Motor 4.3L (Blazer 98) - Teoria y Funcionamiento

1998 Chevrolet Blazer 1998 ENGINE PERFORMANCE' 'General Motors Corp. - Theory & Operation - 4.3L

1998 ENGINE PERFORMANCE General Motors Corp. - Theory & Operation - 4.3L

INTRODUCTION This article covers basic description and operation of engine performance-related systems and components. Read this article before diagnosing vehicles or systems with which you are not completely familiar.

AIR INDUCTION SYSTEM AIRFLOW SENSING Speed Density

All engines are equipped with a Manifold Absolute Pressure (MAP) sensor and use the speed density method to compute airflow rate. PCM uses manifold pressure to calculate the airflow rate. The MAP sensor responds to manifold vacuum changes due to engine load and speed changes. The PCM sends a voltage signal to the MAP sensor. Manifold pressure changes result in resistance changes in the MAP sensor. By monitoring MAP sensor signal voltage, the PCM determines manifold pressure. If MAP sensor fails, the PCM supplies a fixed MAP sensor value, and uses the TP sensor to control fuel. Some models also use an Intake Air Temperature (IAT) sensor. Sensor allows PCM to determine intake air temperature. PCM uses signal to delay EGR until intake air temperature reaches about 40°F (5°C). If intake air temperature becomes excessively high, PCM compensates by slightly retarding timing.

COMPUTERIZED ENGINE CONTROLS The computerized engine control system monitors and controls a variety of engine/vehicle functions. The computerized engine control system is primarily an emission control system designed to maintain a 14.7:1 air/fuel ratio under most operating conditions. When the ideal air/fuel ratio is maintained, the Three-Way Catalytic (TWC) converter can control oxides of nitrogen (NOx), hydrocarbon (HC) and carbon monoxide (CO) emissions. The computerized engine control system consists of engine PCM/VCM, input devices (sensor and switch input signals) and output signals. POWERTRAIN CONTROL MODULE (PCM) & VEHICLE CONTROL MODULE VCM)

NOTE NOTE::

Mode Models ls are are equi equipp pped ed with with a Powe Powert rtrrain ain Cont Contro roll Modu Module le (PCM (PCM)) or a Vehi Vehicl cle e Control Module (VCM). The difference between VCM and PCM is the PCM controls electronic transmission internals, cooling fan and cruise control system. The VCM provides control of the engine systems as well as the antilock brake system. Unless stated otherwise, references to PCM also apply to VCM-equipped vehicles.

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For location of PCM/VCM, see COMPONENT LOCATIONS in I - SYSTEM/COMPONENT TESTS - 4.3L article. The PCM/VCM consists of the Arithmetic Logic Unit (ALU), Central Processing Unit (CPU), power supply and system memories. The PCM/VCM has a "learning" ability which allows it to make minor corrections for fuel system variations. If battery power is interrupted, a vehicle performance change may be noticed. PCM/VCM module corrects itself, and normal performance returns if vehicle is allowed to "relearn" optimum control conditions. "Relearning" occurs when vehicle is driven at normal operating temperature under part throttle, moderate acceleration and idle conditions. Arithmetic Logic Unit (ALU)

This internal component of the PCM/VCM converts electrical signals received from various engine sensors into digital signals for use by the CPU. Central Processing Unit (CPU)

CPU uses digital signals to perform all mathematical computations and logic functions necessary to deliver proper air/fuel mixture. CPU also calculates spark timing and idle speed. The CPU controls operation of emission control, "closed loop" fuel control and diagnostic system. Power Supply

Power for PCM/VCM reference output signals (5 volts) and control devices (12 volts) is received from the battery through ignition circuit when ignition switch is in ON position. Keep-alive memory power is received directly from the battery. Memories

PCM/VCM may use one or more of 5 types of memory: 

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Calibration Package (CALPAC) Some models use a PROM and a CALPAC. CALPAC provides fuel delivery back-up so engine runs in case of PROM or PCM/VCM failure. Any time PCM/VCM is replaced, PROM and CALPAC must both be installed into replacement unit. If battery voltage is removed, CALPAC information is retained. Electrically Erasable Programmable Read Only Memory (EEPROM) Some models may use an EEPROM. This is the same as a PROM except it can be electrically reprogrammed by the manufacturer using special equipment. Memory Calibration (MEM-CAL) Some vehicles may use a PCM/VCM containing a MEM-CAL unit. This assembly contains functions of PROM and CALPAC. If power to PCM/VCM is removed, MEM-CAL information is retained. MEMCAL also contains an internal Knock Sensor (KS) module on models equipped with a KS system. Programmable Read Only Memory (PROM) PROM is factory programmed engine calibration data which "tailors" PCM/VCM for specific transmission, engine, emission, vehicle weight and rear axle ratio application. The PROM can be

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© 2005 Mitchell Repair Information Company, LLC.


removed from PCM/VCM. If battery voltage is removed, PROM information is retained. 

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Random Access Memory (RAM) RAM is the scratch pad for the CPU. Data input, diagnostic codes and results of calculations are constantly updated and temporarily stored in RAM. If battery voltage is removed, all information stored in RAM is lost. Read Only Memory (ROM) ROM is programmed information which only PCM/VCM can read. The ROM program cannot be changed. If battery voltage is removed, ROM information is retained.

