The 4HL1 firing order is 1-3-4-2. The ECM sequences injector pulses according to this order.
Battery + → Main Relay → Injector Common B+ Rail │ ┌─────────────────┼─────────────────┐ │ │ │ ┌───┴───┐ ┌───┴───┐ ┌───┴───┐ Inj #1 Inj #2 Inj #3 Inj #4 │ │ │ │ Yellow Blue Green Brown │ │ │ │ └───────┴────┬────┴───────┘ │ ECM Ground Drivers (Internal Low-Side Switches) 4hl1 injector wiring diagram
Remove the valve cover. Inspect the injector harness from the ECM pass-through connector down to each injector. Look for chafing, especially near cylinder #3 (common failure point). The 4HL1 firing order is 1-3-4-2
The serves as the map showing how the low-voltage signals travel from the sensors to the ECU, and how the high-voltage pulse width modulated (PWM) signals travel from the drivers to the injectors. Inspect the injector harness from the ECM pass-through
Red/White (Common/Power) and Blue/Yellow (Signal).
The 4HL1 injector harness runs under the valve cover in hot engine oil. Over time, vibration causes insulation to rub against the cylinder head or rocker arm bolts, creating intermittent shorts.
Unplug the ECM connector E (large 32-pin or similar) and all four injectors.