MegaSquirt for vintage Mopar ignitions
If you haven’t already, please read the ‘disclaimer’ at the top of the parent page here.
Engines covered:
Pre-TBI LA series (small block) V8, all B and RB (big block) V8, and all slant six engines when equipped with electronic distributor
Types of Mopar ignition systems
Chrysler offered these engines with several different distributors. The earliest ones used breaker points. Chrysler made an electronic ignition standard in 1973, which used both a mechanical and vacuum advance. These distributors used a variable reluctor type sensor, much like the later GM HEI and Ford Duraspark. Chrysler began introducing electronic spark timing control in 1976, and by 1977 brought out their infamous Lean Burn system, which used a distributor with no advance mechanisms at all. The Lean Burn system kept the same VR sensor as the earlier systems. This combination of a computer controlled timing on a carbureted engine is something of a rarity in the automotive world.
One thing about Chrysler ignitions that can create a bit of confusion is that Chrysler chose to name their ignition module an Electronic Control Unit. While this shortens to ECU, this is not at all the same sort of ECU as an engine control unit, at least not in its earliest incarnations. Such units as the popular Orange Box are simply ignition modules with no computing capability (the Lean Burn ECUs are another story, as they control ignition timing and some carburetor components).
In 1988, Chrysler introduced a new distributor design along with throttle body injection for some versions of the 318. This one uses a Hall effect sensors similar to the one Chrysler had used in their K-car engine control systems. The 360 soon acquired the same system. When the Magnum engines came out, Chrysler designed yet another ignition triggering system, this time using an eight notch crank trigger and a Hall effect sensor in the distributor with a single tooth trigger. These two distributor systems, along with the points distributors, are outside the scope of this article. Here we will cover the VR sensor based systems, as they are the most commonly retrofitted Chrysler electronic ignition.
Chrysler distributors will physically bolt on to any other engine in the same family: All LA distributors are interchangeable, all slant six distributors are interchangeable, all B distributors are interchangeable, and all RB distributors are interchangeable. It’s even possible to put earlier distributors onto Magnum engines, although the MegaSquirt can run Magnum ignitions too. So when planning a Megasquirt buildup, you can mix and match distributors to get the easiest to configure distributor on the engine of your choice.
Before rolling out the Hall effect distributors, Chrysler built several different variations on their “classic” VR type distributor, not including the number of different advance curves:
- One VR sensor, with mechanical and vacuum advance
- Two VR sensors, with mechanical and vacuum advance
- Two VR sensors, with no advance mechanism
- One VR sensor, with no advance mechanism
Most of the distributors you will see are either of the first or fourth kind, with the remaining two being seldom seen designs used with the earliest versions of the Lean Burn system. When setting up Megasquirt on your Mopar, you can use any of these four types. The most straightforward is the fourth type, with just one VR sensor and no advance mechanism. If your distributor has an advance mechanism, you must lock out the mechanical advance and disconnect the vacuum advance. If there are two VR sensors, simply ignore the second one. While the Lean Burn system has a bad reputation, the distributors are just as reliable as the earlier ones, if not more so. One of the biggest sources of problems with the Lean Burn system appears to have been Chrysler’s decision to mount the computer on the air cleaner.
Many popular aftermarket distributors for classic Mopars also use VR sensors, including most of the choices from MSD and Accel. These directions will also apply to those distributors if you lock out the advance mechanism (if any).
Chrysler was not big on separate ignition modules and timing computers – when they brought out computer controlled timing, they went straight to integrating the ignition module into the timing computer. The Orange Box and electronic control units are not meant for computer controlled timing. Consequently, the easiest ways to control timing with Megasquirt are to either use a seven pin GM HEI module or, like Chrysler did, have the computer control the coil directly.
Using the MegaSquirt-I (MSnS-E) with Direct Coil ControlThis is a straightforward option with a V3.0 board. You’ll just need to add a BIP373 ignition control transistor. MegaSquirt-I PCBv3.0 Mods Required:
That’s it! External Ignition Wiring
MSnS-E Ignition Configuration
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Using the MegaSquirt-I (MSnS-E) with a 7 Pin HEI moduleIf you happen to have a V2.2 board, using a HEI module can be easier than building a VR conditioner input circuit on a board that never had one. This is also a viable option on a V3.0 board, although it does use a bit more hardware (and one more output wire) than the direct coil control option. The MSEXTRA forums have detailed information about how to set up Megasquirt to work with an HEI ignition. This write-up uses slightly different pins to better work with the relay board. MegaSquirt-I PCBv2.2 Mods Required:
MegaSquirt-I PCBv3.0 Mods Required:
External Ignition Wiring
MSnS-E Ignition Configuration
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Using the MegaSquirt-II PCBv3 with Direct Coil ControlThis requires a BIP373 ignition control transistor. If you’re assembling your MegaSquirt-II from a kit (Part# MS230-K):
If you’re modifying a DIYAutoTune.com MS230-C MegaSquirt-II Assembled ECU:Input Mod:
Output Mod:
That’s it– you’ve got your Megasquirt-II Engine Management System fully prepared to wire up to the Mopar distributor pickup, and drive the stock coil directly using the BIP373.