NOTE:

Components are grouped into 2 categories. The first category is INPUT DEVICES, consisting of components which control or produce voltage signals monitored by the control unit. The second category is OUTPUT SIGNALS, consisting of components controlled by the PCM/VCM.

INPUT DEVICES

Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input device usage on a specific model, see appropriate wiring diagram in L - WIRING DIAGRAMS - 4.3L article. The available input signals include: A/C On (A/C Request) Signal

The air conditioner "on" switch is mounted in instrument panel. This switch provides a simple "on" ("A/C request") signal, which is monitored by PCM/VCM. The PCM/VCM uses this signal to determine control of the A/C clutch relay (if equipped) and to adjust idle speed when A/C compressor clutch is engaged. On FWD Vans, control unit also activates radiator cooling fan when this signal is present. If this signal is not present on A/C equipped vehicles, vehicle may idle rough when A/C compressor cycles. To check function of the A/C switch, perform functional check of switch. See I - SYSTEM/COMPONENT TESTS - 4.3L article. Battery Voltage

Battery voltage is monitored by PCM/VCM. If battery voltage swings low, a weak spark or improper fuel control may result. To compensate for low battery voltage, PCM/VCM may increase idle speed, advance ignition timing, increase ignition dwell or enrich the air/fuel mixture. If voltage swings high, PCM/VCM may set a charging system fault code and turn on Malfunction Indicator Light (MIL). If voltage signal swings excessively low (less than 9 volts) or excessively high (16 volts, most models), PCM/VCM shuts down for as long as condition exists. If condition is short-term, MIL flickers and vehicle may stumble. Vehicle stalls if condition persists. Brake Switch Feedback

On models equipped with cruise control systems, PCM/VCM may monitor the brake switch circuit to determine when to engage and disengage cruise control. On vehicles equipped with a Torque Converter Clutch (TCC), one circuit of brake switch is in series with power supply for TCC solenoid located in automatic transmission. Luis Hurtado martes, 26 de enero de 2010 01:03:02 p.m.

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Camshaft Position (CMP) Sensor

CMP sensor utilizes a Hall Effect sensor that serves a similar function as Crankshaft Position (CKP) sensor. CMP sensor is mounted inside distributor. CMP sensor creates a 1X signal and is used by PCM/VCM to identify which cylinder(s) are misfiring. The 1X signal will not affect driveability. Cranking Signal

Cranking signal is a 12-volt signal monitored by the PCM. Signal is present when ignition switch is in the START position. The PCM/VCM uses signal to determine the need for starting enrichment. PCM/VCM also cancels diagnostics until engine is running and 12-volt signal is no longer present. Crankshaft Position (CKP) Sensor

CKP sensor utilizes a pick-up coil type sensor mounted on bottom of timing cover. The CKP sensor monitors crankshaft position and sends signals to ignition control module. These signals provide PCM/VCM with a TDC position reference for each piston, as well as supplying an engine speed (RPM) signal. This allows PCM to fire appropriate ignition coil at the proper time, determine triggering of the fuel injectors, and to compute crankshaft position and RPM. CKP sensor signal is also used to detect a cylinder misfire by monitoring changes in crankshaft speed. For additional information, see IGNITION SYSTEM . Digital Ratio Adapter Controller (DRAC)

DRAC compensates for various axle and tire ratios by monitoring the Vehicle Speed Sensor (VSS) signal and modifying it before passing it on to the PCM/VCM and speedometer. On models equipped with a DRAC, VSS buffer is an internal part of DRAC. Engine Coolant Temperature (ECT) Sensor

The ECT sensor is a thermistor (temperature sensitive resistor) located in an engine coolant passage. The PCM/VCM supplies and monitors a 5-volt signal to ECT sensor. This monitored 5-volt signal is then modified by resistance of the ECT sensor. When coolant temperatures are low, ECT sensor resistance is high and the PCM/VCM sees a high monitored voltage signal. When coolant temperatures are high, ECT sensor resistance is low and the PCM/VCM sees a low monitored voltage. When fully warmed, ECT sensor should reflect a temperature of at least 185°F (85°C). Coolant temperature input is used in the control of fuel delivery, ignition timing, idle speed, emission control devices and Torque Converter Clutch (TCC) application. An ECT sensor which is out of calibration will not set a Diagnostic Trouble Code (DTC), but can cause fuel delivery and driveability problems. An ECT sensor circuit problem should set a related DTC. Exhaust Gas Recirculation (EGR) Pintle Position

This sensor is mounted inside linear EGR valve and informs PCM/VCM of EGR pintle movement. PCM/VCM uses this information to control EGR flow. Fuel Pump Feedback


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PCM/VCM monitors fuel pump circuit between fuel pump relay/oil pressure switch and fuel pump. This enables the PCM/VCM to determine if fuel pump is being energized by fuel pump relay or back-up oil pressure switch. A failure in this monitored circuit results in the setting of a related diagnostic trouble code in PCM/VCM memory. Gear Switches

Gear switches are located inside automatic transmission. Switches may be normally open or closed, and change status depending upon internal hydraulic pressures. PCM/VCM uses high gear switch information in controlling emission components and engagement of Torque Converter Clutch (TCC). Intake Air Temperature (IAT) Sensor

