How to MegaSquirt Your Nissan Skyline RB25DET (or Other RBs)

Application(s): Nissan Skyline RB motors with the OEM distributorless ignition.

Level of control:  Full Standalone EMS– Fuel and Ignition Control

The Nissan RB series was never sold in the United States, but it’s been a popular engine to swap into 240SXs and other cars. The cam angle sensor has often been a bit of an issue for MegaSquirt, but now the MS3, you don’t have to disassemble the CAS for an alternate trigger wheel – you can use all stock hardware!

ECU Configuration

We recommend the MegaSquirt-III for its support of the stock cam angle sensor.

Using the MS-III PCBv3.0 or V3.57 ECU with MS3X

  • In step 22, install the stepper IAC jumpers (all of our assembled MS3 units are by default configured this way).
  • Build the ECU up to trigger for inverted VR output. On a V3.0, wire TachSelect to VRIN and TSEL to VROUTINV. On a V3.57, put main board JP1 in the 1-2 position and J1 in the 5-6 position. (Note – this is the standard way our MS3 V3.57 is built.)

That’s it!

MS3X Wiring

Usually, the MS3X uses pin 32 for the cam input signal. Because of the high frequency of the stock CAS, you’ll be using PT4 (pin 31) instead.

CAS pin out

Pin Purpose
A Low Resolution / 120 Degree Signal (MS Pin 24)
B High Resolution / 1 Degree Signal (MS3X pin 31)
C 12 volt power
D Ground

You will also need to connect 1K ohm, 1/4 watt resistors from TPS VREF (pin 26) to both the low resolution signal and the high resolution signal to provide a pull-up in the wiring harness.

For the fuel and spark outputs, use the following pins. RBs came with several different ignitions over the years. Earlier ones used an ignition module which wires to the MS3X. Later ones used logic level coils that connect directly to the MS3X. If you aren’t sure which sort of coils you have, count the pins and check them with a multimeter. Any coil with two wires will require direct coil control. If the coil has three or more terminals and uses power, signal, and ground wires, it may be a logic level coil or require direct coil control. You can check this by applying power and ground to the appropriate wires. If you see 12 volts on the signal wires with the coil powered up, it is almost certainly one that requires direct coil control. If you have zero volts on the signal wire, it is a logic level coil.

MS3X injector pin MS3X spark pin Letter Cylinder
19 14 A 1
16 33 B 5
13 15 C 3
10 34 D 6
7 35 E 2
4 36 F 4

These engines use PWM idle control and boost control, both of which can be done using the MS3X medium current outputs.

TunerStudio Configuration for MS3X

Under the ignition setup menu, set the following.

  • Spark mode: Nissan RB25
  • Trigger Angle / Offset: 0 (adjust as needed if your timing doesn’t line up)
  • Ignition input capture: Rising edge
  • Spark output: Going High / Inverted if using stock ignition module
  • Number of coils: Coil on plug
  • Spark hardware in use: MS3X spark
  • Cam input: MS3X

If you use someone else’s .msq file we do recommend you check the firmware version the .msq file was built on as you cannot always use a file built on one firmware version with an ECU running a different version– it’s best to use the .msq files with the same version of the firmware that the file was built on.  Alternately you can manually copy the settings over from the borrowed file.

Suggested parts

As stated above, we recommend a MegaSquirt-III V3.0 or V3.57 to have full control over the engine. You will be able to use your existing sensors except for the MAP sensor which is built into the MegaSquirt.

ECU options:

Other recommended parts

Additional Ignition System Information

Are you having trouble with your factory RB25 ignition system? Check out this very helpful diagnostic guide that the folks at Pro Street Online put together: https://my.prostreetonline.com/2014/08/11/how-to-service-your-rb25-ignition-system/