See Figure 1
All 1991-98 Jeep vehicles employ a sequential Multi-Point Fuel Injection (MPI) System. The system, similar in construction to the Renix multi-point fuel injection system, is controlled by a Powertrain Control Module, or PCM. The PCM is a pre-programmed, dual microprocessor digital computer. It regulates ignition timing, air-fuel ratio, emission control devices, charging system, speed control and idle speed.
Fuel is injected into the intake port directly above the intake valve in precise metered amounts through electrically operated injectors. The injectors are fired in a specific sequence by the PCM. The PCM maintains an air/fuel ratio of 14.7/1 by constantly adjusting injector pulse width. Injector pulse width is the length of time the injector is open.
The PCM adjusts ignition timing by controlling the ignition coil. Base ignition timing is not adjustable.
Removal & Installation
- Disconnect the negative battery cable.
- Remove the coolant reserve tank and disengage the three electrical connectors from the PCM.
- Remove the three PCM mounting bolts and carefully remove the PCM.
- Installation is the reverse of removal.