IAT sensor is a thermistor (temperature sensitive resistor) mounted in the intake manifold. Low intake air temperature produces high internal sensor resistance, while high temperature causes low internal sensor resistance. The PCM/VCM supplies and monitors a 5-volt signal to sensor through a pull-down resistor in PCM/VCM. IAT sensor, also known as a manifold air temperature sensor, allows PCM/VCM to determine intake air temperature. PCM/VCM uses signal to delay EGR until intake air temperature reaches about 40°F (5°C). If intake air temperature becomes excessively high, PCM/VCM compensates by slightly retarding ignition timing. After a vehicle has cooled overnight, IAT and ECT sensor signals (resistance and temperature) should be close to same reading. Failure in IAT sensor circuit should set a related diagnostic trouble code. Knock Sensor (KS)

The knock sensor is a piezo-electric device which detects abnormal engine vibrations (spark knock) in the engine. This vibration results in the production of a very low AC signal, which is sent from the knock sensor to the KS module (integral to PCM/VCM). The PCM/VCM then retards ignition timing until the engine knock ceases. Two knock sensors are used on some models. A fault in the KS circuit may set a Diagnostic Trouble Code (DTC). See G - TESTS W/CODES - 4.3L article. When a related DTC is not present and the KS system is the suspected cause of a driveability problem, perform functional check of KS system. See I - SYSTEM/COMPONENT TESTS - 4.3L article. Manifold Absolute Pressure (MAP) Sensor

MAP sensor measures changes in manifold pressure. Changes in manifold pressure result from engine load and speed changes. The MAP sensor converts these changes in manifold pressure into a voltage output signal to PCM/VCM (1.5 volts at idle to about 4.5 volts at WOT). The PCM/VCM can monitor these signals and adjust air/fuel ratio and ignition timing under various operating conditions. If MAP sensor fails, the PCM/VCM substitutes a fixed MAP value, and uses the TP sensor to control fuel delivery. A fault in the MAP circuit should set a related Diagnostic Trouble Code (DTC). If a related DTC is not present and MAP sensor is suspected of causing a driveability problem, perform functional check of MAP sensor. See I - SYSTEM/COMPONENT TESTS - 4.3L article.


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CAUTION: Measure O2S voltage with a digital volt-ohmmeter (minimum 10-megohm impedance) only. Current drain of a conventional voltmeter could damage sensor. Oxygen Sensor (O2S)

O2S is mounted in exhaust system and monitors oxygen content of exhaust gases. The oxygen content causes the Zirconia/Platinum-tipped O2S to produce a voltage signal which is proportional to exhaust gas oxygen concentration (0-3%) compared to outside oxygen (20-21%). This voltage signal is low (about .1 volt) when a lean mixture is present and high (about 1.0 volt) when a rich mixture is present. As PCM/VCM compensates for a lean or rich condition, this voltage signal constantly fluctuates between high and low, crossing a .45-volt reference voltage supplied by PCM/VCM on the O2S signal line. This is referred to as "cross counts". The O2S does not function properly (produce voltage) until its temperature reaches 600°F (316°C). At temperatures less than the normal operating range of the sensor, vehicle functions in "open loop" mode, and PCM/VCM does not make air/fuel adjustments based upon O2S signals, but uses TP and MAP or MAF values to determine air/fuel ratio from a table built into memory. When PCM/VCM reads a voltage signal greater than .45 volt from the O2S, PCM/VCM begins to alter commands to injector to produce a leaner mixture. Once vehicle has entered "closed loop" mode, a fault in the O2S circuit (cooled-down sensor or open or shorted O2S circuit) will return vehicle to "open loop" mode. A problem in the O2S circuit should set a related diagnostic trouble code. On most engines, O2S uses an internal heating element. This type of sensor is referred to as a Heated Oxygen Sensor (HO2S). Heating element allows HO2S to warm more quickly, causing fuel system to enter "closed loop" mode sooner. Heating element also prevents fuel system from re-entering "open loop" mode, which would be a normal response to prolonged idling. Park/Neutral Position (PNP) Switch

This switch is connected to transmission gear selector and signals PCM/VCM when transmission is in Park or Neutral. PCM/VCM uses this information for determining control of ignition timing, Torque Converter Clutch (TCC) and idle speed. To check function of PNP switch, perform functional check of switch. See I SYSTEM/COMPONENT TESTS - 4.3L article. Transmission Fluid Pressure (TFP) Switch (4L60-E & 4L80-E Transmission)

The TFP is actually 5 pressure switches combined into a single unit mounted on transmission valve body. The PCM/VCM supplies battery voltage on 3 separate wires to TFP. As switches are actuated in various combinations during transmission operation, PCM/VCM can detect what gear range transmission is in. Throttle Position (TP) Sensor

TP sensor is a variable mechanical resistor connected directly to throttle shaft linkage. TP sensor has 3 wires connected to it. One is connected to a 5-volt reference voltage supply from PCM/VCM, another is connected to PCM/VCM ground and third is a signal return which is monitored by PCM/VCM. Voltage signal from TP sensor varies from closed throttle (0.5-1.0 volt) to wide open throttle (4.5-5 volts). PCM/VCM uses this signal Luis Hurtado martes, 26 de enero de 2010 01:03:02 p.m.

