Mustang 5.0 MS2 + PNP Adaptor Harness kit

Note: The adapter harness kit is discontinued. This page is for reference for people still using this harness.

You’ve received the MS2 3.57 Mustang PNP kit.  What do you do now?


Step 1: Read, read read!!

All instructions and documentation are available online.  We have a tech article written about the EEC-IV adapter, available here. This will get you familiar with the kit, how the ECU is built, as well as how you would build an unassembled ECU to work with the adapter harness.  The ECU in the Mustang Kit is already preassembled and includes the necessary modifications.  That about covers the first “Read”.  Here are a few more:

Step 2: Download the software package

Now that you’ve become familiar with the process to get started, it’s time to download the tuning software. Check out our downloads area here and grab our most recent software package. Please note that while we try to keep our software packages as up to date as possible, some items receive very frequent updates, for example TunerStudio. Once installed, an update to the software may be required and in most cases will be found and done automatically by TunerStudio.

Step 3: Install your ECU

Disconnect the wiring connector from the factory engine computer and connect the MegaSquirt and PNP cable in its place.  Run a vacuum line from a port on the intake manifold that will see manifold pressure 100% of the time, through the firewall in a location it won’t get pinched, and to the MAP port on the ECU.  Be aware that some ports near the throttle body may get blocked off at various throttle positions.

Step 4: Connect your laptop

  • Create a project in Tuner Studio
  • Verify the COM port number of your serial port or USB adapter
  • Power up the ECU by turning the key to ‘ON’
  • If needed, visit the connection setup page.

Step 5: Calibrate your sensors

Calibrate your TPS, O2, coolant temp, and intake temp sensors to be sure they are giving you correct readings.  These screens can be found under the ‘tools’ menu in TunerStudio.

Both CLT and IAT calibrations:

  • Bias resistor value = 2490


Step 6: Fire it up!!

  • The base tune is for the stock 19 lb/hr injectors. Since this is speed density, it will ignore any attempts to use the MAF to change the fueling, so you will need to adjust the tune if using oversized inejctors. To do this, go to Basic Setup -> Engine Constants, and click the Required Fuel button. Enter your engine and injector size, and click OK. Don’t be alarmed if it defaults to unexpected values – the numbers in the Required Fuel Calculator aren’t stored as part of the tune.
  • Don’t forget to set the base timing.
  • Start some light tuning, perhaps study / learn the fundamentals of tuning EFI yourself.
  • Get the car to a dyno shop for a proper tune.
  • While connected to the ECU, this is a great time to save the tune file.  In TunerStudio, go up to “file –> save as”.  Use a name you can remember, such as “First-Installed.msq”.
  • Make it a habbit to save your tune before you make any changes.  This way if you make a change and don’t like the way the car runs, you can simply reload the tune from before you made the changes.

Common questions

  • How can I add a wideband O2 sensor to it?
    • You’ll need both a wideband O2 sensor and a controller. Nearly all aftermarket wideband controllers have an analog output. You will splice this wire to the wire coming from pin 29 of the EEC-IV harness for the ’86-’93 harness, pin 43 for the ’94-’95. Then you will connect to the ECU using TunerStudio, go to Tools -> Calibrate AFR Table, and enter in the output curve for your  wideband controller.
  • What OEM sensors does this kit use?
    • It uses the TFI distributor Hall sensor, throttle position sensor, coolant temperature sensor, intake air temperature sensor, and the left bank O2 sensor. Some users prefer to replace the factory IAT sensor with a GM version. There is a 2.5 bar MAP sensor built into the MegaSquirt, so it does not use the stock MAP or MAF sensors.
  • How do I scale it for boost?
    • When using the default (speed density) tables, the load % equals your MAP sensor reading in kPa. 100 kPa is (within a few kPa) atmospheric pressure at sea level. You will need to edit the load values to go over 100, and adjust the VE, AFR, and spark values to match.
  • What do I need to add an MSD box, or similar ignition?
    • Just wire it up like you’d install the MSD box on a completely stock Mustang. You can even use MSD’s plug in harness.


What if…

  • … the ECU is unresponsive, won’t connect to your laptop, won’t start the car?  Double check and ensure that the PNP harness is bolted down tight to the factory harness with the 10mm bolt and that the two small screws that hold the DB37 to the ECU are screwed down snug.  If the car runs on the stock EEC-IV ECU, it will run on the MS2 3.57 Mustang kit.  A loose connection can stop everything so be sure each side of the PNP harness is secured tight.
  • … the ECU needs firmware reloaded, or you would like to go back to the default tune file MSQ if you’ve made some changes and don’t favor the results?  We have a walkthrough to reload the firmware available here.  You will want to use MS2Extra 2.1.0P (included in our software download package) if you plan to reuse our basemap again.
    • The tune file in your ECU will not be carried over after a firmware reflash.  To reload the basemap either after a firmware flash or just because, the process is the same.
  1. Connect to the ECU with the tuning software.
  2. In TunerStudio, go up to “file –> open tune”.
  3. Browse to a previously saved MSQ or start over with our 1993-5.0 Mustang Base Map Avaliable Here.
  4. The tuning software will confirm if you wish to load the tune file and burn it to the ECU, say Yes.
  5. It may not be needed, but a power cycle after all info is burned to the ECU is good practice.