Engine Controls - Theory & Operation - Cng, Flex-Fuel & Gasoline: Overview Ford Explorer III

Hardware Limited Operation Strategy

HLOS is a system of alternate circuitry that provides minimal engine operation if the PCM or EEPROM fails. During HLOS, all self-test function will stop and system will be controlled by electronic hardware.

HLOS Allowable Output Functions

1. Spark Output Controlled Directly By CKP Signal
2. Fixed Fuel Pulse Width Synchronized With CKP Signal
3. Fuel Pump Relay Energized
4. Idle Speed Control Output Signal Functional

HLOS Disabled Outputs To Default State

1. EGR Solenoids
2. No Torque Converter Clutch Lock-Up

Description

Integrated Electronic Ignition (EI) system consists of a Crankshaft Position (CKP) sensor, coil pack(s), wiring and PCM. Coil On Plug (COP) integrated EI system uses a separate coil for each spark plug and each coil is mounted directly onto spark plug. COP integrated EI system eliminates need for spark plug wires but does require input from Camshaft Position (CMP) sensor. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 9)

1. The CKP sensor is used to indicate crankshaft position and speed by sensing a missing tooth on a pulse wheel mounted to crankshaft. The CMP sensor is used by COP Integrated EI System to identify top dead center of compression of cylinder No. 1 to synchronize firing of individual coils. For additional CKP or CMP sensor information, see «CAMSHAFT POSITION SENSOR»(ref-153170-S37687056772003032100000) or «CRANKSHAFT POSITION SENSOR»(ref-153170-S09938082842003032100000) under INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.
2. The PCM uses CKP signal to calculate a spark target and then fires coil pack(s) to that target shown. (Scheme 10) The PCM uses CMP sensor on COP Integrated EI Systems to identify top dead center of compression of cylinder No. 1 to synchronize firing of individual coils.
3. The coils and coil packs receive their signal from PCM to fire at a calculated spark target. Each coil within pack fires 2 spark plugs at the same time. The plugs are paired so that as one fires during compression stroke, the other fires during exhaust stroke. The next time the coil is fired, the situation is reversed. The COP system fires only one spark plug per coil and only on compression stroke. PCM acts as an electronic switch to ground in the coil primary circuit. When the switch is closed, battery positive voltage (B+) applied to coil primary circuit builds a magnetic field around primary coil. When the switch opens, power is interrupted and primary field collapses inducing high voltage in secondary coil windings and the spark plug is fired. A kickback voltage spike occurs when primary field collapses and the PCM uses this voltage spike to generate an Ignition Diagnostic Monitor (IDM) signal. IDM communicates information by pulse width modulation in PCM.
4. The PCM processes CKP signal and uses it to drive tachometer as Clean Tach Output (CTO) signal.

Scheme 9

Scheme 10

There are four possible types of Variable Cam Timing (VCT) systems. The 2003 ZX2 are Exhaust Phase Shifting (EPS) system. The exhaust cam is the active cam and is being retarded. The 2003 LS, Thunderbird and Focus SVT vehicles have Intake Phase Shifting (IPS) system. A intake phase shifting system will move the intake cam in the advance direction. The other two possible systems are Dual Equal Phase Shifting (DEPS) both intake and exhaust cams are phase shifted equally as well as Dual Independent Phase Shifting (DIPS) where the cams are shifted independently. The systems have three operational modes; idle, part throttle, wide open throttle and a default mode. At idle and (low engine speeds with closed throttle) the phase angle is controlled by air flow and engine coolant temperature. At part and wide open throttle the PCM controls cam timing based on engine RPM, load, and throttle position. VCT systems provide reduced emissions and enhance engine power, fuel economy and idle quality. IPS systems have the added benefit of improve torque. In addition a VCT system will eliminate the need for an external Exhaust Gas Recirculation (EGR) system. The elimination of EGR system is accomplished by controlling the overlap in valve opening between the intake valve opening and exhaust valve closing. Increased vehicle reliability is achieved with the elimination of the EGR system.

The VCT system consists of an electric hydraulic positioning control solenoid, a CMP and trigger wheel. The CMP trigger wheel has a number of equally spaced teeth equal to the number (n) of cylinders on a bank plus one extra tooth (n+1). Four cylinder and V8 engines use a CMP 4+1 tooth trigger wheel. V6 engines use a CMP 3+1 tooth trigger wheel. The extra tooth placed between the equally spaced teeth represents the CMP signal for that bank. A CKP provides the PCM with crankshaft positioning information in 10 degree increments.