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to determine control of fuel, idle speed, spark timing and Torque Converter Clutch (TCC). A problem in TP sensor circuit may set a related diagnostic trouble code. Transmission Fluid Temperature (TFT) Sensor (4L60-E, 4L80-E & 4T60-E Transmission)

TFT sensor is a thermistor (temperature sensitive resistor) mounted to the transmission valve body. The PCM/VCM supplies and monitors a 5-volt signal to TFT sensor. This monitored 5-volt signal is then modified by resistance of TFT sensor. When transmission fluid temperatures are low, TFT sensor resistance is high and PCM/VCM sees a high monitored voltage signal. When transmission fluid temperatures are high, TFT sensor resistance is low and PCM/VCM sees a low monitored voltage. PCM/VCM uses TFT sensor input to control Torque Converter Clutch (TCC) application and shift quality. Sensor circuit problem should set a related diagnostic trouble code. Vehicle Speed Sensor (VSS)

VSS is a Permanent Magnet (PM) generator mounted in transmission or transfer case. The VSS sends a pulsing signal to the PCM/VCM or Digital Ratio Adapter Controller (DRAC), which passes the signal on to the PCM/VCM. The PCM/VCM then converts this signal into miles per hour by monitoring the time interval between pulses. PCM/VCM uses this sensor input in controlling Torque Converter Clutch (TCC) engagement, shift speed, etc. OUTPUT SIGNALS

NOTE:

Models have different combinations of computer-controlled components. Not all listed components are used on every model. For theory and operation of components, refer to indicated system.

A/C Clutch Relay

See MISCELLANEOUS PCM/VCM CONTROLS . Cruise Control Stepper Motor

See MISCELLANEOUS PCM/VCM CONTROLS . Malfunction Indicator Light (MIL)

See SELF-DIAGNOSTIC SYSTEM . EGR System

See EMISSION SYSTEMS . Electronic Ignition (EI)

See IGNITION SYSTEM . Luis Hurtado martes, 26 de enero de 2010 01:03:02 p.m.

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Fuel Injectors

See FUEL CONTROL under FUEL SYSTEM. Fuel Pump & Fuel Pump Relay

See FUEL DELIVERY under FUEL SYSTEM. Idle Air Control (IAC) Valve

See IDLE SPEED under FUEL SYSTEM. Self-Diagnostics

See SELF-DIAGNOSTIC SYSTEM . Serial Data

See SELF-DIAGNOSTIC SYSTEM . Shift Solenoids (4L60-E, 4L80-E & 4T60-E Transmission)

See MISCELLANEOUS PCM/VCM CONTROLS . Torque Converter Clutch (TCC)

See MISCELLANEOUS PCM/VCM CONTROLS . Transmission Shift Light (Manual Transmission)

See MISCELLANEOUS PCM/VCM CONTROLS .

FUEL SYSTEM FUEL DELIVERY Fuel Pump

An in-tank, electric fuel pump delivers fuel to injector(s) through an in-line fuel filter. The pump is designed to supply fuel pressure in excess of vehicle requirements. The pressure relief valve controls maximum fuel pump pressure. On Central Sequential Port Injection (CSI) systems, pressure regulator is mounted to fuel metering body under upper intake manifold. On Sequential Multiport Fuel Injection (SFI), pressure regulator is attached to end of fuel rail. Pressure regulator keeps fuel available to injector(s) at a constant pressure. Excess fuel is returned to fuel tank through pressure regulator return line.


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When ignition switch is turned to ON position, PCM/VCM turns on electric fuel pump by energizing fuel pump relay. PCM/VCM keeps pump on if engine is running or cranking (PCM/VCM is receiving reference pulses from ignition module). If there are no reference pulses, PCM/VCM turns pump off within 2 seconds after ignition is turned on. Most models also include a second control path through the oil pressure switch which will turn the fuel pump on after the switch detects oil pressure. Cranking time will be longer if fuel pump does not receive current until oil pressure switch contacts close. Fuel Pressure Regulator (CSI)

Fuel pressure regulator is a diaphragm-operated relief valve with injector pressure on one side and manifold pressure (vacuum) on the other. Pressure regulator maintains a pressure of 60-66 psi (4.2-4.6 kg/cm 2 ) under all operating conditions. Pressure regulator is a factory preset, nonadjustable, spring-loaded diaphragm attached to CSI assembly. Spring tension maintains a constant fuel pressure to injector regardless of engine load. Fuel Pressure Regulator (SFI)

Fuel pressure regulator is a diaphragm-operated relief valve with injector pressure on one side and manifold pressure (vacuum) on the other. Pressure regulator maintains a pressure of 56-62 psi (3.9-4.4 kg/cm 2 ) under all operating conditions. Pressure regulator compensates for engine load by increasing fuel pressure when low manifold vacuum is experienced. Fuel Pump Relay

