Jeep Engines - Oljeep

4.7L POWER TECH V-8 361Fuel Tank Filler Tube CapThe plastic fuel fill cap is threaded onto the end of the fuelfill tube.The loss of any fuel or vapor out of fuel filler tube isprevented by the use of a pressure-vacuum fuel fill cap.Relief valves inside the cap will release fuel tank pressureat predetermined pressures. Fuel tank vacuum will also bereleased at predetermined values. This cap must be replacedby a similar unit if replacement is necessary. This is in orderfor the system to remain effective.Caution: Remove fill cap before servicing any fuel systemcomponent. This is done to help relieve tank pressure. Ifequipped with a California emissions package and a LeakDetection Pump (LDP), the secondary seal below the fillcap must be pressed (opened) to relieve fuel tank pressure.POWERTRAIN CONTROL MODULE (PCM)The Powertrain Control Module (PCM), formerly referredto as the SBEC or engine controller, is a pre-programmed,triple microprocessor digital computer. It regulates ignitiontiming, air-fuel ratio, emission control devices, chargingsystem, certain transmission features, speed control, airconditioning compressor clutch engagement and idle speed.The PCM can adapt its programming to meet changingoperating conditions.The PCM receives input signals from various switches andsensors. Based on these inputs, the PCM regulates variousengine and vehicle operations through different systemcomponents. These components are referred to as PCMOutputs. The sensors and switches that provide inputs to thePCM are considered PCM Inputs.The PCM adjusts ignition timing based upon inputs itreceives from sensors that react to engine rpm, manifoldabsolute pressure, engine coolant temperature, throttleposition, transmission gear selection (automatictransmission), vehicle speed, and the brake switch.The PCM adjusts idle speed based on inputs it receivesfrom sensors that react to throttle position, vehicle speed,transmission gear selection, engine coolant temperature, airconditioning clutch switch, and brake switch.Based on inputs that it receives, the PCM adjusts ignitioncoil dwell. The PCM also adjusts the generator charge ratethrough control of the generator field and provides speedcontrol operation.Modes of OperationAs input signals to the PCM change, the PCM adjusts itsresponse to the output devices. For example, the PCM mustcalculate different injector pulse width and ignition timingfor idle than it does for wide open throttle.The PCM operates in two different modes: Open Loop andClosed Loop.During Open Loop modes, the PCM receives input signalsand responds only according to preset PCM programming.Input from the oxygen (0,) sensors is not monitored duringOpen Loop modes.During Closed Loop modes, the PCM will monitor theoxygen (0,) sensors input. This input indicates to the PCMwhether or not the calculated injector pulse width results inthe ideal air-fuel ratio. This ratio is 14.7 parts air-to-I partfuel. By monitoring the exhaust oxygen content through the0, sensor, the PCM can fine tune the injector pulse width.This is done to achieve optimum fuel economy combinedwith low emission engine performance.The fuel injection system has the following modes ofoperation:Ignition switch ONEngine start-up (crank)Engine warm-upIdleCruiseAccelerationDecelerationWide open throttleIgnition switch OFFThe ignition switch On, engine start-up (crank), engine warmup,acceleration, deceleration, and wide open throttle modesare Open Loop modes. The idle and cruise modes (with theengine at operating temperature) are Closed Loop modes.