External Ignition Wiring:
TunerStudio Ignition Configuration:
You will need to set the dwell to match the particular coil you are using. More information on setting Trigger Offset:You must also set the initial position of the trigger (called the ‘trigger offset’), then check it using the Trigger Wizard in TunerStudio (Tools Menu). The trigger offset setting will vary according to your distributor position (where it is in rotation) but you’ll need to set it properly… Basically you use the Trigger Wizard and adjust the ‘trigger offset’ and/or twist your distributor until the advance number in the Trigger Wizard matches what you’re reading with your timing light. The +/- buttons on the trigger wizard will adjust your trigger offset. You’ll need to use these buttons and a timing light to make the number on your light, and the big number on the left in the Trigger Wizard, match up. Here’s the information on this: Before tuning your advance table, be sure to use a timing light to verify that your ‘trigger offset‘ is calibrated. Changing the Trigger Offset in TunerStudio will not change the displayed advance, instead, it changes the actual advance as seen with a timing light. Your goal is to make these two match. To do this, get your engine warmed-up (otherwise the timing moves as the temperature increases) and idling, then use a timing light to verify to be certain your actual advance as shown by a timing light equals your the advance display on the advance gauge in TunerStudio. (8, in this case). (Note that positive numbers denote BTDC, and negative numbers denote after TDC.) Image courtesy of Bowling and Grippo |
Using the MegaSquirt-II PCBv3 with a HEI ModuleIf you’re assembling your MegaSquirt-II from a kit (Part# MS230-K):
That’s it– you’ve got your Megasquirt-II Engine Management System fully prepared to work with a HEI ignition and stepper IAC.
If you’re using a DIYAutoTune.com MS2357-C MegaSquirt-II Assembled ECU:
External Ignition Wiring
TunerStudio Ignition Configuration:
Dwell willd epend on the coil; it is typically around 3.0 to 4.0 ms. Information On MegaSquirt EFI Conversions For Vintage Mopar Ignition EnginesMore information on setting Trigger Offset:You must also set the initial position of the trigger (called the ‘trigger offset’), then check it using the Trigger Wizard in TunerStudio (Tools Menu). The trigger offset setting will vary according to your distributor position (where it is in rotation) but you’ll need to set it properly… Basically you use the Trigger Wizard and adjust the ‘trigger offset’ and/or twist your distributor until the advance number in the Trigger Wizard matches what you’re reading with your timing light. The +/- buttons on the trigger wizard will adjust your trigger offset. You’ll need to use these buttons and a timing light to make the number on your light, and the big number on the left in the Trigger Wizard, match up. Here’s the information on this: Before tuning your advance table, be sure to use a timing light to verify that your ‘trigger offset‘ is calibrated. Changing the Trigger Offset in TunerStudio will not change the displayed advance, instead, it changes the actual advance as seen with a timing light. Your goal is to make these two match. To do this, get your engine warmed-up (otherwise the timing moves as the temperature increases) and idling, then use a timing light to verify to be certain your actual advance as shown by a timing light equals your the advance display on the advance gauge in TunerStudio. (8, in this case). (Note that positive numbers denote BTDC, and negative numbers denote after TDC.) |
Mopar ignition wire colors
Chrysler used several different color schemes on their distributor wires, and aftermarket distributors often use their own color schemes. Here is a list of sensors and their polarity.
| Distributor | Positive | Negative |
| Mopar with advance | Orange | Black |
| Lean Burn | Yellow or white | Blue or black |
| MSD distributor | Orange and black | Violet and black |
| MSD Flying Magnet crank trigger | Violet | Green |
A note on temperature sensors
Megasquirt can read the Mopar coolant temperature sensor if you calibrate it with EasyTherm (for MS-I) or the temperature sensor calibration tool (for MS-II). However, Megasquirt cannot share the stock temperature sensor with the stock temperature gauges. Chrysler used thermal temperature gauges well into the 1980s with a mechanical voltage regulator. This results in a lot of voltage noise at the sensor if it is connected to the original gauge. If you want to retain the existing temperature gauge, your best option is to install a second sending unit for Megasquirt.
