Injection Timing

WARNING: This page is about a different car, the 2003 Jeep Grand Cherokee. However, it is still accessible from the selected car via links, so may be relevant.

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:

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

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.