This report applies to the common heat-sink-style GM Gen-3 4.8/5.3/6.0 truck smart coil commonly identified as:
ACDelco D585
GM 10457730
Delphi GN10119
Wells C1251
Standard Motor Products UF262
Physical appearance alone is not sufficient because LS coil families use different housings and some online pinouts mix coil types. Verify the molded cavity letters and preferably the part number on the actual coil before wiring.
Four-pin connector pinout
Viewed by the molded cavity letters, not by an assumed left-to-right photo orientation:
Mating connector identifiers reported by MegaManual are GM 12580353 / Delphi 15439568. Connector suppliers may sell these under application descriptions rather than those bare numbers.
Research confirms the D585 pinout: A power ground, B signal ground, C trigger, D switched 12 V. It charges with a >4 V high signal and sparks on the falling edge; start around 3.5 ms dwell at 14 V.
Important finding: firing both coils at every trigger would approach 93% dwell duty at 8000 RPM, so the controller needs alternating cylinder outputs rather than permanently tied triggers. Full details: D585 Coil Research.
I’ll evaluate strategies that work with two potentially identical pickup events—startup wasted spark, trial-and-confirm phasing, crank-acceleration detection, target asymmetry, and adding an index sensor—then rank them by safety and implementation risk.
Startup and Phase IdentificationProblem definition
The Rotax 593 has one VR pickup and appears to produce two crank-reference events per revolution, about 180° apart. If those events are electrically and geometrically identical, the controller knows that one cylinder is approaching its firing position but cannot initially know whether that event belongs to the MAG or PTO cylinder.
This is not a four-stroke cam-phase problem: each two-stroke cylinder fires once per crank revolution. It is a cylinder-label problem caused by two symmetric crank events and two separate single-output coils.
If the targets are truly identical, no passive algorithm can identify MAG versus PTO from the first pulse alone. Additional information must come from target asymmetry, another sensor, store...
This report applies to the common heat-sink-style GM Gen-3 4.8/5.3/6.0 truck smart coil commonly identified as:
ACDelco D585
GM 10457730
Delphi GN10119
Wells C1251
Standard Motor Products UF262
Physical appearance alone is not sufficient because LS coil families use different housings and some online pinouts mix coil types. Verify the molded cavity letters and preferably the part number on the actual coil before wiring.
Four-pin connector pinout
Viewed by the molded cavity letters, not by an assumed left-to-right photo orientation:
Table
Cavity
Function
Common OEM wire color
Required connection
A
Coil primary / power ground
Black
Short, heavy wire to engine block or cylinder-head ground
B
Ignition low-noise / signal ground
Brown
Controller signal-ground reference
C
Logic spark-control input
Varies
Protected ignition-output signal from controller
D
Switched battery supply
Pink
Fused, switched nominal 12 V supply
Mating connector identifiers reported by MegaManual are GM 12580353 / Delphi 15439568. Connector suppliers may sell these under application descriptions rather than those bare numbers.
Trigger voltage and polarity
The D585 contains its own high-current igniter. The controller supplies a low-current logic signal rather than switching primary current directly.
Input high: approximately 3–5 V or higher within the normal logic-driving arrangement.
EFI Hardware specifies greater than 4 V to begin charging.
Input low: EFI Hardware specifies less than 1 V.
The coil charges while cavity C is high.
The coil fires when cavity C transitions from high to low.
In ECU terminology this is active-high dwell with a falling-edge spark. MegaSquirt calls the setting “Going High.”
A 5 V push-pull buffer is the safest design target. A bare 3.3 V MCU output is not accepted as guaranteed because the most explicit wiring source specifies >4 V for charge. Use a protected 5 V logic driver/buffer, default-low pull-down, series resistor, and transient/ESD protection. The output must remain low during reset, boot, brownout, and programming.
Dwell
Sources differ slightly because D585 behavior varies with supply voltage and test method:
MegaSquirt hardware guide recommendation: 3.5 ms.
EFI Hardware recommendation: 3.5 ms at 14.4 V.
MegaManual historical upper recommendation: 4.5 ms maximum.
JFE Tech recommendation: approximately 5.0 ms, with no useful additional output beyond that point.
For this project, start with 3.5 ms near 14 V, then characterize coil current and spark stability. Do not begin with 4.5–5.0 ms.
