Injection Timing

All engines use a Sequential Fuel Injection (SFI) system. Injectors have a specific firing order and fuel injection is timed to piston movement. Spark plugs and injectors are fired in order:

• 1-3-4-2 on 2.5L.
• 1-5-3-6-2-4 on 4.0L.
• 1-8-4-3-6-5-7-2 on 4.7L.

In order for PCM to fire injectors in a specific order timed to crankshaft and piston movement, it has to establish a reference point. Establishing a reference point requires PCM inputs from the CKP sensor and CMP sensor. PCM will not allow engine to operate if CKP sensor signal is not received.

On 2.5L and 4.0L, CKP sensor is mounted on left upper side of transmission bellhousing. Sensor reads slots on outer edge of flywheel/flexplate. There are 2 groups of 4 slots on 2.5L, and 3 groups of 4 slots on 4.0L. On 4.7L, CKP sensor is mounted on right rear side of block, above starter. A tonewheel with notches on its outer edge is bolted to crankshaft. Each slot or notch causes a pulse to be generated as it passes under CKP sensor. CKP sensor provides PCM with crankshaft angle and speed. PCM converts crankshaft speed into engine RPM and crankshaft angle into piston position.