GM Powertrain Performance 2 Gasoline and environmental concerns: Development of cleaner burning fuels Balance environmental objectives with performance-based standards Regulations set specifications to control environmental impact Specifications/guidelines control gasoline characteristics to ensure performance Gasoline and environmental concerns: Development of cleaner burning fuels Balance environmental objectives with performance-based standards Regulations set specifications to control environmental impact Specifications/guidelines control gasoline characteristics to ensure performance Gas octane: Measure of anti-knock quality Two fuels of same octane can have different energy content Fuel energy content is measured in BTUs Higher BTU means better fuel economy rating Higher compression ratio requires higher octane Volatility: Fuel's ability to vaporize More volatile components evaporate at lower temperatures Less volatile components evaporate at higher temperatures Gasoline not volatile enough results in poor cold starts and poor warm-up drivability Gasoline too volatile vaporizes too easily and may boil in fuel line at high operating temperatures Reid vapor pressure (RVP): Measure of how easily fuel will vaporize Low RVP indicates low volatility High RVP indicates high volatility Winter fuel blend is more volatile (high RVP) Summer fuel blend is less volatile (low RVP) Oxygenated fuels: Ethanol Methyl Tertiary Butyl Ether (MTBE) Ethyl Tertiary Butyl Ether (ETBE) Use controlled by EPA Important - GM vehicles are not designed for fuel that contains methanol. Methanol can corrode metal parts and damage rubber and plastic parts. Throttle body injection (TBI): Introduced in 1980 on 6.0L V-8 Fuel is atomized better during cold starts and warm-up Mixture enrichment is kept to a minimum during cold starts Throttle is only mechanical linkage Air/fuel mixture distribution more consistent Improved fuel economy Reduced emissions Fuel injected into throttle bores and delivered through intake manifold to engine TBI unit consists of fuel meter body and throttle body Fuel meter body has either single bore and one injector, or dual bores and two injectors Throttle body components: Throttle position sensor Idle air control valve Vacuum ports for MAP sensor, EGR, and EVAP canister purge Features of the Model 300 and 500: Single TBI systems used on 4-cylinders through 1986 Same except for location of throttle lever and TP sensor, type of inlet fitting, and position of IAC valve Model 700 TBI assembly: Used on 4-cylinder engines beginning in 1987 Single-injector unit Either adjustable or non-adjustable TP sensor Fuel pressure regulator serviceable under external cover Injector is Multec ball-and-seat design Some applications have internal constant pressure bleed passage TBI operation: Pressurized fuel enters TBI unit from pressure line and passes through inlet filter Injector is pulsed on and off Fuel is atomized and sprayed into throttle body in a conical pattern Excess fuel flows past pressure regulator into return line and back to fuel tank Pressure regulator: Maintains constant fuel pressure at injector tips Normally between 9 and 13 psi 26-32 psi on 1990-92 Lumina and 1994-95 7.4L truck due to hot fuel vapor conditions TBI injector: Electromagnetic device containing a solenoid, consisting of coil and core PCM energizes coil Core is lifted up, moving ball valve off its seat Fuel is directed through spray tip into throttle body Multiport fuel injection (MFI): Introduced in 1984 on 1.8L L4 and 3.8L V-6 engines Provides better overall performance and fuel economy compared to TBI Uses one injector per cylinder Narrow cone of atomized fuel is injected into intake manifold Used on all passenger car and truck engines Engine torque output is increased due to: Ram tuning for denser air charge to cylinders Lower air/fuel mixure temperatures Emissions performance improved due to: Enhanced air/fuel distribution Eliminating problems of fuel condensation Leaner operation during warm-up Improved airflow sensing Improved fuel economy from: Lower axle ratios More precise fuel flow management Multiport fuel injection (MFI): Each cylinder has individual injector Can be pulsed simultaneously or in groups Sequential fuel injection (SFI): Pulses injectors one at a time, in engine-firing sequence Central multiport fuel injection (CMFI): One throttle-body type injector solenoid for all poppets One poppet valve for each cylinder Central sequential multiport fuel injection (CSFI): One electrical injector for each poppet nozzle One poppet valve for each cylinder Each is