When ignition switch is turned to ON position, PCM/VCM turns electric fuel pump on by energizing fuel pump relay. PCM/VCM keeps relay energized if engine is running or cranking (PCM/VCM is receiving reference pulses from ignition module). If there are no reference pulses, PCM/VCM turns pump off within 2-20 seconds after key on. As a back-up system to fuel pump relay, the oil pressure switch also activates fuel pump. The oil pressure switch is normally open until oil pressure reaches about 4 psi (.28 kg/cm 2 ). If fuel pump relay fails, the oil pressure switch closes when oil pressure is obtained and operates the fuel pump. Cranking time will be longer if fuel pump does not receive current until oil pressure switch contacts close. Oil pressure switch may be combined into a single unit with an oil pressure gauge sending unit or sensor. PCM/VCM monitors fuel pump circuit between fuel pump relay/oil pressure switch and fuel pump, enabling PCM/VCM to determine if fuel pump is being energized by fuel pump relay or oil pressure switch. A failure in this monitored circuit results in the setting of a related diagnostic trouble code in PCM/VCM memory. For additional information on fuel pump activation, see basic testing procedures in F - BASIC TESTING - 4.3L and also see system testing procedures in I - SYSTEM/COMPONENT TESTS - 4.3L articles. FUEL CONTROL

The PCM/VCM, using input signals, determines adjustments to the air/fuel mixture to provide the optimum ratio for proper combustion under all operating conditions. Fuel control systems can operate in the "open loop" Luis Hurtado martes, 26 de enero de 2010 01:03:03 p.m.

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or "closed loop" mode. Open Loop

When engine is cold and engine speed is greater than 400 RPM, PCM/VCM operates in "open loop" mode. In "open loop" mode, PCM/VCM calculates air/fuel ratio based upon coolant temperature and MAP or MAF sensor readings. Engine remains in "open loop" mode until O2S reaches operating temperature, coolant temperature reaches a preset temperature and a specific period of time has elapsed after engine starts. Closed Loop

When O2S reaches operating temperature, coolant temperature reaches a preset temperature and a specific period of time has passed since engine start-up, PCM/VCM operates in "closed loop" mode. In "closed loop" mode, PCM/VCM controls air/fuel ratio based upon O2S signals (in addition to other input parameters) to maintain as close to a 14.7:1 air/fuel ratio as possible. If O2S cools off (due to excessive idling) or a fault occurs in O2S circuit, vehicle will re-enter "open loop" mode. On most engines, O2S is equipped with an internal heating element. This type of sensor is known as a Heated Oxygen Sensor (HO2S). The heating element enables system to reach and maintain "closed loop" mode sooner, even during periods of extended idle. Central Sequential Port Injection (CSI)

CSI is a non-repairable injector assembly consisting of a fuel meter body, fuel pressure regulator, fuel injector and poppet nozzles with fuel tubes. CSI assembly is housed in the lower manifold assembly. Fuel pump and pressure regulator maintain fuel pressure at 60-66 psi (4.2-4.6 kg/cm 2 ) under all operating conditions. When injector is energized, pressurized fuel passes down fuel distribution tubes to poppet nozzles located at rear of intake valves. Fuel pressure forces poppet valves open, spraying fuel into cylinders when intake valves are open. As fuel pressure drops (due to all poppets opening or injector de-energizing), poppet nozzle spring pressure closes poppet nozzle until pressure again builds high enough to overcome poppet nozzle spring pressure. Excess fuel is returned to the fuel tank via the fuel return line. Sequential Fuel Injection (SFI)

Injectors on these models are pulsed sequentially in spark plug firing order. Main differences between sequential and simultaneous systems are injectors, wiring and the PCM/VCM. Constant fuel pressure is maintained to the injectors. Air/fuel mixture is regulated by amount of time injector stays open (pulse width). Various sensors provide information to the PCM/VCM to control pulse width. Fuel System Operating Modes

Internal PCM/VCM calibration controls fuel delivery during starting, clear flood mode, deceleration and heavy acceleration. 

Starting


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During engine starts, PCM/VCM delivers one injector pulse for each distributor reference pulse received (synchronized mode). Injector pulse width is based upon coolant temperature and throttle position. PCM/VCM determines air/fuel ratio when throttle position is less than 80 percent open. Engine starting air/fuel ratio ranges from 0.8:1 at -40°F (-40°C) to 16.8:1 at 230°F (110°C). At lower coolant temperatures, injector pulse width is wider (richer air/fuel mixture ratio). When coolant temperature is high, injector pulse width becomes narrower (leaner air/fuel ratio). 

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Clear Flood If engine is flooded, driver must depress accelerator pedal to Wide Open Throttle (WOT) position. At this position, PCM/VCM adjusts injector pulse width equal to an air/fuel ratio of 16.5:1. This air/fuel ratio is maintained as long as throttle remains in wide open position and engine speed is less than 600 RPM. If throttle position becomes less than 65 percent open and/or engine speed exceeds 600 RPM, PCM/VCM changes injector pulse width to that used during engine starting (based upon coolant temperature and manifold vacuum). Heavy Acceleration PCM/VCM provides fuel enrichment during heavy acceleration. Sudden opening of throttle valve causes rapid increase in MAP or MAF signal. Pulse width is directly related to MAP or MAF, throttle position and coolant temperature. Higher MAP or MAF and wider throttle angles give wider injector pulse width (richer mixture). During enrichment, injector pulses are not in proportion to distributor reference signals (non -synchronized). Any reduction in throttle angle cancels fuel enrichment. Deceleration During normal deceleration, fuel output is reduced. This reduction in available fuel serves to remove residual fuel from intake manifold. During sudden deceleration, when MAP or MAF, throttle position and engine speed are reduced to preset levels, fuel flow is cut off completely. This deceleration fuel cut-off overrides normal deceleration mode. During either deceleration mode, injector pulses are not in proportion to distributor reference signals. Battery Voltage Correction PCM/VCM compensates for low battery voltage by increasing injector pulse width and increasing idle RPM. PCM/VCM is able to perform these commands because of a built-in memory/learning function. Fuel Cut-Off When ignition is turned off, injectors are de-energized to prevent dieseling. Injectors are not energized if RPM reference pulses are not received by the PCM/VCM, even with ignition on. This prevents flooding before starting. Fuel cut-off also occurs at high engine RPM or excessive vehicle speed to prevent internal damage to engine. Some models may also cut off fuel injector signals during periods of sudden, closed throttle deceleration (when fuel is not needed).

