tune your Standalone EMS!


The MegaSquirtPNP, as with any programmable engine management system, may not
be legal for use on pollution controlled vehicles and is therefore produced and sold for off road/race use only. Check federal/local laws.

MegaSquirtPNP, MSPNP, MegaSquirt PNP, and MS PNP, are trademarks of Hoffmann Innovations, Inc d/b/a