fired sequentially Specific injector operation: Simultaneous - all energised at the same time "double fire" Alternating double-fire Group-timed Sequential fuel injection Simultaneous fuel injection systems: All injectors are energized once per crankshaft revolution Each port gets two injections of fuel during each cycle Sequence also known as double-fire injection Alternating double-fire injection: Two of the four injectors are energized every 180° of crankshaft rotation Each pair is triggered twice per combustion cycle Injectors are paired: #1 and #4 #2 and #3 Group-timed fuel injection: Injector group A (cylinders 1, 3, 5, and 7) controlled by one PCM driver circuit Injector group B (cylinders 2, 4, 6, and 8) controlled by another PCM driver circuit Allows PCM to manage each cylinder bank separately MFI throttle body: Primary function is to meter incoming air Houses TP sensor and IAC valve Has coolant passages to prevent throttle icing MFI fuel system fuel rail: Fastened to manifold Holds fuel injectors in position and carries pressurized fuel "O" rings prevent leaks and insulate injectors from vibration and heat Pressure tap used to check or relieve system pressure Fuel pressure regulator: Located on return side of fuel rail Maintains constant fuel pressure across injectors Has chamber separated by a diaphragm: Fuel on one side Engine vacuum on second side Calibration spring located on vacuum side Manifold pressure: Could affect fuel flow from injector Fuel pressure varied to compensate for changes by using engine vacuum Increased fuel pressure can compensate for increased manifold pressure at injector tip Service specifications based on fuel pump running with zero vacuum applied to regulator Demand fuel system pressure regulator: Located in fuel return line inside fuel tank No vacuum line is connected to regulator port Fuel pressure remains constant 55 - 60 psi with pump running Be sure to refer to current service information procedures Electronically controlled fuel injectors: One per cylinder Operate under PCM control Bosch injector: Uses pintle valve and seat Has diffuser below valve seat Multec injector: Stainless steel ball and seat valve Director plate with six holes provides spray pattern control Less susceptible to plugging caused by varnish buildup Bosch chimney design injector: "Chimney" surrounding pintle Reduced varnish buildup Machined-in longitudinal fuel passage in manifold Bosch feed port injector: Used on 2.2 liter engine Fuel enters bottom pintle and seat Fuel rail eliminated Multec injector design: Used on 3.4L, DOHC V6 Has four holes and "directed" fuel spray pattern Ensures even fuel distribution between both intake valves Multec II injectors: Outside diameter about half of Multec I injector Improved fuel targeting Sealed solenoid coil and bobbin prevents corrosion Central multiport fuel injection (CMFI): Hybrid of multiport and throttle body injection Throttle body type injector solenoid meters fuel supply to poppet valves for each cylinder CMFI assembly consists of: Low-impedance injector solenoid Low-gain fuel pressure regulator Six poppet nozzles that deliver calibrated fuel Injector solenoid: Single-disc, centrally mounted Controlled by PCM Six hole distributor gasket Six fuel meter body passages Six individual poppet nozzle tubes Pressure regulator: Low-gain Maintains calibrated fuel pressure of 370 to 440 kPa (54 to 64 psi) Maintains balance between fuel flow and spring force to regulate pressure Poppet nozzle: Check ball Extension spring Fuel flows from poppet nozzle when pressure exceeds 254 - 296 kPa (37 - 43 psi) Injector solenoid energized: Fuel enters poppet nozzle, increasing pressure Pressure overcomes spring force, causing ball at end of poppet nozzle to unseat Fuel then sprays into cylinder Central sequential fuel injection: Used on light trucks beginning in 1996 Similar to CMFI system One electrical injector for each poppet nozzle Each nozzle is fired sequentially for accuracy and precise metering control CSFI body assembly: Fuel injectors Fuel pressure regulator Fuel inlet and return ports Electrical connector Fuel meter body numbered to indicate poppet nozzle order When injector energizes: Increased fuel pressure pushes that poppet nozzle's ball off its seat Fuel is supplied for cylinder When injector de-energizes: Spring force overcomes fuel pressure and ball seats Cuts off fuel supply at nozzle New injection system LU3: Replaces poppet nozzles with Multec II injectors Removes injectors from CSFI body PCM: Responsible for monitoring inputs and outputs Has direct effect on engine operation