Engine Controls - 6.0L - Troubleshooting: Other Pontiac GTO IV

Intermittent Conditions

Intermittent Conditions

Hard Start

Hard Start

Surges/Chuggles

Surges/Chuggles

Lack of Power, Sluggishness, or Sponginess

Lack of Power, Sluggishness, or Sponginess

Detonation/Spark Knock

Detonation/Spark Knock

Hesitation, Sag, Stumble

Hesitation, Sag, Stumble

Cuts Out, Misses

Cuts Out, Misses

Poor Fuel Economy

Poor Fuel Economy

Poor Fuel Fill Quality

Poor Fuel Fill Quality

Rough, Unstable, or Incorrect Idle and Stalling

Rough, Unstable, or Incorrect Idle and Stalling

Dieseling, Run-On

Dieseling, Run-On

Backfire

Backfire

Conditions for Updating the I/M System Status

Each system monitor requires at least one, and sometimes several diagnostic tests. The result of each test is reported by a diagnostic trouble code (DTC). A system monitor is complete when either all of the DTCs comprising the monitor have Run and Passed, or when any one of the DTCs comprising the monitor has illuminated the malfunction indicator lamp (MIL). Once the system monitor is complete, the I/M System Status display will indicate YES in the Completed column.

For example, when the HO2S Heater Status indicates YES, either all of the oxygen sensor heater tests have passed or one of the tests has illuminated the MIL. If the vehicle has four heated oxygen sensors, either all four heater circuit tests have passed or one of the heater circuit tests has illuminated the MIL. The I/M System Status will indicate NO under the Completed column when any of the required tests for that system have not run. The following is a list of conditions that would set the I/M System Status indicator to NO

1. The vehicle is new from the factory and has not yet been driven through the necessary drive conditions to complete the tests.
2. The battery has been disconnected or discharged below operating voltage.
3. The control module power or ground has been interrupted.
4. The control module has been reprogrammed.
5. The control module DTCs have been cleared.

Monitored Emission Control Systems

The OBD II System monitors all emission control systems that are on-board. Not all vehicles have a full complement of emission control systems. For example, a vehicle may not be equipped with secondary air injection (AIR) or exhaust gas recirculation (EGR). The OBD II regulations require monitoring of the following

1. The air conditioning system
2. The catalytic converter efficiency
3. Comprehensive component monitoring-Emission related inputs and outputs
4. The evaporative emissions (EVAP) system
5. The EGR System
6. The fuel delivery system
7. Heated catalyst monitoring
8. Misfire monitoring
9. The oxygen sensor system (O2S or HO2S)
10. The oxygen sensor heater system (HO2S heater)
11. The AIR system

For the specific DTCs required for each system, refer to Inspection/Maintenance (I/M) System DTC Table . Systems such as fuel delivery, misfire, and comprehensive components may not be listed in a system status list. These tests run continuously and do not require an I/M System Status indicator.

Inspection/Maintenance (I/M) System Check

CKP System Variation Learn Procedure

1. Install a scan tool.
2. Monitor the engine control module (ECM) for DTCs with a scan tool. If other DTCs are set, except DTC P0315, refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(ref-201037-S01449858442005102400000) in Vehicle DTC Information for the applicable DTC that set.
3. Select the crankshaft position (CKP) variation learn procedure with a scan tool.
4. The scan tool instructs you to perform the following: Accelerate to wide open throttle (WOT). Release throttle when fuel cut-off occurs. Observe fuel cut-off for applicable engine. Engine should not accelerate beyond calibrated RPM value. Release throttle immediately if value is exceeded. Block drive wheels. Set parking brake. DO NOT apply brake pedal. Cycle ignition from OFF to ON. Apply and hold brake pedal. Start and idle engine. Turn A/C OFF. Vehicle must remain in Park or Neutral. The scan tool monitors certain component signals to determine if all the conditions are met to continue with the procedure. The scan tool only displays the condition that inhibits the procedure. The scan tool monitors the following components: CKP sensors activity-If there is a CKP sensor condition, refer to the applicable DTC that set. Camshaft position (CMP) sensor activity-If there is a CMP sensor condition, refer to the applicable DTC that set. Engine coolant temperature (ECT)-If the ECT is not warm enough, idle the engine until the engine coolant temperature reaches the correct temperature.
5. Enable the CKP system variation learn procedure with a scan tool.
6. Accelerate to WOT.
7. Release when the fuel cut-off occurs.
8. Test in progress
9. The scan tool displays Learn Status: Learned this ignition. If the scan tool indicates that DTC P0315 ran and passed, the CKP variation learn procedure is complete. If the scan tool indicates DTC P0315 failed or did not run, refer to «DTC P0315»(ref-201093-S09750374382005102400000) . If any other DTCs set, refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(ref-201037-S01449858442005102400000) in Vehicle DTC Information for the applicable DTC that set.
10. Turn OFF the ignition for 30 seconds after the learn procedure is completed successfully.
11. The CKP system variation learn procedure is also required when the following service procedures have been performed, regardless of whether DTC P0315 is set: A CKP sensor replacement An engine replacement An ECM replacement A harmonic balancer replacement A crankshaft replacement Any engine repairs which disturb the CKP sensor relationship

