How to MegaSquirt Your Mitsubishi 4G37

Using the stock distributor

Application(s): This article covers the 1990-1994 Mitsubishi 4G37 1.8 SOHC motor, as used in the Eclipse, Talon, and Laser base models.

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

Mitsubishi gave the entry level DSMs a 1.8 liter SOHC motor with slightly different controls than the 4G63s. This article covers how to take full control of this distributor based ignition system. These have a simple triggering system with an optical trigger in the distributor. The outer row of slits has four equally spaced slits, and there is a single inner slit for the second sensor. When you’re using a distributor, you only need the 4 slits in the outer ring, unless you want to get creative and use this to trigger a distributorless ignition. (If you want to try that, you could swap over the 4G63 coil pack and use the 4G63 mods, adjusting the trigger wheel settings by specifying 4 trigger wheel teeth instead of 2, and enabling dual distributor output so as to use wasted spark.)

ECU Modifications

On these engines, you can use either the MegaSquirt I or II. We recommend the V3.0 board if building one yourself, or the V3.57 if buying one ready made.

Using the MS-I PCBv3 with MSnS-E firmwareNote the separate instructions for v3.0 and v3.57 PCBs

MegaSquirt-I PCBv3.0 Mods Required: 

  • This is assuming you are starting with an ECU built up like I build my assembled MS130-C MegaSquirt-I PCB3.0 units.  If you are building your unit up from a kit you can implement these changes during assembly.
  • Flash ECU with MS1/Extra version 029v or later.
  • Install the Hall / optical input circuit (step 50A and 52)
  • We will need a 12 volt pull up on the ignition input. Solder a 1K resistor between S12 and TachSelect. Wrapping the resistor in heat shrink tubing will protect it from accidental shorts.
  • Jumper IGBTOUT to IGN to send to IGBT ignition coil driver signal out of pin 36 on the DB37.
  • Cut out C12 and C30.  (Only needed when triggering from the – terminal of the coil, which you are not)
  • Remove D1 and jumper it, or just install a jumper wire across it’s leads.  (Only needed when triggering from the – terminal of the coil, which you are not)
  • Cut out R57 if fitted (this won’t be there on my units though).
  • Get a 330 ohm 1/4w resistor and cut the leads down to about 1/2″ at each end. Maybe a bit less.
  • Tin each end of the resistor with a bit of solder.
  • Cut a 5″ piece of hookup wire (22ga is fine) and strip just a 1/8″ or so. Tin the stripped wire with solder.
  • Melt the tinned wire tip to one end of the tinned 330 ohm resistor tip and let it cool.
  • Heatshrink wrap this wire/resistor assembly.
  • Use this wire/resistor combo to jumper the ‘top’ (top as in when you facing the silkscreen side of the PCB, with the text so that you can read it normally) lead of R26 to IGBTIN on the opposite side of the PCB.

 

MegaSquirt-I PCBv3.57 Mods Required:  \

  • We will need a 12 volt pull up on the ignition input. Solder a 1K resistor between S12 and pin 3 of the JP1 jumper (for a V3.57 board).
  • Get a 330 ohm 1/4w resistor and cut the leads down to about 1/2″ at each end. Maybe a bit less.
  • Tin each end of the resistor with a bit of solder.
  • Cut a 5″ piece of hookup wire (22ga is fine) and strip just a 1/8″ or so. Tin the stripped wire with solder.
  • Melt the tinned wire tip to one end of the tinned 330 ohm resistor tip and let it cool.
  • Heatshrink wrap this wire/resistor assembly.
  • Run this resistor on a wire combination from the right side of R26 (I know, it’s kind of tough to solder to a surface mount resistor) or pin 7 of the Ul socket (which is a lot easier to solder to) over to IGBTIN.
  • Install a BIP373 transistor in the Q16 slot, using a mica insulator.

That’s it!

