Engine Controls - Theory & Operation - Gasoline & Ngv: Overview Ford Excursion I

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

Catalyst Efficiency Monitor Description

Catalyst Efficiency Monitor uses an oxygen sensor before and after catalyst to infer hydrocarbon efficiency based on oxygen storage capacity of catalyst. Under normal, closed-loop fuel conditions, high efficiency catalysts have significant oxygen storage. This makes switching frequency of rear Heated Oxygen Sensor (HO2S) very slow and reduces amplitude of those switches as compared to switching frequency and amplitude of front HO2S. As catalyst efficiency deteriorates due to thermal and/or chemical deterioration, its ability to store oxygen declines. Post-catalyst or downstream HO2S signal begins to switch more rapidly with increasing amplitude, approaching switching frequency and amplitude of pre-catalyst or upstream HO2S.

Note. The predominant failure mode for high mileage catalysts is chemical deterioration (phosphorus deposition on front brick of catalyst), not thermal deterioration.

All vehicles utilize a Federal Test Procedure (FTP) based catalyst monitor. Meaning catalyst monitor must run during a standard FTP emission test. This differs from a 20 second steady state catalyst monitor used in 1994-96 vehicles. Currently, 2 slightly different versions of catalyst monitor are utilized; Switch Ratio Method and Index Ratio Method. Beginning with 2001 model year, both versions will continue to be used. See CATALYST EFFICIENCY MONITOR - SWITCH RATIO METHOD (1996-2002) or CATALYST EFFICIENCY MONITOR - INDEX RATIO METHOD (SOME 2001-LATER) .

General Catalyst Monitor Operation

Monitor execution is once per drive cycle. In order for catalyst monitor to run, HO2S monitor must be complete and Secondary AIR and EVAP system functional with no stored DTCs. If catalyst monitor does not complete during a particular driving cycle, the already accumulated switch/signal data is retained in Keep Alive Memory (KAM) and is used during next driving cycle to allow catalyst monitor a better opportunity to complete. Rear HOS2 sensors can be located in various configurations to monitor different kinds of exhaust systems. In-line engines and many V-engines are monitored by their individual bank. A rear HO2S sensor is used along with the front fuel control HO2S sensor for each bank. These 2 sensors are used on an in-line engine; 4 sensors are used on a V-engine. Some V-engines have exhaust banks that combine into a single underbody catalyst. These systems are referred to as Y-pipe systems. They use only one rear HO2S sensor along with 2 front, fuel-control HO2S sensors. Y-pipe system uses 3 sensors in all. For "Y" piped systems, 2 front HO2S sensor signals are combined by PCM software to infer what HO2S signal would have been in front of monitored catalyst. Inferred front HO2S signal and the actual single rear HO2S signal is then used to calculate switch ratio.

Most vehicles that are part of Low Emission Vehicle (LEV) catalyst monitor phase-in will monitor less than 100 percent of catalyst volume. Often this is the first catalyst brick of catalyst system. Partial volume monitoring is done on LEV and Ultra Low Emission Vehicle (ULEV) vehicles in order to meet the 1.75 grams per mile emission standard for smog causing carbon monoxide (CO). Many applications that utilize partial-volume monitoring place rear HO2S sensor after first light-off catalyst can or, after second catalyst can in a 3-can per bank system. A few applications place HO2S in middle of catalyst can, between first and second bricks. Index ratios for Ethanol (Flex-fuel) vehicle vary based on the changing concentration of alcohol in fuel. The malfunction threshold typically increases as percentage of alcohol increases. For example, a malfunction threshold of 0.5 may be used at E10 (10 percent ethanol) and 0.9 may be used at E85 (85 percent ethanol). Malfunction thresholds are therefore adjusted based on percentage of alcohol in fuel.

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 1)

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-136232-S20632679742002022600000) or «CRANKSHAFT POSITION SENSOR»(ref-136232-S02400579752002022600000) 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 2) 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 1

Scheme 2

Variable Cam Timing (VCT) system allows exhaust cam to advance and retard at varying engine speeds. This is to reduce exhaust emissions and increase fuel economy. As exhaust cam retards in relation to crankshaft position, residual exhaust gases are left in combustion chamber. Residual gases cool combustion chamber and are inert when mixed with incoming fresh charge of fuel and air. This results in better fuel economy and lower Nitrogen Oxides (NOx) and Hydrocarbons (HC) emitted from the engine. VCT system eliminates the need for an Exhaust Gas Recirculation (EGR) system.

VCT system applies only to Escort and Focus 2.0L ZETEC (VIN 3) engines. VCT system consists of control solenoid, 5-tooth pulse ring (4+1) on exhaust camshaft, Intake Air Temperature (IAT) sensor, Engine Coolant Temperature (ECT) sensor, Camshaft Position (CMP) sensor, Mass Air Flow (MAF) sensor, Crankshaft Position (CKP) sensor and PCM. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 3)

1. PCM receives input signals from IAT sensor, ECT sensor, CMP sensor, MAF sensor and CKP sensor for determining operating conditions of the engine.
2. VCT system is enabled by PCM when the proper conditions are met. PCM disables VCT system if a fault is detected.
3. PCM calculates relative cam position using CMP sensor and data from (4+1) pulse ring mounted on exhaust camshaft. Relative cam position is calculated by measuring time between the rising edge of Profile Ignition Pickup (PIP) and the falling edge of VCT pulse.
4. PCM continually calculates a cam position error value based on the difference between desired and actual position and a duty cycle is commanded for VCT solenoid valve. Engine oil is allowed to flow to VCT unit. For additional VCT solenoid valve information, see «VARIABLE CAM TIMING SOLENOID VALVE»(ref-136232-S41433042262002022600000) .
5. Oil flows to either side of the piston chamber changing a linear motion from piston to a rotation motion from the helical mechanism in VCT unit. During closed loop, PCM outputs a revised duty cycle to VCT solenoid valve to correct for cam position error. For additional VCT unit information, see «VARIABLE CAM TIMING UNIT ASSEMBLY»(ref-136232-S14367642992002022600000) .

Scheme 3

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-136232-S14002831562002022600000)
2. «ELECTRIC MOTOR EGR SYSTEM»(ref-136232-S20834590972002022600000)

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.