Throttle Body Cleaning Procedure

1. Remove the air intake duct. Refer to «Air Cleaner Assembly Replacement»(ref-201043-S28051882602005102400000) . NOTE: Do not insert any tools into the throttle body bore in order to avoid damage to the throttle valve plate.
2. Inspect the throttle body bore and inspect the throttle valve plate for deposits. The throttle valve must be opened in order to inspect all surfaces. NOTE: Do not use any solvent that contains Methyl Ethyl Ketone (MEK). This solvent may damage fuel system components.
3. Clean the throttle body bore and the throttle valve plate using a clean shop towel with GM Top Engine Cleaner, P/N 1052626 (Canadian P/N 993026).
4. Install the air intake duct. Refer to «Air Cleaner Assembly Replacement»(ref-201043-S28051882602005102400000) .

Tool Required

J 34730-1A Fuel Pressure Gage. See Special Tools .

1. Turn OFF the ignition. CAUTION: Refer to the Battery Disconnect Caution in Cautions and Notices.
2. Disconnect the negative battery cable in order to avoid possible fuel discharge if an accidental attempt is made to start the engine.
3. Loosen the fuel filler cap in order to relieve the fuel tank vapor pressure.
4. Remove the left fuel rail cover.
5. Connect the J 34730-1A fuel pressure gage to the fuel pressure connection. See «Special Tools»(ref-201043-S19962986522005102400000) . Wrap a shop towel around the fitting while connecting the gage in order to avoid spillage.
6. Install the bleed hose of the gage into an approved container.
7. Open the valve on the gage to bleed the system pressure. The fuel connections are now safe for servicing.
8. Drain any fuel remaining in the gage into an approved container.

Tools Required

1. EN-46843 Tool Set, Quick Connect Fitting Release Tool. See «Special Tools»(ref-201043-S19962986522005102400000) .
2. J 37088-A Tool Set, Fuel Line Quick Connect Separator. See «Special Tools»(ref-201043-S19962986522005102400000) .

1. EN-46843 Tool Set, Quick Connect Fitting Release Tool. See «Special Tools»(ref-201043-S19962986522005102400000) .
2. J 37088-A Tool Set, Fuel Line Quick Connect Separator. See «Special Tools»(ref-201043-S19962986522005102400000) .

1. J 45004 Fuel Tank Drain Hose. See «Special Tools»(ref-201043-S19962986522005102400000) .
2. J 42960-2 Fuel Flapper Door Holder. See «Special Tools»(ref-201043-S19962986522005102400000) .

J 45722 Fuel Sender Lock Ring Wrench. See Special Tools .

1. J 34730-1A Fuel Pressure Gage. See «Special Tools»(ref-201043-S19962986522005102400000) .
2. J 45722 Fuel Sender Lock Ring Wrench. See «Special Tools»(ref-201043-S19962986522005102400000) .
3. J 45004 Fuel Tank Drain Hose. See «Special Tools»(ref-201043-S19962986522005102400000) .
4. J 42960-2 Fuel Flapper Door Holder. See «Special Tools»(ref-201043-S19962986522005102400000) .