DLC - Data Link Connector Powertrain control module (PCM): Operates entire engine management system Requires power to process and control engine management system: Supplied system voltage through 10 amp fuse when on Constant battery feed is provided to PCM through separate 20 amp fuse when off PCM ground circuit: Has at least two circuits from PCM Perform checks during diagnosis: Use high impedance (10 megaohms) digital voltmeter J-39200 Verify that PCM ignition feed and memory circuits have sufficient voltage Check for high resistance on ground side of PCM PCM operation: Either in Open Loop or Closed Loop Delivers correct ignition advance and fuel to engine under all operating conditions: Cold engine requires rich fuel mixture to start As engine warms fuel mixture is leaned to compensate Computer voltage signals: Analog: Continuous and variable Voltages on a graph look like a wave Digital: Only has two voltage levels: on and off Only kind of signal the automotive computer understands Types of control modules: Engine control module (ECM) Powertrain control module (PCM) Vehicle control module (VCM) Components on the printed circuit board (PCB): Resistors Capacitors Integrated circuits: Clock circuit Microprocessor unit (MPU) or central processing unit (CPU) Other electronic components Random access memory (RAM): Non-permanent type of memory Stores temporary data Stored data is erased when PCM loses power (volatile memory) Read only memory (ROM): Data cannot be erased or changed Data can only be read Data written from factory is permanent Information randomly accessed from specific location Contains low level instructions to perform tasks of managing engine Does not need applied power to store data (non-volatile) Programmable read only memory (PROM): Can be randomly accessed Is non-volatile When manufactured, all memory locations are empty Electronically written for specific vehicles Many are socketed Electronically erasable programmable read only memory (EEPROM): Permanently soldered to PCM circuit boards Can be reprogrammed using Techline scan tool Serial data: String of information transmitted in sequence, one item at a time Consists of voltage signals changing from high to low (on to off) Each individual signal is known as a bit Series of 8 bits makes up a byte (word) Wires that carry serial data messages are called the data bus Serial data stream: Bits are transmitted at exact intervals Speed at which bits are transmitted is called the baud rate (bits per second) Early ECMs had baud rate of 160 Beginning in 1986 model year, ECMs had baud rate of 8,192 OBD II vehicles use data stream with baud rate of 10.4K (10,400 bits per second) Computer communications: Unidirectional - serial data is output only Bi-directional - serial data is both output and input Tech 1 and Tech 2 are bi-directional Universal asynchronous receive and transmit (UART): Used prior to OBD II 5-volt data line Toggles voltage at fixed bit pulse width Class 2 communication: Communicates between PCM, other control modules, and scan tool Toggles voltage from 0 to 7 volts Data can be transferred in short or long pulse widths DLC modes (12-pin only): Terminal B is supplied 5 volts by ECM In diagnostic mode ECM will: Display DTC 12 by flashing MIL Flash DTCs stored in memory (3 times each) Energize relays and solenoids Move IAC valve Field service mode: In Open Loop, MIL will flash 2.5 times per second In Closed Loop, MIL will: Flash once per second Stay off most of the time if system is running lean Stay on most of the time if system is running rich Fixed timing on some models Serial data may not be displayed Run timers are overridden Diagnostic (10K) mode: All attainable data is displayed Run timers are overridden Timing may be advanced if equipped with knock sensor system IAC is controlled to maintain fixed engine speed, usually 1000 RPM Park/Neutral restrict functions disabled EVAP purge solenoid may be enabled on some systems Important - Do NOT drive the vehicle in Field Service or 10K Mode. Timing may be affected and catalytic converter damage may occur. The road test (open) mode: Allows ECM to function normally Can be optional mode selection on systems that require diagnostic (10K) mode Allows only a few data parameters to display PCM in starting mode: Energizes fuel pump relay to pressurize fuel system Determines initial air/fuel ratio Delivers one injector pulse per RPM reference pulse Adjusts injector pulse width Coolant temperature rises, shortening pulse width (air/fuel ratio becomes leaner) PCM determines cranking mode air/fuel ratios (1.5:1 to 14.7:1) If