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How to MegaSquirt your Chrysler, Dodge, or Mitsubishi 3.0 SOHCUsing the stock distributorUpdated 1/19/2009
Application(s): This article covers the 1988-1995 Mitsubishi / Dodge / Chrysler 3.0 SOHC V6, as used in K-car derived cars (Daytona, LeBaron, Shadow, Sundance, minivans, and other applications) as well as in the Mitsubishi Diamante and various Mitsubishi trucks. Level of control: Parallel installation -- Fuel and Ignition Control. Most users will want to retain the stock computer for things like alternator control, although the Megasquirt is close to acting as a full standalone EMS. For parallel installation tips, see this article. The 3.0 SOHC V6 was a joint venture between Chrysler and Mitsubishi, and is a straightforward engine to MegaSquirt. These engines used a basic optical distributor with two rows of trigger holes. One row, called the low data rate, consists of six equally spaced slots. The other one, called the high data rate, usually contained 360 equally spaced slots except it had 10 consecutive slots missing, making it a 360-10 wheel instead of the common 36-1. A few applications used a row of 4 unequally sized slots in place of the high data rate slots. However, in either case, MegaSquirt only needs the signal from the 6 equally spaced 'low data rate' slots.
ECU ModificationsWith this engine, we recommend MegaSquirt-II. Its stepper IAC motor control can drive the stock idle air control valve, which is one feature MegaSquirt-I does not have. For those looking to build this on a budget and willing to find another way to control idle or give up idle control entirely, we also have a write-up covering MegaSquirt-I.
WiringThe output is quite straightforward - 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 low resolution input signal from the low data rate output pin to the MegaSquirt pin 24. Optical pickup pin out
Idle Air ControlThese engines used a stepper idle air control motor. Chrysler versions used a 4 pin unipolar motor, while the Mitsubishi version has a six pin bipolar motor. Using the bipolar motor requires disconnecting its 12 volt power feed line. If you have a MegaSquirt-II, you can drive the IAC valve from the MegaSquirt pins 25, 27, 29, and 31. Chrysler used a couple different pinouts for IAC valves on these engines; early ones usually use the top version in this drawing, while later ones usually use the middle version.
For the version installed in the Mitsubishi models, we have the pinout information for the 6 wire IAC, but haven't yet determined the exact polarity of the wiring yet. We're confident we can work through it with a volunteer customer that's diving into this and we'll update this article then; just let us know and we'll work through it with you.
Other Things the ECU ControlsThe 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. Cooling fans: The ECU has a single cooling fan output. On the MS2, you can use the on/off IAC output to drive the cooling fan relay. On a MS1, you'll want to add a MK-RelayCtrl for this. Alternator voltage: These cars have the voltage regulator built into the ECU. We recommend leaving the stock ECU in place in a parallel installation so it can still control this. The other option would be converting to an external voltage regulator. 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 if you are leaving the stock ECU to control the alternator, you might as well leave it to control the A/C as well. Tachometer: This is controlled from the stock ECU on many of these vehicles, another reason to go for a parallel installation. Those more willing to experiment might want to try out one of these circuits for MS1/Extra or one of these for MS2/Extra. Automatic transmission: The 41TE has its own controls, but they often talk to the stock ECU. If you have these, this is yet another good reason for a parallel install. If you are leaving the stock computer in control of anything, it's best to give the Megasquirt its own temperature sensors, as sharing these with the stock ECU is tricky.
MegaTune Configuration for MS-IISet 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.
MegaTune Configuration for MS1 ExtraOn 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.
Suggested partsAs stated above, we recommend a MegaSquirt-II 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 if you are removing the stock computer. If you are leaving the stock computer in place, we recommend adding a coolant temperature sensor and an IAT sensor for the Megasquirt. ECU Recommendations:
Mod kits discussed in this article:
Other recommended parts
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