How to MegaSquirt Your Chrysler Hemi Engine

Using stock sensors and coils

Application(s): This article covers the new Mopar Hemi Magnum engines (5.7, 6.1, or 6.4) that Chrysler started producing in 2002, as used in the Dodge Ram and Durango, 300C, Magnum, and Challenger.

Level of control:  Fuel and ignition control. This article does not cover the drive by wire setup, MDS (cylinder deactivation) or the “cam in cam” variable valve timing that appeared in 2009, or the host of systems tied into the stock ECU’s network. If you’re swapping a motor into an older car, you can just put a cable operated throttle body on there and go. If you’re using the MegaSquirt on a factory Hemi car – and not building a gutted race car – we recommend letting the stock ECU run the throttle body and other functions, with the MS taking over just fuel and ignition.

ECU Modifications

We recommend the MS3 for these motors, in order to get sequential fuel control and sequential spark control. Plus, the MS3 has native support for the OEM cam and crank sensors.

Using the MS-III PCB V3.0 or V3.57 ECUAnd the MS3X expansion board

  • Set up the ECU up to trigger from the VR Input. Jumper TachSelect to VRIN and TSEL to VROUT for a V3.0. For a V3.57, set the JP1 jumper on the main board to the 1-2 position, and set J1 to the 3-4 position.
  • We’ll need a 5 volt pull up on the crank sensor. There are two ways to do this – internal or external.
    • Internal pull up: For a V3.57, solder a 1K resistor in the R57 position. For a V3.0, solder a 1K resistor to a length of wire and run it from the 5 volt point in the proto area to the TachSelect-VRIN jumper.
    • External pull up: Connect a 1K resistor between the wire on pins 24 and 26 on the main board harness.
  • Use the MS3X pull up jumper for the cam sensor pull up (JP7).
  • For starting trim pot settings, we recommend having R56 (main board hysteresis) and R32 (MS3X hysteresis) fully counterclockwise. V3.0 pots will click when they reach the end of their travel; for a V3.57 or the MS3X board, just give them six full turns counterclockwise to move them to the end. Start with R52 (main board threshold) one full turn clockwise after setting it fully counterclockwise for a V3.57, or three turns clockwise for a V3.0. For R11 (MS3X zero crossing), start with one turn clockwise from the fully counterclockwise slot.

That’s it!

Ignition output

Since the factory coils do not have built in ignition modules, we recommend using a pair of QuadSpark ignition modules to fire the coils. There are two coil versions used on Hemi motors. If you have the coils with two boots underneath them, set the number of coils to “coil on plug.” If you have the coils with one boot underneath them and the other connector connecting to a spark plug wire on the companion cylinder, set the number of coils to “wasted COP.” In either case, the wiring is the same.

  • Spark A – cylinder 1
  • Spark B – cylinder 8
  • Spark C – cylinder 4
  • Spark D – cylinder 3
  • Spark E – cylinder 6
  • Spark F – cylinder 5
  • Spark G – cylinder 7
  • Spark H – cylinder 2

Other Things the ECU Controls

The stock ECU ties into the gauges and many other functions on the cars and trucks that used these motors stock. If you are installing a MegaSquirt on these cars and want these functions to work like stock, see our guide to MegaSquirt parallel installations for some tips on how to keep the stock ECU functional.

If you’re swapping a new Hemi into something from the muscle car era, this will not be a major concern. You will want to have the MegaSquirt control the fuel pump relay, and it can also run a tachometer off its tach output pin since you no longer have a distributor to trigger the stock tach.  The MegaSquirt tach output works with most aftermarket tachometers. If it does not work with your stock tach, you may need a tach adapter such as the ones used on aftermarket CDI ignitions.

One easy way to get around the drive by wire for engine swaps: BBK has recently come out with bolt on cable operated throttle bodies for these motors.

TunerStudio Configuration for MS3

Set the following under Tach Input / Ignition Settings.

  • Spark mode: 36-2+2
  • Use cam signal: Yes
  • Cam input: MS3X cam in
  • Ignition Input Capture: Rising Edge
  • Spark Output:  Going High / Inverted for QuadSpark ignition modules.  It is critical to get the Spark Output Inverted setting correct, as setting this wrong can result in damage to the ignition module or coil.
  • Number of coils: Coil on plug or wasted COP (see above)
  • Spark A output pin: MS3X spark

How To MegaSquirt Your Chrysler Hemi Engine

Dwell settings will depend on the coil used; 2.0 msec is a safe starting point.  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.

The trigger angle is hard-coded with this setting and should be left at zero.

Note that if you are using some other sort of ignition module (such as certain distributorless capacitive discharge setups), it is possible the spark output setting  may need to be set to Going Low / Normal. Most ignition modules we are aware of that could be used on these motors should use Going High / Inverted, including the QuadSpark, Bosch 211, AEM distributorless ignition module, and M&W Pro 18. If you are using an M&W Pro 18, we recomemnd wiring it directly to the MS and using its falling edge ignition mode.

A warning about spark tables

The new Hemis neither need nor appreciate a lot of timing advance. We’ve found that 22 degrees at full throttle is all the advance one is likely to need on race gas, and can be too much on pump gas.  The default MS3 timing table is for an older combustion chamber with a much lower flame front speed, and needs to be backed off before you start tuning. I’d start with no more than 18 to 20 degrees at full throttle (100 kPa).  I’ve heard Mopar faithful comment “This engine isn’t a real Hemi” – and they should not be tuned with the huge amounts of spark advance a classic 426 would have required. The newer head has a much faster burn rate and is considerably more efficient.

Suggested parts

ECU options:

Other recommended parts


Hemi is a trademark of Chrysler and used to explain parts compatibility.

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