IDLE SPEED

PCM/VCM controls engine idle speed depending upon engine operating conditions. PCM/VCM senses engine operating conditions and determines best idle speed. Idle Air Control (IAC) Valve


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The IAC valve controls engine idle speed to prevent stalling during engine load changes. The IAC valve is mounted on throttle body and controls the amount of air by-passed around the throttle plate. The IAC valve controls engine idle speed by moving its pintle in and out in steps referred to as "counts" (0 counts, fully seated; 255 counts, fully retracted). Counts can be measured by observing scan tool display while connected to the Data Link Connector (DLC). If engine RPM is too low, pintle is retracted and more air is by-passed around the throttle plate to increase engine RPM. If engine RPM is too high, pintle is extended and less air is by-passed around the throttle plate to decrease engine RPM. Normal counts on an idling engine should be near 18. When engine is idling, PCM/VCM determines proper positioning of IAC valve based on battery voltage, coolant temperature, engine load and engine RPM. If IAC valve is disconnected or reconnected with engine running, IAC loses its reference point and must be reset. On some models, IAC is reset by turning ignition on, then off. Other models require driving vehicle at normal operating temperature over 35 MPH with circuit properly connected. Problems in IAC circuit should set a related diagnostic trouble code. The IAC valve affects only the idle system. If valve is stuck fully open, excessive airflow into the manifold creates a high idle speed. Valve stuck closed allows insufficient airflow, resulting in low idle speed. For calibration purposes, several different IAC valves are used. Ensure replacement valve is proper design.

IGNITION SYSTEM Enhanced Ignition System

The enhanced ignition system consists of the VCM, distributor, ignition coil driver module, ignition coil and Camshaft Position (CMP) sensor. Ignition control and by-pass functions are controlled by the VCM. 

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Camshaft Position (CMP) Sensor CMP sensor is similar to CKP sensor. CMP sensor provides one pulse (1X signal) per camshaft revolution. VCM uses this signal in conjunction with the crankshaft position to determine which cylinder (s) are misfiring. Crankshaft Position (CKP) Sensor CKP sensor is located in the front engine cover. Air gap between sensor and target wheel is preset and is not adjustable. Target wheel has 4 slots, 60 degrees apart, and is keyed to the crankshaft. Rotation of target wheel creates a change in the magnetic field of the sensor which results in an induced voltage pulse. One crankshaft revolution will result in 4 pulses (4X signal). Based on these pulses, VCM is able to determine crankshaft position and engine speed. VCM will then activate the fuel injector and provide spark to distributor. Distributor Distributor assembly contains the Camshaft Position (CMP) sensor, cap, rotor and shaft. A Diagnostic Trouble Code (DTC) will set when distributor is installed a tooth off in relation to the camshaft. Distributor is not serviceable. Ignition Coil Driver Module


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Module is mounted next to coil. VCM signals the ignition coil driver to turn on primary current to the ignition coil by pulling the IC line high (4 volts). The ignition control driver turns the primary current on and off by applying and removing ground to primary winding. Module does not have a back-up function that would allow engine to run if IC signal is lost. Ignition Timing Control

Ignition spark timing and ignition dwell time are entirely controlled by the PCM/VCM. The PCM/VCM monitors information from various engine sensors, computes the desired spark timing and dwell, and firing of the ignition coil via IC line to the coil driver.

EMISSION SYSTEMS CATALYTIC CONVERTER

A Three-Way-Catalytic (TWC) converter is used to reduce exhaust emissions. This type of converter can reduce hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx). The upstream section of the converter contains a reducing/oxidizing bed to reduce NOx while oxidizing HC and CO. An air supply pipe from the air injection system injects air between the beds of the converter. Thus, the second converter bed oxidizes any remaining HC and CO to efficiently reduce exhaust emissions. EXHAUST GAS RECIRCULATION (EGR)

The Exhaust Gas Recirculation (EGR) system is designed to reduce oxides of nitrogen (NOx) emissions by lowering combustion temperatures. A metered amount of exhaust gas is recirculated into the intake manifold and mixed with the air/fuel mixture. A linear EGR valve is used on all engines. EGR valve includes electric motor to raise and lower EGR valve pintle and internal EGR valve pintle position sensor. EGR valve pintle is used to control EGR flow. PCM/VCM controls pintle based on engine temperature, engine RPM and EGR valve pintle position sensor inputs. EVAPORATIVE EMISSION SYSTEM

All vehicles use carbon canister storage for evaporative fuel control. Evaporative emission control system stores gasoline fumes from fuel tank in a carbon canister. After engine is running, fumes are drawn into engine for burning during combustion process. The basic components used in the evaporative emission system are an activated carbon canister (all models, open at top or bottom for fresh air intake), vacuum operated canister control valve (some Federal models), or purge control solenoid (all other models). For specific component application and vacuum hose routing, see M VACUUM DIAGRAMS - 4.3L article. Carbon Canister

Evaporative fumes from the fuel tank are vented through hose(s) into a canister containing activated carbon. Activated carbon absorbs and holds fuel vapors when engine is not operating. When engine is started and Luis Hurtado martes, 26 de enero de 2010 01:03:03 p.m.

