Faults

Dead ECU / no USB

• L4 has key-on 12 V to ECU ground.
• M3 and L3 are on a real engine earth.
• E4 is grounding the relay coil; M4 then shows 12 V.
• USB: J2 white, J1 green, shielded cable, ST VCP driver installed.

No RPM while cranking

• VR: A4 / A3, twisted, swap polarity once.
• Hall: A4 only, A3 open, sensor actually powered.
• Trigger type and tooth count match the wheel.
• Look at the composite logger in the Core EFI console before you touch fueling.

RPM yes, no fuel

• 4-cyl: C4, C3, B4, B3 actually clicking on the output test.
• 6-cyl: K1, J3, J4 toggling into the 3-channel injector driver, and that box has 12 V.
• 8-cyl: J4 / J3 toggling into the external driver, and that box has 12 V.
• Injector +12 V from main-relay 87.
• Fuel-pump relay on D2 clicks.

No spark

• 4-cyl / 8-cyl wasted spark: smart coil or igniter on K4–K1.
• 6-cyl: smart coils on K4, K3, K2. K1 is the injector driver, not a coil.
• Coil +12 V present while cranking (relay 87).
• Fixed-timing test at 10° with a light on cylinder 1.

Sync loss under load

• Shield the crank pair. Cross it away from injector and coil looms.
• Power ground on the block, not a painted chassis hole.
• VR gap too large, or a cracked reluctor.