The D585 family is reported to include current/over-dwell protection, with an automatic limit or auto-discharge around 8 ms. This is not a normal operating mode. Excessive dwell can create an unintended early spark, so firmware must hard-limit dwell and force the trigger low on faults.
Preliminary battery-voltage compensation
A precise D585 OEM dwell-compensation table was not found in an authoritative GM/Delphi public datasheet. JFE Tech reproduces a community-derived table spanning 8–16 V, but it should not be treated as a production calibration without bench verification.
Recommended development approach:
Use 3.5 ms near 13.5–14.4 V.
Measure primary supply current with a current clamp or low-inductance shunt.
Increase dwell at lower voltage only enough to reach the same peak current/energy.
Cap commanded dwell below the auto-discharge region under every voltage and timing condition.
Reduce dwell if coil temperature rises excessively at sustained engine speed.
Power supply and grounding
Nominal supply: switched automotive 12 V; available application data and compensation tables cover approximately 8–16 V.
The snowmobile power system must be rectified and regulated before feeding the coils and controller. Do not connect D585 coils directly to an unregulated lighting/magneto winding.
Cavity A carries noisy, high-current primary return and must go to the engine with short, heavy wiring.
Cavity B is the clean logic reference and should return to controller signal ground. Join signal ground and engine/power ground at a controlled point rather than sharing a long high-current coil-ground path.
Add local supply decoupling close to the coil pair. MegaManual suggests 1 µF on the 12 V supply, but that is high-frequency suppression—not adequate bulk energy storage by itself. The final harness should include automotive-rated bulk capacitance plus smaller ceramic/film suppression selected after measuring the actual supply ripple and wiring inductance.
Use load-dump, reverse-polarity, overvoltage, and conducted-transient protection on the controller/coil supply.
No reliable public D585 primary-current maximum was found in the reviewed sources. Therefore fuse, wiring, regulator, and stator sizing must not be based on an assumed current figure. Bench-measure actual current using the exact coils and dwell schedule before finalizing the power system.
Critical two-stroke duty-cycle issue
The D585 was designed for individual cylinders in a four-stroke engine, where each coil normally fires once every two crank revolutions. This Rotax 593 two-stroke requires each cylinder to fire once every crank revolution.
At 8000 RPM:
One firing per revolution per coil = 133.3 sparks/s per coil.
A 3.5 ms dwell gives approximately 46.7% commanded charge duty per coil.
If both coils are fired at both 180-degree trigger events, each coil receives 266.7 sparks/s.
At 3.5 ms dwell, that becomes approximately 93.3% commanded charge duty, leaving only 0.25 ms between commands.
Therefore the previously considered method of driving both LS coils together at every trigger is not acceptable as the default architecture. It risks severe coil heating, supply overload, current limiting, and unintended auto-discharge at high RPM.
The controller should identify or establish the alternating trigger phase and fire only the appropriate cylinder’s coil at each 180-degree event. If the two crank targets are indistinguishable, safe phase acquisition needs an additional index/reference, a measurable asymmetry in the pickup pattern, or a controlled startup strategy that stops simultaneous firing once phase is known. Pickup oscilloscope data is required before final architecture selection.
Even with one firing per revolution, the D585 operates at twice the firing frequency of the same-RPM four-stroke application. Sustained-temperature and current testing is mandatory.
Recommended controller interface
Per coil:
5 V automotive-qualified push-pull logic buffer or ignition-output driver.
Trigger idle state low.
Hardware pull-down so the coil cannot charge while the MCU is unpowered or resetting.
Series output resistor for edge-current/transient limiting.
Independent output for each coil; do not permanently tie C inputs together.
Firmware maximum-dwell watchdog independent of the normal timing scheduler.
Immediate trigger-low shutdown for missing pickup, overspeed, brownout, watchdog reset, or invalid timing state.
Strong application source for cavity functions, >4 V high, <1 V low, falling-edge spark, and 3.5 ms at 14.4 V. The document is labeled LS1-style, so actual D585 cavity letters must still be verified on the physical coil.
Vendor/technical secondary source for logic behavior and voltage-compensation examples; use calibration values cautiously.
Required confirmation before schematic capture
Provide a clear photo of the coil label and connector face showing cavity letters A–D. The actual part number determines whether this D585 research applies without modification.