Cleaning Procedure

1. Disconnect the negative battery cable.
2. Relieve the fuel system pressure. Refer to the «Fuel Pressure Relief Procedure»(ref-201043-S21654027382005102400000) .
3. Drain the fuel tank. Refer to «Fuel Tank Draining Procedure»(ref-201043-S41971780112005102400000) .
4. Remove the fuel tank. Refer to «Fuel Tank Replacement»(ref-201043-S37798638172005102400000) .
5. Remove the fuel sender assembly. Refer to «Fuel Sender Assembly Replacement»(ref-201043-S26183717232005102400000) .
6. Inspect the fuel pump strainer. Replace a contaminated strainer and inspect the fuel pump.
7. Inspect the fuel pump inlet for dirt and debris. Replace the fuel pump if you find dirt or debris in the fuel pump inlet.
8. Flush the fuel tank with hot water.
9. Pour the water out of the fuel sender assembly opening. Rock the tank to ensure that all water is removed from the tank.
10. Install the fuel sender assembly. Refer to «Fuel Sender Assembly Replacement»(ref-201043-S26183717232005102400000) .
11. Install the fuel tank. Refer to «Fuel Tank Replacement»(ref-201043-S37798638172005102400000) .
12. Refill the fuel tank.
13. Install the fuel filler cap.
14. Connect the negative battery cable.
15. Inspect for leaks. Turn ON the ignition for 2 seconds. Turn OFF the ignition for 10 seconds. Turn ON the ignition. Inspect for fuel leaks.

Scheme 29

Note the location of the fuel rail ground strap (557).

1. Relieve the fuel system pressure. Refer to the «Fuel Pressure Relief Procedure»(ref-201043-S21654027382005102400000) .
2. Before removal, clean the fuel rail assembly with a spray type engine cleaner, GM X-30A or equivalent, if necessary. Follow the package instructions. Do not soak fuel rails in liquid cleaning solvent.
3. Disconnect the fuel feed hose from the fuel rail. Refer to «Quick Connect Fitting(s) Service (Metal Collar)»(ref-201043-S03534227022005102400000) .
4. Disconnect the electrical connectors from the fuel injectors. Identify the connectors to their corresponding injectors to ensure correct sequential injector firing order after reassembly.
5. Disconnect the electrical harness from the fuel rail brackets.
6. Remove the fuel rail attaching bolts (511, 512), ground strap (557).
7. Lift evenly on both sides of the fuel rail, and remove the fuel rail assembly.
8. Remove the injector lower O-ring seal from the spray tip end of each injector.
9. Discard the O-ring seals.

1. J 37287 Fuel Line Shut-Off Adapters. See «Special Tools»(ref-201043-S19962986522005102400000) .
2. J 35800-A Fuel Injector Cleaner
3. J 42873-1 3/8 Fuel Line Shut-Off Valve
4. J 42873-2 5/16 Return Pipe Shut-Off Valve
5. J 42964-1 3/8 Fuel Pipe Shut-Off Valve
6. J 42964-2 5/16 Fuel Pipe Shut-Off Valve

Note. GM Top-Engine Cleaner is the only injector cleaning agent recommended. Do not use other cleaning agents, as they may contain methanol which can damage fuel system components. Under NO circumstances should the top engine cleaner be added to the vehicles fuel tank, as it may damage the fuel pump and other system components. Do not exceed a 10 percent cleaning solution concentration. Higher concentrations may damage fuel system components. Testing has demonstrated that exceeding the 10 percent cleaning solution concentration does not improve the effectiveness of this procedure.

