How to MegaSquirt your Gen III Hemi, using stock sensors and coilsUpdated 6/1/2018 – now with VVT settings! For MS3Pro settings, see section 5.3.4.16 of the MS3Pro manual for VVT motors, 5.4.7 for non-VVT motors.
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 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 wish to retain stock dash or body control module functions, we recommend letting the stock ECU run the throttle body and other functions, with the MS taking over just fuel and ignition. ECU ModificationsWe 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.
Ignition outputSince 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.
Other Things the ECU ControlsThe 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 – non VVTSet the following under Tach Input / Ignition Settings.
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 confirmed with a timing light. TunerStudio Configuration for MS3 – VVTSet the following under Tach Input / Ignition Settings. Spark mode: Toothed wheel 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. Alternative ignition modulesIf 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 recommend wiring it directly to the MS and using its falling edge ignition mode. A warning about spark tablesThe 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 partsECU options:
Other recommended parts
Hemi is a trademark of Chrysler and used to explain parts compatibility. Feedback welcomeIf you have any further information, contributions, or questions about this article, please contact us.
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