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engine speed is greater than idle (purge at idle would cause too rich a mixture), engine vacuum draws fuel vapors from canister into engine. A vacuum canister purge valve or purge control solenoid regulates vapors through this purge line. Carbon canisters are open in design. When engine is started, engine vacuum draws outside air into canister either through top or bottom, then through a filter in bottom of canister. This helps to purge vapors from the activated carbon. Canister Purge Control Solenoid (CPCS)

CPCS allows fuel vapor to flow from carbon canister to the engine. Solenoid is normally closed and is pulsewidth modulated by the PCM/VCM to precisely control vapor flow. PCM/VCM controls flow of fuel vapors based on coolant temperature. At temperatures greater than 113°F (45°C), purge control solenoid is open. Purge control solenoid is also opened if PCM/VCM detects extreme lean air/fuel mixture ratio conditions. POSITIVE CRANKCASE VENTILATION (PCV)

The PCV system provides effective evacuation of crankcase vapors. Fresh air from the air filter housing is supplied to the crankcase, where it is mixed with blow-by gases and passed through the PCV valve and into the intake manifold. This mixture is then passed into the combustion chamber and burned. The PCV valve provides primary control in this system by metering the flow (according to manifold vacuum) of the blow-by vapors. When manifold vacuum is high (at idle), the PCV valve restricts the flow to maintain a smooth idle. Under conditions in which abnormal amounts of blow-by gases are produced (such as worn cylinders or rings), system is designed to allow excess gases to flow back through crankcase vent hose into air inlet. Spring pressure holds PCV valve closed when engine is not running. This prevents hydrocarbon fumes from collecting in the intake manifold, a condition which could result in hard starting. During engine operation, manifold vacuum pulls the valve closed against spring pressure. As vacuum decreases with increased engine load (ROM), spring pressure begins to overpower vacuum strength. This allows PCV valve to open proportional to engine load and evacuation requirements. Should the engine backfire, the PCV valve closes to prevent ignition of fumes in crankcase.

SELF-DIAGNOSTIC SYSTEM The PCM/VCM is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, PCM/VCM will illuminate the Malfunction Indicator Light (MIL) located on instrument cluster. When a malfunction is detected and MIL is turned on, a corresponding Diagnostic Trouble Code (DTC) will be stored in PCM/VCM memory. Malfunctions are designated as either "emission related" or as "nonemission related", and are divided into 4 code types to identify type of fault. The 4 code types are defined as follows: 

Type "A" Emission related faults that illuminate MIL at first occurrence of a fail condition.


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





Type "B" Emission related faults that illuminate MIL if a fault occurs in 2 consecutive ignition cycles. Type "C" Non-emission related faults that illuminate MIL only when fault is present. MIL will turn off 3 seconds after engine start if fault is no longer present, but a record of fault will remain stored in memory. Type "D" Non-emission related faults which do not illuminate MIL. Emission related DTCs (type "A" or "B") cause MIL to illuminate and remain on until the malfunction is repaired. On models using digital display on dash to indicate DTCs, DTCs may be accompanied by "current" or "history" indication for intermittent and hard failures. If MIL comes on and remains on during vehicle operation, cause of malfunction must be determined using appropriate diagnostic procedure for affected DTC located in G - TESTS W/CODES - 4.3L article. If a sensor fails, PCM will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional but loss of good driveability is likely.

Non-emission related DTCs (type "C") cause MIL to flicker or glow and go out about 10 seconds after the intermittent fault goes away. The corresponding DTC, however, will be retained in PCM/VCM memory. On models using digital display on dash to indicate DTCs, DTCs may be accompanied by a "current" or "history" indication for intermittent and hard failures. If related DTC does not reoccur within 50 engine restarts, related DTC will be erased from PCM/VCM memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See TROUBLE SHOOTING - BASIC PROCEDURES article. MALFUNCTION INDICATOR LIGHT (MIL)

As a bulb and system check, MIL will illuminate when ignition switch is turned to ON position and engine is not running. When engine is started, MIL should go out. If MIL does not go out, a malfunction has been detected in the computerized engine control system or MIL circuit is faulty. MIL may be used on some models to display a stored Diagnostic Trouble Code (DTC). To access DTCs, see I - SYSTEM/COMPONENT TESTS - 4.3L article. SERIAL DATA

PCM/VCM has a serial data line. Serial data is a stream of electrical impulses which can be exchanged between control modules. Serial data can be interpreted using a special scan tool. Access serial data by connecting a scan tool to Data Link Connector (DLC). Update intervals and information contained within data stream vary with model application.

MISCELLANEOUS PCM/VCM CONTROLS NOTE:

Although not considered true engine performance-related systems, some devices may affect driveability if they malfunction.

A/C CLUTCH

On most models, PCM/VCM regulates operation of the A/C clutch through a relay. The PCM/VCM disengages Luis Hurtado martes, 26 de enero de 2010 01:03:03 p.m.