Fuel Injector Cleaning Procedure

1. Obtain J 35800-A (2).
2. For US dealers, empty 2 pre-measured GM Top-Engine Cleaner containers, 24 ml (0.812 oz.) each, GM P/N 12346535, into the J 35800-A .
3. For Canadian dealers, measure and dispense 48 ml (1.62 oz.) of Top-Engine Cleaner, Canadian P/N 992872, into the J 35800-A .
4. If you are using any other brand of tank you will need a total of 96 ml (3.24 oz.) of Top-Engine Cleaner mixed with 864 ml (29.16 oz.) of regular unleaded gasoline.
5. Fill the injector cleaning tank with regular unleaded gasoline. Be sure to follow all additional instructions provided with the tool.
6. Electrically disable the vehicle fuel pump by removing the fuel pump relay and disconnecting the oil pressure switch connector, if equipped.
7. Disconnect the fuel feed and return line, if equipped, at the fuel rail. Plug the fuel feed and return line, if equipped, coming off the fuel rail with J 37287 , or J 42964-1 and J 42964-2 or J 42873-1 and J 42873-2 as appropriate for the fuel system.
8. Connect the J 35800-A to the vehicle fuel rail.
9. Pressurize the J 35800-A to 510 kPa (75 psi).
10. Start and idle the engine until it stalls due to lack of fuel. This should take approximately 15-20 minutes.
11. Disconnect J 35800-A from the fuel rail.
12. Reconnect the vehicle fuel pump relay and oil pressure switch connector, if equipped.
13. Remove J 37287 or J 42964-1 and J 42964-2 or J 42873-1 and J 42873-2 and reconnect the vehicle fuel feed and return lines.
14. Start and idle the vehicle for an additional 2 minutes to ensure residual injector cleaner is flushed from the fuel rail and fuel lines.
15. Repeat steps 1-5 of the Injector Balance Test, and record the fuel pressure drop from each injector.
16. Subtract the lowest fuel pressure drop from the highest fuel pressure drop. If the value is 15 kPa (2 psi) or less, no additional action is required. If the value is greater than 15 kPa (2 psi), replace the injector with the lowest fuel pressure drop.
17. Add one ounce of Port Fuel Injector Cleaner, GM P/N 12345104 (Canadian P/N 10953467), to the vehicle fuel tank for each gallon of gasoline estimated to be in the fuel tank. Instruct the customer to add the reminder of the bottle of Port Fuel Injector Cleaner to the vehicle fuel tank at the next fill-up.
18. Advise the customer to change brands of fuel and to add GM Port Fuel Injector Cleaner every 5 000 km (3,000 mi). GM Port Fuel Injector Cleaner contains the same additives that the fuel companies are removing from the fuel to reduce costs. Regular use of GM Port Fuel Injector Cleaner should keep the customer from having to repeat the injector cleaning procedure.
19. Road test the vehicle to verify that the customer concern has been corrected.

1. J 34730-1A Fuel Pressure Gage. See «Special Tools»(ref-201043-S19962986522005102400000) .
2. J 37088-A Tool Set, Fuel Line Quick Connect Separator. See «Special Tools»(ref-201043-S19962986522005102400000) .

Spark Plug Usage

1. Ensure that the correct spark plug is installed. An incorrect spark plug causes poor driveability conditions. Refer to «Ignition System Specifications»(ref-201087-S28844541212005102400000) for the correct spark plug.
2. Ensure that the spark plug has the correct heat range. An incorrect heat range causes the following conditions: Spark plug fouling due to a colder plug A pre-ignition condition, causing spark plug and/or engine damage due to a hotter plug

Purpose

The Throttle Actuator Control (TAC) system delivers improved throttle response and greater reliability and eliminates the need for mechanical cable. The TAC system performs the following functions

1. Accelerator pedal position sensing
2. Throttle positioning to meet driver and engine demands
3. Throttle position sensing
4. Internal diagnostics
5. Cruise control functions
6. Manage TAC electrical power consumption

The TAC system includes the following components

1. The accelerator pedal position (APP) sensors
2. The throttle body assembly
3. The engine control module (ECM)

Accelerator Pedal Position (APP) Sensor

The accelerator pedal contains 2 individual Accelerator Pedal Position (APP) sensors within the assembly. The APP sensors 1 and 2 are potentiometer type sensors each with 3 circuits

1. A 5-volt reference circuit
2. A low reference circuit
3. A signal circuit

The APP sensors are used to determine the pedal angle. The engine control module (ECM) provides each APP sensor a 5-volt reference circuit and a low reference circuit. The APP sensors provide the ECM with signal voltage proportional to the pedal movement. The APP sensor 1 signal voltage at rest position is less than 1 volt and increases as the pedal is actuated. The APP sensor 2 signal voltage at rest position above 4 volts and decreases as the pedal is actuated.

Engine Control Module

The Engine Control Module (ECM) is the control center for the throttle actuator control (TAC) system. The ECM determines the drivers intent and then calculates the appropriate throttle response. The ECM achieves throttle positioning by providing a pulse width modulated voltage to the TAC motor.

Normal Mode

During the operation of the throttle actuator control (TAC) system, several modes or functions are considered normal. The following modes may be entered during normal operation

1. Minimum pedal value-At key-up, the engine control module (ECM) updates the learned minimum pedal value.
2. Minimum throttle position (TP) values-At key-up, the ECM updates the learned minimum TP value. In order to learn the minimum TP value, the throttle blade is moved to the closed position.
3. Ice break mode-If the throttle is not able to reach a predetermined minimum throttle position, the ice break mode is entered. During the ice break mode, the ECM commands the maximum pulse width several times to the throttle actuator motor in the closing direction.
4. Battery saver mode-After a predetermined time without engine RPM, the ECM commands the battery saver mode. During the battery saver mode, the TAC module removes the voltage from the motor control circuits, which removes the current draw used to maintain the idle position and allows the throttle to return to the spring loaded default position.