throttle is open, air/fuel ratio changes Clear flood mode: Accelerator pedal pressed to floor (WOT) to assure 80% TP attained RPM below 600 PCM pulses injectors for 20:1 air/fuel ratio In some applications, PCM completely cuts off fuel PCM in open loop run mode: Does not use O2 sensor information to control air/fuel mixture Calculates ratio based on inputs from ECT, IAT, TP, MAP or MAF, and CKP sensors Remains in open loop until: O2 sensor warms up Coolant temperature reaches specific temperature Specified time has elapsed Closed loop run mode: O2 sensor warmed up Engine at specified temperature Predetermined time has elapsed Air/fuel is controlled to 14.7:1 based on O2 feedback Semi-closed loop mode: Highway driving, light engine load PCM corrects fuel leaner than 14.7:1 for improved fuel economy Converter protection mode: PCM determines converter overheat condition, returns to open loop Enriches air/fuel mixture to cool converter Acceleration enrichment mode: Simultaneous increase in TP and MAP PCM increases injector pulse width PCM provides additional pulses timed between base pulses Prevents engine stumble during hard acceleration Deceleration enleanment mode: Reduces emissions, prevents backfire Light throttle deceleration - PCM shortens injector on-time Close throttle deceleration - PCM may cut off fuel entirely Fuel cut-off mode: PCM shuts off fuel at predetermined MPH and RPM Fuel cut-off when ignition OFF Prevents dieseling or run-on Selective fuel cut-off mode: Used for engine torque management protection Used to reduce torque during transmission/transaxle shifts Used to reduce torque in conjunction with brakes applying Protects engine from overheating when coolant is low PCM runs engine with only RPM, TP and ECT inputs Limp-home mode Goes into backup if any of the following exist: Computer voltage below 9 vdc Cranking voltage below 9 vdc PROM missing or not functioning Circuits fail to issue computer operation pulses (COP) Battery voltage correction: Compensates for variations in battery voltage to fuel pump and injectors: PCM increases pulse width to injectors PCM increases idle RPM PCM increases dwell on EI systems Correction can occur in any operating mode Check mode: Enables PCM to detect engine control system malfunctions Can be requested by using Output Controls feature on scan tool PCM will turn on MIL and record freeze frame data Not all engine control diagnostics can be enhanced by check mode Can be performed while driving Refer to Service Information for detailed procedures PCM uses speed density to calculate mass air flow using: MAP Temperature RPM Estimates of volumetric efficiency EGR Mass air flow (MAF) sensor: Positioned in intake air duct or manifold Measures volume and density of incoming air: Temperature Density Humidity PCM reads actual mass air flow to calculate fuel requirements MAF sensor: Located before throttle plate in intake airflow Uses honeycell screen to break up incoming air turbulence Electronic sensing circuits are located in carrier assembly Uses resistive element that is heated above ambient temperature Theft deterrent fuel enable: Correct signal enables fuel injectors Incorrect signal disables fuel system Traction control desired torque request system: Constant communications between EBTCM and PCM Desired torque request ranges from 0% to 100% EBTCM reduces pulse width of traction control PCM reduces wheel slippage by one of the following: Retarding spark timing Closing throttle Decreasing boost solenoid PWM Disabling fuel injectors PCM controlled transmission/transaxle: Controls: Torque converter clutch apply solenoid Shift solenoids Downshift solenoids Pressure control solenoid Create improved shift timing and feel Idle learn procedure: Learned idle position is lost when: PCM or battery is disconnected PCM loses power PCM is reprogrammed Engine idle is unstable when learned idle position is lost Transmission shifting: PCM identifies if upshift is acceptable to analyze PCM compares actual shift time to desired shift time If actual shift time is long, PCM decreases current to PC solenoid If actual shift time is short, PCM increases current to PC solenoid Crankshaft variation learn procedure should be performed if any of the following conditions are true: DTC P1336 is set PCM has been replaced Engine has been replaced Crankshaft has been replaced Crankshaft harmonic balancer has been replaced Crankshaft position sensor has been replaced Crankshaft position system variation learn will be inhibited if: Engine coolant temperature less than 70° C (158° F) Any powertrain DTCs, other than DTC