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the A/C compressor when compressor load on engine may cause driveability problems (i.e., during hot restart, idle, low speed steering maneuvers and wide open throttle operation) or if A/C refrigerant pressure drops to less than or rises to greater than normal operating levels. Refrigerant pressure is sensed through the monitoring of high and low pressure switches or a pressure sensor which registers either high or low pressure levels. Hot restart is monitored through the coolant temperature sensor. For component application and related wiring, see A/C-HEATER SYSTEM - MANUAL article in the AIR CONDITIONING & HEAT section for additional information. A/C Pressure Switches

A/C high and low pressure switches may be used in the A/C compressor clutch or compressor clutch relay circuit. Switches are normally closed, completing the circuit which energizes the compressor clutch. When system refrigerant pressure increases beyond a certain point, high side switch opens, causing compressor clutch to disengage. If system refrigerant level decreases (causing freon pressure to drop), low side pressure switch opens, preventing compressor damage by causing compressor clutch to disengage. CRUISE CONTROL

On models equipped with cruise control, the system is operated by the PCM/VCM. PCM/VCM receives inputs from VSS, servo diaphragm position sensor, cruise control switch and brake release switch. Based on these inputs, PCM/VCM controls position of cruise control stepper motor. PCM/VCM prevents system engagement at speeds of less than 25 MPH. PCM/VCM is not serviceable; if defective, it must be replaced. A system fault is stored as a Diagnostic Trouble Code (DTC) in PCM/VCM memory. TRANSMISSION Torque Converter Clutch (TCC)

The transmission/transaxle TCC eliminates power loss of torque converter stage when vehicle is in a cruise condition, allowing driver the convenience of an automatic transmission while providing the fuel economy of a manual transmission. Fused battery ignition is supplied to TCC solenoid through a brake switch. On some models, 2nd, 3rd and 4th gear hydraulic apply switches (located within transmission) may also be in series with solenoid power or ground circuit. On other models, switch status may only be monitored by PCM/VCM, without sharing power or ground with TCC solenoid. For wiring reference, see AUTO TRANS DIAGNOSIS - 4L60-E (4.3L) article in AUTO TRANS DIAGNOSIS section. The TCC engages when vehicle is moving faster than a pre-calibrated speed, engine is at normal operating temperature, throttle position sensor output is not changing (indicating a steady road speed) and transmission 3rd gear or high gear switch (if equipped) and brake switch are closed. When vehicle speed is great enough (about 20-45 MPH as indicated by the vehicle speed sensor), PCM/VCM energizes TCC solenoid mounted in transmission, allowing torque converter to directly connect engine to the transmission. When operating conditions indicate transmission should operate as normal, TCC solenoid is deLuis Hurtado martes, 26 de enero de 2010 01:03:03 p.m.

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energized, allowing transmission to return to normal automatic operation. Since power for the TCC solenoid is delivered through the brake switch, transmission also returns to normal automatic operation when brake pedal is depressed. To check function of TCC system, perform functional check of system. See MISCELLANEOUS PCM/VCM CONTROLS in I - SYSTEM/COMPONENT TESTS - 4.3L article. Electronic Transmission (4L60-E, 4L80-E & 4T60-E)

On most vehicles, PCM/VCM controls transmission and other vehicle functions. PCM/VCM monitors a number of engine/vehicle functions and uses data to control shift solenoid "A", shift solenoid "B", TCC solenoid and the force motor. PCM/VCM also regulates TCC engagement, upshift pattern, downshift pattern and line pressure (shift quality). 





Shift Solenoid "A" (1st-2nd) Shift solenoid "A" is attached to the valve body and is a normally-open exhaust valve. PCM/VCM activates solenoid by grounding it through an internal quad-driver. Solenoid "A" is on in 1st and 4th gears, but off in 2nd and 3rd. When on, solenoid redirects fluid to act on the shift valves. Shift Solenoid "B" (2nd-3rd) Shift solenoid "B" is attached to the valve body and is a normally-open exhaust valve. PCM/VCM activates solenoid by grounding it through an internal quad-driver. Solenoid "B" is on in 3rd and 4th gears, but off in 1st and 2nd. When on, solenoid redirects fluid to act on the shift valves. Force Motor (Pressure Control Solenoid) Force motor is attached to valve body and controls line pressure by moving a pressure regulator valve against spring pressure. Force motor replaces throttle valve or vacuum modulator used on past transmissions. PCM/VCM varies line pressure based upon engine load. Engine load is calculated from various inputs, especially TP sensor. Line pressure is actually varied by changing amperage applied to force motor from zero (high pressure) to 1.1 amps (low pressure). Force motor is periodically pulsed to prevent fluid contamination or tarnish from causing pressure regulator valve to stick.

Shift Light

Shift light may be used on vehicles equipped with manual transmission. Light indicates best transmission shift point for maximum fuel economy. Power for light is supplied through GAUGES fuse. Light illuminates when PCM/VCM supplies a ground circuit for bulb. For wiring reference, see wiring schematic under MISCELLANEOUS PCM/VCM CONTROLS in I - SYSTEM/COMPONENT TESTS - 4.3L article.


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Motor 4.3L (Blazer 98) - Teoria y Funcionamiento

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