Reduced Engine Power Mode

When the ECM detects a condition with the TAC system, the ECM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions

1. Acceleration limiting-The ECM will continue to use the accelerator pedal for throttle control, however, the vehicle acceleration is limited.
2. Limited throttle mode-The ECM will continue to use the accelerator pedal for throttle control, however, the maximum throttle opening is limited.
3. Throttle default mode-The ECM will turn OFF the throttle actuator motor and the throttle will return to the spring loaded default position.
4. Forced idle mode-The ECM will perform the following actions: Limit engine speed to idle by positioning the throttle position, or by controlling the fuel and spark if the throttle is turned OFF. Ignore the accelerator pedal input.
5. Engine shutdown mode-The ECM will disable fuel and de-energize the throttle actuator.

Fuel Tank Filler Pipe

The fuel tank filler pipe has a built-in restrictor and deflector in order to prevent refueling with leaded fuel.

Scheme 30

Note. If a fuel tank filler cap requires replacement, use only a fuel tank filler cap with the same features. Failure to use the correct fuel tank filler cap can result in a serious malfunction of the fuel and EVAP system.

The fuel filler cap (3) is a screw-on type, with an integrated tightening torque limiting mechanism. When installing the cap, tighten it until a ratcheting (clicking) sound is heard, indicating the cap is properly tightened. The fuel tank filler cap is tethered to the fuel filler pocket. The fuel tank filler cap requires a quarter of a turn in order to be removed.

Scheme 31

An in-tank modular fuel pump and sender assembly is attached from the top of the fuel tank and incorporates a modular fuel pump assembly, a fuel strainer and fuel filter, a reservoir, fuel level sender assembly, pressure regulator and reservoir jet pump. A fuel Fill Limiter Vent Valve (FLVV) and fuel tank pressure sensor is incorporated into the modular fuel pump and sender cover assembly.

Fuel Pump

The fuel pump is incorporated into the design of the modular fuel sender assembly inside the fuel tank and is an electric, high pressure, single turbine design. The fuel pump provides fuel to the fuel rail assembly at a specified flow and pressure. The fuel pump delivers a constant flow of fuel to the engine, even during low fuel conditions or aggressive vehicle maneuvers. The engine control module (ECM) controls the electric fuel pump operation through the fuel pump relay.

Fuel Pump Strainer

The fuel strainer connects onto the fuel pump inlet port on the end cap of the fuel pump assembly and consists of a finely woven plastic filter. A metal compression ring is fitted around the plastic strainer to fuel pump feed port and the complete fuel strainer assembly is fastened to the fuel pump end cap with a metal speed clip fastener. The strainers function is to filter fuel contaminants from within the fuel reservoir and also act to wick the fuel. The fuel strainer is serviced as part of the complete fuel pump and strainer assembly. Fuel stoppage at the strainer indicates an abnormal amount of sediment in the fuel tank which should be removed before reinstallation of the fuel tank into the vehicle.

Nylon Fuel Pipes

Nylon fuel pipes are designed to perform the same job as the steel or flexible fuel pipes or hoses that they replace. Nylon pipes are constructed to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There are 3 sizes of nylon pipes used: 3/8 in ID for the fuel feed, 5/16 in ID for the fuel return, and 1/2 in ID for the vent. Heat-resistant rubber hose and/or corrugated plastic conduit protect the sections of the pipes that are exposed to chafing, to high temperature, or to vibration.

Nylon fuel pipes are somewhat flexible and can be formed around gradual turns under the vehicle. However, if nylon fuel pipes are forced into sharp bends, the pipes will kink and restrict the fuel flow. Once exposed to fuel, nylon pipes may become stiffer and are more likely to kink if the pipes are bent too far. Take special care when working on a vehicle with nylon fuel pipes.

Quick-Connect Fittings

Quick-connect fittings provide a simplified means of installing and connecting fuel system components. The fittings consist of a unique female connector and a compatible male pipe end. O-rings, located inside the female connector, provide the fuel seal. Integral locking tabs or fingers hold the fittings together.

Fuel Pipe O-Rings

O-rings seal the threaded connections in the fuel system. The fuel system O-ring seals are made of a special material. Service the O-ring seals with the correct service part.

