Why an MSD 6AL is different
Most factory ignitions are inductive. The coil stores energy in its magnetic field between sparks, and at high RPM there is less time to charge it fully, so spark energy can drop off right where you need it. The MSD 6AL is a capacitive discharge (CD) box instead. It charges an internal capacitor to roughly 460 to 480 volts, which takes about a millisecond, and dumps that into the coil when triggered. Spark energy stays strong right to the top of the rev range.
The 6 series also fires multiple sparks per event at lower RPM, all within about 20 degrees of crank rotation. As RPM climbs there is less time available, and above roughly 3,000 RPM it fires just one spark per event.
ECU settings
The MSD expects a points-style trigger signal. These settings make the Haltech provide one:
| Setting | Value | Why |
|---|---|---|
| Ignition Mode | Distributor | The MSD fires one coil through a distributor, so one output does all the work |
| Ignition Edge | Rising | Matches the signal edge the MSD responds to |
| Ignition Dwell Mode | Constant Duty 50% | The ECU is not charging a coil here, it is sending a square wave for the MSD to read |
Wiring
- Connect the MSD's white wire (the points trigger input) directly to Ignition Output 1 on the Haltech. That is true for every Haltech ECU, old or new.
- Do not connect any Haltech wire to the coil itself. The MSD drives the coil. With the MSD pushing several hundred volts into the coil, the coil primary is no place for an ECU wire.
- Wire the MSD's power, ground and coil connections as MSD specifies.
Checking ignition timing
At idle, those multiple sparks can make a timing light flicker or show a mark that seems to jump. Bring the engine above 3,000 RPM for the check, where the MSD is down to a single spark, and the light will read cleanly. Lock timing in the software while you do it, as covered in calibrating ignition timing, and see our guide to using a timing light.
Check that the white wire goes to Ignition Output 1, the dwell mode is Constant Duty 50%, and the edge is Rising. Those three account for most MSD start-up problems we see.
Running an MSD distributor for the trigger too? See our pages on the MSD cam sync distributor and MSD crank trigger kit.
