What it is and why you'd use it
The MSD 85141 (now under Holley) drops into a distributor housing and carries an adjustable hall effect sensor. Paired with a crank trigger, it gives the ECU a once-per-cycle home (sync) signal, which tells it which cylinder is coming up. That's what lets a Haltech run sequential injection and direct-fire coils instead of batch fire and a distributor. The sensor's position is adjustable, so you can set the sync signal to arrive with the right lead for your ECU. Haltech doesn't sell this part, so you'll get it from MSD or Holley.
Elite settings
| Home input setting | Use |
|---|---|
| Pullup | Enabled |
| Sensor Type | Hall Effect |
| Filter Level | 0 |
| Edge | Falling |
Wiring to the home 4-core
| Function | Haltech home cable color | MSD sensor wire |
|---|---|---|
| Sensor supply, 12 V | Red | Red |
| Sync signal (Home +) | Yellow | Green |
| Signal ground | Blue | Black |
Keep the trigger wiring in its shielded cable and away from coil and ignition leads, which are the usual cause of sync errors.
Powering it from 5 V
MSD says the output swings to about 1.5 V below whatever supply voltage you feed the sensor. On 12 V that leaves plenty of signal, but on a 5 V supply the high level is lower, so the default thresholds may not read it cleanly. In that case, use custom home settings with the Arming Voltage Threshold at 3.0V and the Activation Voltage Threshold at 1.0V.
Checking it works
Crank the engine with the trigger scope running and confirm a clean, consistent home pulse in a sensible place relative to the crank teeth. Then check base timing with a light, as described in setting your TDC offset angle. If the pulse sits near a crank tooth edge, rotate the sensor to move it clear.
More reading: engine trigger systems explained, finding hall effect sensor pinouts, and the matching MSD crank trigger kit.
