How to MegaSquirt Your Nissan 240SX

MSPNP ALERT!

Check out our out‑of‑the‑box plug‑and‑play ECU for 1989–1998 Nissan 240SX. It plugs into the factory harness, typical install is about an hour, and it’s ready to run with no wiring changes.
Link: MSPNP2 Gen 2 Nissan 240SX

Upgrade your Distributors Trigger Wheel

Many Nissans used a distributor or CAS with a set of four or six inner slits and 360 outer slits. Current MS3 firmware supports the SR20DET, RB series, and VG30DE/DETT trigger wheels, but MS1 and MS2 are only able to use this type of trigger wheel for a basic distributor. To get around this limitation, we’ve come up with a set of bolt in trigger wheels for many Nissan applications, including the L28ET, VG30E / VG30ET, KA24E / KA24DE, and SR20DE / SR20DET.

ECU Modifications

Using the MS-II PCBv3 ECU

  • Build the ECU up to trigger from the Hall/Optical Input (all of our MS230-C and MS2357-C units are by default configured this way, too.).
  • We will need a 12 volt pull up on the ignition input. Solder a 1K resistor between S12 and TachSelect (for a V3.0 board) or pin 3 of the JP1 jumper (for a V3.57 board). It’s best to wrap this resistor in heat shrink tubing and put it on the underside of the board.
  • To use the stock ignition module, you just need a jumper from JS10 to IGN (on a V3.0 board) or the center hole of Q16 (for a V3.57 board).

Wiring

The output is quite straightforward – you will just need to connect pin 36 of the MegaSquirt to the white wire on the ignition control module (“Power transistor” on Nissan diagrams). The specifics of the input wiring will depend on which year 240 you have; Nissan changed the wiring colors in 1991. However, the wires serve the same purpose; only the colors changed.  Note that these years apply to the 240SX and are not the same for other KA-powered vehicles.  For example, it appears that some Nissan pickup trucks with the KA24E engine retained the earlier color scheme for considerably longer.

Distributor Wire Colors

’89-’90 ’91 and later Purpose
B/W B/W 12v+
G/B White MS Trigger (to Pin 24 on DB37, or Relay Board TACH terminal)
G/Y Black not used
Black Black Ground

 

Fast idle valves, relays and other components

The 240SX used a thermal type fast idle valve that just needs to be supplied with 12 volt power when the engine is turned on; the fuel pump relay can drive this (and does in Nissan’s factory wiring arrangement). The valve Nissan refers to as the “Air Regulator” will open on its own, so you do not need to set up any sort of idle control with Megasquirt. However, there’s two other fast idle valves on there. One is an on/off valve that opens when the air conditioning is on, which also could be run without the MS.  Nissan calls this the FICD valve. There is yet another IAC valve that works as a PWM valve and can be controlled with our MK-PWMIAC mod kit, refered to as the AAC valve.

The stock Nissan ECCS relay is grounded through a circuit in the ECU. Also, the stock S13 wiring harness is set up to send the injectors 12 volts at all times, even when the ignition is turned off. When converting to Megasquirt, the injectors must not have 12 volt power unless the Megasquirt is also powered up. Sending the injectors 12 volt power with the Megasquirt ECU off can result in damage to the flyback circuits. The wiring diagram below shows one way of modifying the stock wiring so that the ECU and injectors power up at the same time, and also allows the other components drawing power from the ECCS relay to work as normal. Note: The MSPNP uses different injector drivers that shut off on key-off, and has its own circuit for controlling the ECCS relay. These notes on the ECCS relay only apply to traditional MegaSquirts. It does not apply to the MSPNP.

An alternate method of dealing with this is to use the Megasquirt relay board instead of the stock ECCS relay to power the Megasquirt, injectors, and crank angle sensor.

The ECU controls the fuel pump relay; taking this over with Megasquirt is simply a matter of taking the wire from the fuel pump relay to the stock ECU, and running it to the Megasquirt’s pin 37.

The gauges operate on their own, except for the tachometer, which is ECU driven.

While the transmission is connected to the stock ECU, this connection only tells the ECU what gear you’re in if you have a manual transmission. The Megasquirt doesn’t need this connection, and the car should work without this just fine.

TunerStudio Configuration for MS-II

Visit MSExtra.com MS2 Manuals for TunerStudio configutration of MS2.

Set ignition capture to “Falling Edge.”

Important when using the stock power transistor:  On the ‘Ignition Settings’ menu make sure to set ‘Spark Output’ to ‘Going High’ and set ‘Coil Charging Scheme’ to ‘Standard Coil Charge’ when using the mods in this article.