EVAP Pipes and Hoses

The evaporative emission (EVAP) pipes extend from the fuel sender assembly and the EVAP canister vent solenoid to the EVAP canister. These pipes are located on top of the fuel tank. The EVAP purge pipe extends from the EVAP canister on top of the fuel tank to the EVAP purge solenoid in the engine compartment. The rear pipes and the engine compartment pipe are constructed of nylon. The chassis EVAP purge pipe is constructed of steel. The EVAP canister vent solenoid connects to the EVAP canister with a section of rubber hose.

Scheme 32

The enhanced evaporative emission (EVAP) service port is located in the EVAP pipe in the engine compartment near the purge solenoid. The service port is identified by a green cap. The port contains a Schrader valve and a fitting in order to allow the connection of the J 41413-200 Evaporative Emissions System Tester (EEST) for diagnosis of the evaporative emission system. See Special Tools .

On-Board Refueling Vapor Recovery System (ORVR)

The On-Board Refueling Vapor Recovery system (ORVR) is an on-board vehicle system that is designed to recover the fuel vapors during the vehicle refueling operation. The flow of liquid fuel down the fuel filler pipe provides a liquid seal, which prevents the vapor from leaving the fuel filler pipe. An evaporative emission (EVAP) pipe transports the fuel vapor to the EVAP canister for use by the engine. Listed below are the ORVR system components with a brief description of their operation

1. The EVAP canister. The EVAP canister receives refueling vapor from the fuel system, stores the vapor and releases the vapor to the engine upon demand.
2. The EVAP pipes. The EVAP pipes transport the fuel vapor from the fuel tank to the EVAP canister.
3. The fuel filler pipe. The fuel filler pipe carries the fuel from the fuel nozzle to the fuel tank.
4. The check valve. The check valve limits fuel spit back from the fuel tank during the refueling operation by allowing the fuel flow only into the fuel tank. This check valve is located at the bottom of the fuel filler pipe.
5. The modular fuel sender assembly. The assembly pumps the fuel to the engine from the fuel tank.
6. The Fill Limiter Vent Valve (FLVV). This valve acts as a shut-off valve. The FLVV is located at the top of the fuel sender assembly. This valve is not serviced separately. The FLVV has the following functions: The FLW controls the fuel tank fill level by closing the primary vent from the fuel tank. The FLW prevents the fuel from exiting the fuel tank via the EVAP pipe to the canister. The FLW provides fuel-spillage protection in the event of a vehicle rollover by closing the vapor path from the tank to the EVAP canister.

Starting Mode

With the ignition ON, before engaging the starter, the engine control module (ECM) energizes the fuel pump relay for two seconds allowing the fuel pump to build up pressure. The ECM first checks speed density, then switches to the mass air flow (MAF) sensor. The ECM also uses the engine coolant temperature (ECT), throttle position (TP), and manifold absolute pressure (MAP) sensors to determine the proper air/fuel ratio for starting. This ranges from 1.5:1 at -36°C (-33°F) to 14.7:1 at +94°C (+201°F) running temperature. The ECM controls the amount of fuel delivered in the starting mode by changing the pulse width of the injectors. This is done by pulsing the injectors for very short times.

Clear Flood Mode

If the engine floods, clear the engine by pushing the accelerator pedal down all the way. The engine control module (ECM) then pulses the injectors at an air/fuel ratio of 20:1. The ECM holds this injector rate as long as the throttle stays wide open and the engine speed is below 300 RPM. If the throttle position becomes less than 80 percent, the ECM returns to the starting mode.

Run Mode

The run mode has two conditions called Open Loop and Closed Loop. When the engine is first started, and engine speed is above a predetermined RPM, the system begins Open Loop operation. The engine control module (ECM) ignores the signal from the Heated Oxygen Sensor (HO2S) and calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT), Mass Air Flow (MAF), Manifold Absolute Pressure (MAP), and Throttle Position (TP) sensors. The system stays in Open Loop until meeting the following conditions

1. Both HO2S have varying voltage output, showing that they are hot enough to operate properly. This depends on temperature.
2. The ECT sensor is above a specified temperature.
3. A specific amount of time has elapsed after starting the engine.

Specific values for the above conditions exist for each different engine, and are stored in the electrically erasable programmable read only memory (EEPROM). The system begins Closed Loop operation after reaching these values. In Closed Loop, the ECM calculates the air/fuel ratio (injector on-time) based on the signal from various sensors, but mainly the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1.