P1336, are set PCM detects malfunction involving: Camshaft position signal circuit 3X reference circuit 18X reference circuit PCM inputs: Switches Digital signals Variable sensors Switched inputs: Either high or low signal Pull-up circuit: Power source is outside PCM Closed switch generates high reference signal Open switch generates low reference signal Pull-down circuit: Receives reference voltage signal from PCM Closed switch signal, voltage pulled low to external ground Open switch, PCM registers high reference signal Digital input sensors: Use On/Off signal, similar to switch Switch On and Off rapidly PCM uses rate at which it switches as input signal Hall effect switch: No vane in switch transistor on and grounded Vane in switch transistor is off and signal is at high state Electronic device that produces voltage signal controlled by magnetic field Voltage passed through semiconductor wafer in Hall switch Permanent magnet induces Hall voltage across semiconductor Metal vane comes between magnet and semiconductor, interrupting magnetic field Pull-up Pull-down Refer to electrical schematics when performing diagnosis CKP (crank) Camshaft (CMP) position sensor: Identifies cylinder stroke PCM uses signal as sync pulse to trigger injectors in proper sequence PCM uses signal to indicate position of #1 piston during its intake stroke Synchronizes ignition system Calculates true sequential fuel injection (SFI) Vehicle speed sensor: PCM need information about vehicle speed to operate: Idle air control valve (IACV) Canister purge (EVAP) Torque converter clutch (TCC) Cruise control Transmission shift solenoids Electric cooling fans Magnetic VSS: Permanent magnet generator Mounted in the speedometer cable opening Produces AC voltage AC voltage converted to digital signals by VSS buffer The optical VSS is located inside the speedometer head. Its components include: Photocell LED Buffer circuit Spinning mirrored reflector E-85 configuration: Allows use of gasoline with up to 85% ethanol Provides alternative fuel capability Accomplished with addition of ethanol compatible components: Fuel pump Fuel lines Pressure regulator Fuel rail Fuel injectors Flexible fuel composition sensor (FCS) FCS: Three wire sensor with fuel inlet and outlet Measures fuel temperature and alcohol percentage Fuel composition sensor (FCS): Supplies PCM with alcohol content information Measures fuel temperature through internal thermistor Fuel conductivity and capacitance are electronically measured inside sensor Diagnostics check for frequency out of range or intermittent due to: Circuit faults Sensor issues Fuel contamination J-44175 fuel composition tester is used to diagnose fuel quality and sensor concerns Special fuel gauge necessary, has an orange face Manifold absolute pressure (MAP) sensor: Three wire sensor Located in engine compartment Measures changes in intake manifold air pressure PCM uses MAP readings to calculate: Fuel delivery Spark timing Barometric pressure reading (Baro) Fuel delivery calculations at start up Fuel and spark calculations during engine run Updated when ignition is turned on and when throttle is wide open Strain gauge MAP sensor: Contains 3 mm square silicon chip: Placed in sealed housing Connected to manifold Low manifold pressure causes sensor voltage to be low High manifold pressure causes sensor voltage to be high Mass air flow (MAF) sensor: Positioned in intake air duct or manifold Measures volume and density of incoming air Calculates actual mass air flow using: Temperature Density Humidity Resistance of conductor varies with temperature: Maintained at constant calibrated temperature Air current is required to maintain constant temperature Current translates into voltage signal sent to PCM Oxygen sensor (O2S): Able to generate its own low voltage signal Located in exhaust system Monitors amount of oxygen in exhaust stream One wire: Ground through pipe Two Wire It's own ground Heated oxygen sensor (HO2S): Three wire: One wire is the O2S signal One wire is the heater voltage One wire is the ground Four wire: Two signal wires (high and low) Two heater wires (power and ground) O2S construction: Center element made of zirconia Two platinum electrodes Inner surface: Exposed to outside air Forms positive terminal Outside surface: Coated with platinum Exposed to exhaust gases Forms negative terminal OS2 operation: PCM applies reference voltage of 450 millivolts PCM compares reference voltage with O2S voltage Rich air/fuel ratio: Exhaust contains almost no oxygen Air/fuel ratio below 14.7:1 O2S generates high voltage, above 450 millivolts Lean