Using the MS-II PCBv3 or V3.57 ECU

  • Build the ECU up to trigger from the Hall/Optical Input (all of our MS230-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.
  • The only change is to enable the IGBT High Current Ignition Coil Driver Circuit to directly drive the coil.  (If you’re buying an assembled unit, we’ll gladly do this for you for just a few bucks, shoot us an email)
    • Remove the jumper from JS10 to IGN (on a V3.0 board) or from JS10 to the center hole of Q16 (V3.57) Some MegaSquirts may not have this jumper installed.
    • Jumper IGBTIN to JS10
    • Jumper IGBTOUT to IGN (on a V3.0 board)
    • If Q16 is not fitted, install a BIP373 in the Q16 slot using a mica insulator.

(This will enable the BIP373 Ignition Coil Driver)

That’s it!

Wiring

The output is quite straightforward if using a coil without a built in ignition module – you will just need to connect the negative terminal of the coil to pin 36. The positive terminal is connected to the same switched power source used with the stock ECU. For the input side, wire the CKP input signal from the CKP output pin to the MegaSquirt pin 24.

Wire colors

Wire colorPurpose
Black / White12 volt power
BlackGround
Brown / YellowCKP signal (MegaSquirt pin 24)
BlueTDC signal (not used)

Idle Air Control

These engines used a DC servo motor for idle air control, nobody controls these things in the aftermarket. You’ll need to retrofit a PWM or stepper (MS-II only) idle air control valve if you want to control your idle speed from the ECU.

Other Things the ECU Controls

The stock ECU controls a couple other devices in these cars besides the injectors, ignition, and IAC valve. Here’s what to do about the ones you will need to control.

Fuel pump: This is a standard output on the Megasquirt. Wire the Megasquirt pin 37 to the fuel pump relay wire that went to the stock ECU.

Air conditioning: While the stock ECU controls the air conditioner, you don’t need a computer to make this work. Wiring the A/C request wire running to the ECU to the A/C compressor relay should make this work, although we have not tested this one for ourselves.

On these cars, most of the systems – fans, cruise control, automatic transmissions – operate on their own, without being connected to the ECU.

TunerStudio Configuration for MSnS-E

On the ‘Spark’ menu choose ‘Spark Settings’ and set ‘Spark Output Inverted’ to YES.  It is critical to get the Spark Output Inverted setting correct, as setting this wrong can result in damage to the BIP373 or coil. Dwell settings will depend on the coil used.  A typical rule of thumb is to back off the dwell until you can just barely detect a misfire under lean cruising conditions, then add 0.2 ms of dwell time.

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.

TunerStudio Configuration for MS-II

Set ignition capture to “Falling Edge,” and coil charging to Standard Coil Charging. Dwell will depend on exactly which coil you are using. Cranking trigger time must be set to Calculated. If using MS2/Extra, set the ignition type to Basic Trigger.

Important when using the BIP373:  On the ‘Ignition Settings’ menu make sure to set ‘Spark Output’ to ‘Going High (Inverted)’ and set ‘Coil Charging Scheme’ to ‘Standard Coil Charge’.

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

On these motors, you can use a MegaSquirt I or II. We recommend using a GM open element IAT sensor and removing the air flow meter.

ECU options:

Mod kits discussed in this article:

  • MK-BIP373 if you are using a V3.57 board
  • MK-Pullup will provide the pullup resistor needed for the internal mods described above

Other recommended parts

 

Making Your Order Easy

We’ve taken the above list of suggestions a step further, and used it to create two single part#’s you can order by to get everything you need, either in kit or assemble form.  So all you need to answer is, are you a hardcore DIY Build-It-Yourself from a kit kind of guy?  Or would you like it to arrive prebuilt, with all hardware mods completed, and ready to wire up with all the accessories you’ll need?  (we’ll even toss in a free t-shirt)

Note we left a Wideband O2 System OUT of these packages to keep your initial cost down, but as with any engine management system you’ll definitely appreciate a wideband system during tuning.  We highly recommend the Innovate LC-2 with or without a gauge.

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Feedback welcome

If you have any further information, contributions, or questions about this article, please contact us. We’d be especially interested if you have information about using the stock ignition module on these cars, or have pictures you would like to contribute.