Acceleration Mode

When the driver pushes on the accelerator pedal, air flow into the cylinders increases rapidly, while fuel flow tends to lag behind. To prevent possible hesitation, the Engine Control Module (ECM) increases the pulse width to the injectors to provide extra fuel during acceleration. The ECM determines the amount of fuel required based on throttle position, coolant temperature, manifold air pressure, mass air flow and engine speed.

Deceleration Mode

When the driver releases the accelerator pedal, air flow into the engine is reduced. The Engine Control Module (ECM) looks at the corresponding changes in throttle position, manifold air pressure and mass air flow. The ECM shuts OFF fuel completely if the deceleration is very rapid, or for long periods, such as long closed throttle coast-down. The fuel shuts OFF in order to protect the warm-up three-way catalytic converters.

Battery Voltage Correction Mode

When battery voltage is low, the Engine Control Module (ECM) compensates for the weak spark delivered by the ignition system in the following ways

1. Increasing the amount of fuel delivered
2. Increasing the idle RPM
3. Increasing ignition dwell time

Fuel Cutoff Mode

The Engine Control Module (ECM) cuts OFF fuel from the fuel injectors when the following conditions are met in order to protect the powertrain from damage and improve driveability

1. The ignition is OFF. This prevents engine run-on.
2. The ignition is ON, but there is no ignition reference signal. This prevents flooding or backfiring.
3. The engine speed is too high, above the red line.
4. The vehicle speed is too high, above rated tire speed.
5. During an extended, high speed, closed throttle coast down, this reduces emissions and increases engine braking.
6. During extended deceleration, in order to prevent damage to the catalytic converters.

Fuel Trim

The Engine Control Module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. The ECM monitors the heated oxygen sensor (HO2S) signal voltage while in Closed Loop and regulates the fuel delivery by adjusting the pulse width of the fuel injectors based on this signal. The ideal fuel trim values are around 0 percent for both short term and long term fuel trim. A positive fuel trim value indicates the ECM is adding fuel in order to compensate for a lean condition by increasing the pulse width. A negative fuel trim value indicates that the ECM is reducing the amount of fuel in order to compensate for a rich condition by decreasing the pulse width. A change made to the fuel delivery changes the short term and long term fuel trim values. The short term fuel trim values change rapidly in response to the HO2S signal voltage. These changes fine tune the engine fueling. The long term fuel trim makes coarse adjustments to the fueling in order to re-center and restore control to short term fuel trim. A scan tool can be used to monitor the short term and long term fuel trim values. The long term fuel trim diagnostic is based on an average of several of the long term speed load learn cells. The ECM selects the cells based on the engine speed and engine load. If the ECM detects an excessive lean or rich condition, the ECM will set a fuel trim DTC.

Fuel Pump Electrical Circuit

When the ignition switch is in the ON position, before engaging the starter, the engine control module (ECM) energizes the fuel pump relay for 2 seconds, causing the fuel pump to pressurize the fuel system. If the ECM does not receive ignition reference pulses with the engine cranking or running within 2 seconds, the ECM shuts OFF the fuel pump relay, causing the fuel pump to stop.

Scheme 33

The fuel rail assembly attaches to the engine intake manifold. The fuel rail assembly performs the following functions

1. Positions the injectors (3) in the intake manifold
2. Distributes fuel evenly to the injectors (2)
3. Fuel Raid Feed Pipe (1)

Fuel Injectors

The top-feed fuel injector assembly is a solenoid-operated device, controlled by the engine control module (ECM), that meters pressurized fuel to a single engine cylinder. The ECM energizes the injector solenoid, which opens a ball valve, allowing the fuel to flow past the ball valve, and through a recessed flow director plate. The director plate has multiple machined holes that control the fuel flow, generating a conical spray pattern of finely atomized fuel at the injector tip. Fuel is directed at the intake valve, causing the fuel to become further atomized and vaporized before entering the combustion chamber. An injector that is stuck partly open can cause a loss of pressure after the engine shutdown. Consequently, long cranking times would be noticed on some engines.

EVAP System Components

The evaporative emission (EVAP) system consists of the following components

EVAP Canister

The canister is filled with carbon pellets used to absorb and store fuel vapors. Fuel vapor is stored in the canister until the control module determines that the vapor can be consumed in the normal combustion process.

EVAP Purge Solenoid

The evaporative emission (EVAP) purge solenoid controls the flow of vapors from the EVAP system to the intake manifold. This normally closed solenoid is Pulse Width Modulated (PWM) by the control module to precisely control the flow of fuel vapor to the engine. The solenoid will also be opened during some portions of the EVAP testing, allowing engine vacuum to enter the EVAP system.