air/fuel ratio: Exhaust contains about 2% oxygen Air/fuel ratio above 14.7:1 O2S generates low voltage, below 450 millivolts O2S output voltage constantly fluctuates up and down and is used for: Adjusting injector operation Determining short-term and long-term fuel trim Open loop/closed loop criteria EGR diagnostics Monitoring catalyst efficiency Secondary air and EVAP diagnostics Throttle position (TP) sensor: Three-wire variable resistor Mounted to throttle body Closed throttle shows low voltage signal Open throttle shows high voltage signal PCM uses TP sensor information to calculate: Fuel delivery Ignition timing Transmission shifting schedule EGR Torque converter clutch (TCC) application Upshift light operation Evaporative emission (EVAP) control system Throttle position sensor: Relays exact position of throttle plate Adjustable: Slotted screw holes Crescent-shaped washers Non-adjustable: Round holes Washers Engine coolant temperature sensor (ECT): Two-wire sensor In direct contact with engine coolant Contains thermistor Cold temperatures provide high signal voltage Warm temperatures provide low signal voltage The PCM uses information about coolant temperatures to make the necessary calculations for the following operations: Fuel delivery Ignition control (IC) Knock sensor system Idle speed (IAC) Torque converter clutch application (TCC) Canister purge (EVAP) Exhaust gas recirculation (EGR) Cooling fan operation Intake air temperature sensor (IAT): Two-wire sensor Registers temperature of incoming air Thermistor device Resistance decreases as temperature increases PCM needs IAT readings to: Adjust air/fuel ratio in accordance with air density Modify spark advance and acceleration enrichment Determine when to enable EGR Fuel tank pressure sensor: Detects leaks in EVAP system Three-wire strain gauge sensor Measures difference in air pressure between fuel tank and outside air Mounts at top of fuel tank sending unit Knock sensor (KS): Controls ignition timing Detects engine detonation or knock Knock sensor operation: PCM supplies 5-volt reference signal to determine if circuit is: Open Shorted to ground Shorted to voltage KS sends PCM an AC voltage signal when detonation occurs: PCM modifies ignition timing to control knock When signal stops, PCM returns ignition timing to normal Knock sensor self-test mode: Occurs once per engine start-up Ignition is advanced to induce knock Bypassed if knock occurs and is detected before self-test begins Ceramic resistor card fuel level sensor: 40-250 ohm potentiometer Consists of: Ceramic card Wiper arm Float arm assembly Wire harness assembly Converts fuel tank level changes into variable electrical signals Attached to outside surface of modular fuel sender assembly Power received from PCM Accelerator pedal position (APP) sensor: Mounted on accelerator pedal assembly Works with TP sensor and TAC module Consists of three individual sensors: APP sensor 1 signal increases from below 1 volt to above 2 volts APP sensor 2 signal decreases from above 4 volts to below 2.9 volts APP sensor 3 signal decreases from above 3.8 volts to below 3.1 volts Park/neutral position switch may be located on: Steering column Console Transaxle in engine compartment PNP switch input is used by the PCM to control: Torque converter clutch (TCC) Spark timing Exhaust gas recirculation (EGR) VSS diagnostics Idle air control (IAC) Transmission range switch: Part of PNP and back-up lamp switch Externally mounted on trans manual shaft Multi-signal switch PCM supplies voltage to switch on four signal circuits: A, B, C, and P PCM compares voltage combinations on circuits to lookup table to determine gear range selected PCM detects selected gear by state of input Switch input represented as Hi and Low on scan tool Hi - ignition voltage signal Low - zero voltage signal Four transmission range parameters A, B, C, Parity Traction control desired torque request - PCM reduces wheel slippage by performing one or more of the following functions: Retarding spark timing Closing throttle Decreasing boost solenoid PWM Disabling fuel injectors Power steering pressure (PSP) switch: Two wire, on/off switch Located in power steering fluid pressure line Used to detect high system pressure PCM uses information from the PSP for: IAC control Spark retard during idle A/C compressor control Controller uses transmission gear switch information to identify: Commanded gear TCC apply Note: An electronic transmission or transaxle can be controlled by an ECM or PCM. The controller is identified as a PCM when it stores codes for the transmission or transaxle.