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:
MegaSquirt-I PCBv3.57 Mods Required: \
That’s it! |
Using the MS-II PCBv3 or V3.57 ECU
(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 color | Purpose |
| Black / White | 12 volt power |
| Black | Ground |
| Brown / Yellow | CKP signal (MegaSquirt pin 24) |
| Blue | TDC 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:
- MegaSquirt-I V3.0 kit
- MegaSquirt-I V3.57 assembled unit
- MegaSquirt-II V3.0 kit
- MegaSquirt-II V3.57 assembled unit
Mod kits discussed in this article:
- MK-BIP373 for ignition control
- MK-Pullup will provide the pullup resistor needed for the internal mods described above
Other recommended parts
- V2.2 Stimulator kit or assembled Stimulator
- 12′ wiring harness or 18″ wiring pigtail
- GM open element IAT sensor
- 3/8″ NPT bung in aluminum or stainless steel
- 6′ DB9 tuning cable
- USB adapter
- Wideband O2 sensor system
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.