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.

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.

CKP sensor is located on transmission bellhousing, and provides PCM with crankshaft angle and speed. PCM converts crankshaft speed into engine RPM and crankshaft angle into piston position.

On 2.5L engine, slotted flywheel/flexplate, rotating past CKP sensor, contains 2 groups of 4 slots located 180 degrees apart. Each group of slots represents position of 2 pistons. Pistons No. 1 and 4 approach TDC at same time and use same flywheel slot, while piston No. 3 is matched with piston No. 2.