The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 11)

1. The PCM receives input signals from the IAT, ECT, CMP, TP, MAF and CKP to determine the operating conditions of the engine. At idle (low engine speeds and closed throttle) the PCM controls camshaft position based on air and coolant temperatures. During part and wide open throttle, camshaft position is determined by engine RPM, load and throttle position. The VCT system will not operate until the engine is at normal operating temperature.
2. VCT system is enabled by PCM when the proper conditions are met. PCM disables VCT system if a fault is detected.
3. The CKP signal is used as a reference for CMP positioning.
4. The PCM calculates and determines the desired camshaft position. It will continually update the VCT solenoid duty cycle until desired positioning is achieved. A difference between the desired and actual camshaft position represents a position error in the PCM's VCT control loop. The PCM will disable the VCT and place the camshaft in a default position if a fault is detected.
5. Oil flows to either side of the piston chamber in the VCT assembly, which changes the linear piston motion to a rotational motion that advances or retards the camshaft.

Scheme 11

The Secondary Air Injection (AIR) system controls emissions during first 20-120 seconds of engine operation by forcing air downstream into exhaust manifolds to oxidize hydrocarbons and carbon monoxide created by running rich at start up.

Exhaust Gas Recirculation (EGR) system controls oxides of nitrogen (NOx) emissions. Small amounts of exhaust gases are recirculated back into combustion chamber to be reburned with air/fuel charge. There are 2 different types of EGR systems that may be used

1. «DIFFERENTIAL PRESSURE FEEDBACK EGR SYSTEM»(ref-153170-S34615645432003032100000)
2. «ELECTRIC MOTOR EGR SYSTEM»(ref-153170-S25753592652003032100000)

Torque based Electronic Throttle Control (ETC) is a strategy that delivers a transmission output shaft torque (via throttle angle) based on driver demand (pedal position). It utilizes the Visteon Gen II electronic throttle body (replaces throttle cable). see scheme 84 Torque based ETC strategy was developed mainly to improve fuel economy. This is possible by not coupling the throttle angle to pedal position, which enables various fuel economy schemes and technologies.

Torque based ETC enables aggressive automatic transmission shift schedules (earlier upshifts and later downshifts). This is possible by adjusting the throttle angle to achieve the same wheel torque during shifts. In other words, the engine shifts can result is an engine lugging condition (low RPM and low manifold vacuum) while still delivering the same torque requested by the driver. It should be noted that the ETC system includes a wrench light on the instrument cluster that illuminates when a fault is detected. Faults are also accompanied by DTCS and the "Check Engine Soon" light.

It also enables many fuel economy/emission improvement technologies such as

1. VCT (deliver same torque during transitions)
2. Continuously Varying Transmission (CVT)
3. Hybrid Electric Vehicle (HEV)

Torque based ECT also results is a less intrusive vehicle and engine speed limiting, along with smoother traction control. Other generic benefits of ETC are

1. Eliminate cruise control actuators
2. Eliminate ISC Bypass actuator
3. Better airflow range
4. Packaging (no cable)

PCM controlled charging system provides many additional benefits over integral generator regulator system. First benefit is improved battery life. In an integral generator regulator system, regulator set point is established by a temperature sensor in the regulator which estimates battery temperature. With PCM controlled generator, regulator voltage set points are determined by PCM and communicated to regulator via generator communication line. PCM uses a calibratable algorithm to estimate battery temperature. Improving battery temperature will reduce battery damage caused by over and undercharging.

Second benefit is improved engine performance. Whenever PCM senses a Wide Open Throttle (WOT), PCM will momentarily lower regulator voltage set point. This reduces torque load of the generator on engine and improves acceleration. PCM has a calibratable time limit on this reduced voltage feature. This prevents the generator output from being cut back for an extended WOT period, which could cause battery discharge.

Third benefit is improved idle stability. In response to PCM generator communication signal, regulator uses a generator monitor signal to provide feedback to PCM. Generator monitor signal provides PCM with charging system information. If the charging system receives a transient electrical load which would normally affect idle stability, the PCM is notified. Because PCM can anticipate additional loads, actions can be taken to minimize idle sag. PCM can choose to either reduce regulator set point or increase engine idle speed.

Fourth benefit is reduced cranking efforts. PCM can reduce mechanical load on starter by initially commanding a low voltage set point. This may improve start times.

If PCM detects a charging system error, charge indicator will illuminate. Charge indicator will illuminate if PCM fails to see a signal on generator monitor line for a time period greater than 500 milliseconds. This command will also be used to indicate over-voltage conditions detected by generator.

Each time ignition switch is turned to RUN position, cluster will perform a bulb check by illuminating charge indicator. PCM will send a low voltage command if charging system is functioning properly. This message should be sent 250-450 milliseconds after ignition switch is turned to RUN position. If a low voltage command is not received by cluster, cluster will continue to illuminate charge indicator indefinitely.

See also:
• KEEP ALIVE RANDOM ACCESS MEMORY RESET PROCEDURE