EVAP Vent Solenoid

The evaporative emission (EVAP) vent solenoid controls fresh airflow into the EVAP canister. The solenoid is normally open. The control module will command the solenoid closed during some EVAP tests, allowing the system to be tested for leaks.

Fuel Tank Pressure Sensor

The Fuel Tank Pressure (FTP) sensor measures the difference between the pressure or vacuum in the fuel tank and outside air pressure. The control module provides a 5-volt reference and a ground to the FTP sensor. The FTP sensor provides a signal voltage back to the control module that can vary between 0.1-4.9 volts. As FTP increases, FTP sensor voltage decreases, high pressure = low voltage. As FTP decreases, FTP voltage increases, low pressure or vacuum = high voltage.

EVAP Service Port

The evaporative emission (EVAP) service port is located in the EVAP purge pipe between the EVAP purge solenoid and the EVAP canister. The service port is identified by a green colored cap.

Crankshaft Position (CKP) Sensor

The Crankshaft Position (CKP) sensor is a three wire sensor based on the magneto resistive principle. A magneto resistive sensor uses two magnetic pickups between a permanent magnet. As an element such as a reluctor wheel passes the magnets the resulting change in the magnetic field is used by the sensor electronics to produce a digital output pulse. The Engine Control Module (ECM) supplies a 12-volt, low reference, and signal circuit to the CKP sensor. The sensor returns a digital ON/OFF pulse 24 times per crankshaft revolution.

Crankshaft Reluctor Wheel

The crankshaft reluctor wheel is mounted on the rear of the crankshaft. The wheel is comprised of four 90 degree segments. Each segment represents a pair of cylinders at Top Dead Center (TDC), and is further divided into six 15 degree segments. Within each 15 degree segment is a notch of 1 of 2 different sizes. Each 90 degree segment has a unique pattern of notches. This is known as pulse width encoding. This pulse width encoded pattern allows the engine control module (ECM) to quickly recognize which pair of cylinders are at TDC. The reluctor wheel is also a dual track-or mirror image-design. This means there is an additional wheel pressed against the first, with a gap of equal size to each notch of the mating wheel. When one sensing element of the crankshaft position (CKP) sensor is reading a notch, the other is reading a set of teeth. The resulting signals are then converted into a digital square wave output by the circuitry within the CKP sensor.

Camshaft Position (CMP) Sensor

The Camshaft Position (CMP) sensor is also a magneto resistive sensor, with the same type of circuits as the crankshaft position (CKP) sensor. The CMP sensor signal is a digital ON/OFF pulse, output once per revolution of the camshaft. The CMP sensor information is used by the engine control module (ECM) to determine the position of the valve train relative to the CKP.

Camshaft Reluctor Wheel

The camshaft reluctor wheel is either pressed onto the camshaft or part of the camshaft gear depending on the application. The feature-or target- is read in a radial or axial fashion respectively. The wheel is a smooth track, half of which is of a lower profile than the other half. This feature allows the camshaft position (CMP) sensor to supply a signal as soon as the key is turned ON, since the CMP sensor reads the track profile, instead of a notch.

Ignition Coils

Each ignition coil has an ignition 1 voltage feed and a ground. The Engine Control Module (ECM) supplies a low reference and an ignition control (IC) circuit. Each ignition coil contains a solid state driver module. The ECM will command the IC circuit ON, this allows the current to flow through the primary coil windings for the appropriate time or dwell. When the ECM commands the IC circuit OFF, this will interrupt current flow through the primary coil windings. The magnetic field created by the primary coil windings will collapse across the secondary coil windings, which induces a high voltage across the spark plug electrodes. The coils are current limited to prevent overloading if the IC current is held high too long. The spark plugs are connected to their respective coils by a short secondary wire. The spark plugs are tipped with iridium for long life and efficiency.

Engine Control Module (ECM)

The Engine Control Module (ECM) controls all ignition system functions, and constantly corrects the basic spark timing. The ECM monitors information from various sensor inputs that include the following

1. The throttle position (TP) sensor
2. The engine coolant temperature (ECT) sensor
3. The mass air flow (MAF) sensor
4. The intake air temperature (IAT) sensor
5. The vehicle speed sensor (VSS)
6. The transmission gear position or range information sensors
7. The engine knock sensors (KS)

The Knock Sensor (KS) system enables the control module to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The control module uses the KS system to test for abnormal engine noise that may indicate detonation, also known as spark knock.