Engine Controls - 8.1L (Introduction): Other Chevrolet Silverado 3500

Temperature vs Resistance

Temperature vs Resistance

Altitude vs Barometric Pressure

Altitude vs Barometric Pressure

CKP System Variation Learn Procedure

1. Install a scan tool.
2. Monitor the powertrain control module (PCM) for DTCs with a scan tool. If other DTCs are set, except DTC P0315, refer to «Diagnostic Trouble Code (DTC) List»(ref-184135-S26552404012005082200000) for the applicable DTC.
3. Select the crankshaft position 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 the 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: Crankshaft position (CKP) sensors activity-If there is a CKP sensor condition, refer to the applicable DTC. Camshaft position (CMP) signal activity-If there is a CMP signal condition, refer to the applicable DTC. Engine coolant temperature (ECT)-If the engine coolant temperature 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 the scan tool.
6. Accelerate to WOT.
7. Release throttle when fuel cut-off occurs.
8. The scan tool display reads 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-184253-S28846503152005082200000) . If any other DTCs set, refer to «Diagnostic Trouble Code (DTC) List»(ref-184135-S26552404012005082200000) for the applicable DTC.
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 or not DTC P0315 is set: An engine replacement A PCM replacement A harmonic balancer replacement A crankshaft replacement A CKP sensor replacement Any engine repairs which disturb the crankshaft to CKP sensor relationship.

Throttle Body Cleaning Procedure

1. Remove the intake air resonator. Refer to «Intake Air Resonator Replacement»(ref-184137-S05331089022005082200000) .
2. Inspect the throttle body bore and the throttle body plate for deposits. You will need to open the throttle plate in order to inspect all surfaces.
3. Clean the throttle body bore and the throttle plate using a clean shop towel with GM top engine cleaner, P/N 1052626 or AC Delco Carburetor Tune-up Conditioner, P/N X66P, or equivalent product.
4. Install the intake air resonator. Refer to «Intake Air Resonator Replacement»(ref-184137-S05331089022005082200000) .

Fuel Pressure Relief Procedure

Tools Required

J 34730-1A Fuel Pressure Gage

Scheme 219

1. Disconnect the negative battery cable. Refer to «Battery Negative Cable Disconnect/Connect Procedure (Single Battery)»(ref-184144-S12006988322005082200000) or «Battery Negative Cable Disconnect/Connect Procedure (Auxiliary Battery)»(ref-184144-S01033869922005082200000) in Engine Electrical.
2. Install the J 34730-1A . Refer to «Fuel Pressure Gage Installation and Removal»(ref-184137-S15792320592005082200000) .
3. Loosen the fuel fill cap in order to relieve fuel tank vapor pressure.
4. Open the valve on the J 34730-1A in order to bleed the system pressure. The fuel connections are now safe for servicing.
5. Drain any fuel remaining in the gage into an approved container.
6. Once the system pressure is completely relieved, remove the J 34730-1A . Refer to «Fuel Pressure Gage Installation and Removal»(ref-184137-S15792320592005082200000) .

Tools Required

J 34730-1A Fuel Pressure Gage

Quick Connect Fitting(s) Service (Metal Collar)

Tools Required

1. J 41769 Fuel Line Quick Disconnect Tool
2. J 43178 Fuel Line Disconnect Tool

Scheme 220

1. Relieve the fuel system pressure. Refer to «Fuel Pressure Relief Procedure»(ref-184137-S42170646662005082200000) .
2. Remove the retainer from the fuel feed line to engine quick-connect fitting.
3. If equipped with the 5.3L (L59) engine, remove the retainers from the fuel feed and return line to engine quick-connect fittings.
4. Using compressed air, blow any dirt or debris from around the fitting.
5. Using the correct tool from J 41769 , insert the tool into the female connector, then push inward in order to release the quick connect locking tabs.
6. If the vehicle is a cab/chassis, it may be necessary to use J 43178 in order to release the quick connect locking tabs.
7. Pull the fuel line connection apart.
8. Use a clean shop towel in order to wipe off the male connection end.
9. Inspect both ends of the fitting for dirt and burrs. Clean or replace the components as required.

J 45722 Fuel Sender Lock Ring Wrench

Scheme 221

1. Remove the fuel tank. Refer to «Fuel Tank Replacement (Pickup)»(ref-184137-S34389491612005082200000) or «Fuel Tank Replacement (Cab/Chassis - Front)»(ref-184137-S27423560502005082200000) or «Fuel Tank Replacement (Cab/Chassis - Rear)»(ref-184137-S31508324862005082200000) .
2. Disconnect the fuel line from the sending unit. Refer to «Quick Connect Fitting(s) Service (Plastic Collar)»(ref-184136-S07045263992005082200000) .
3. Disconnect the evaporative emission (EVAP) line from the sending unit. Refer to «Quick Connect Fitting(s) Service (Plastic Collar)»(ref-184136-S07045263992005082200000) .
4. Using J 45722 remove the sending unit lock ring. CAUTION: Drain the fuel from the fuel sender assembly into an approved container in order to reduce the risk of fire and personal injury. Never store the fuel in an open container.
5. Remove the sending unit and seal. Discard the seal.
6. Clean the sending unit sealing surfaces.

Fuel System Cleaning

1. Remove the sending unit. Refer to «Fuel Sender Assembly Replacement»(ref-184137-S14845045942005082200000) .
2. Inspect the fuel strainer. Replace a contaminated strainer and inspect the fuel pump.
3. Inspect the fuel pump inlet for dirt and debris. Replace the fuel pump if you find dirt or debris in the fuel pump inlet.
4. Flush the fuel tank with hot water.
5. Pour the water out of the sending unit opening. Rock the tank to be sure that removal of the water from the tank is complete.
6. Install the sending unit. Refer to «Fuel Sender Assembly Replacement»(ref-184137-S14845045942005082200000) .

Fuel Injector Cleaning Procedure

Tools Required

1. J 37287 Fuel Line Shut-Off Adapters
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.

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.

Scheme 222

1. Remove the engine sight shield. Refer to «Engine Sight Shield Replacement»(ref-184189-S12958489612005082200000) in Engine Mechanical - 8.1L.
2. Disconnect the evaporative emission (EVAP) canister purge valve electrical connector (1).
3. Disconnect the EVAP purge tube from the purge solenoid.
4. In order to disconnect the EVAP purge tube connector (1), slide the retaining tab (2) to the release position and separate the connection.
5. Remove the EVAP canister purge valve bolt.
6. Remove the EVAP canister purge valve.

Scheme 223

1. Install the EVAP canister purge valve. NOTE: Refer to Fastener Notice in Cautions and Notices.
2. Install the EVAP canister purge valve bolt. Tighten: Tighten the bolt to 10 N.m (89 lb in).
3. Connect the EVAP purge tube to the purge solenoid.
4. Connect the EVAP canister purge valve electrical connector (1).
5. Install the engine sight shield. Refer to «Engine Sight Shield Replacement»(ref-184189-S12958489612005082200000) in Engine Mechanical - 8.1L.

J 41413-200 EVAP Pressure/Purge Diagnostic Station

EVAP Cleaning Procedure

1. Remove the EVAP canister. Refer to «Evaporative Emission (EVAP) Canister Replacement (Pickup)»(ref-184137-S26464400382005082200000) or «Evaporative Emission (EVAP) Canister Replacement (Cab/Chassis)»(ref-184137-S10604109862005082200000) .
2. Turn OFF the main valve on the J 41413-200 .
3. Disconnect the hose from the diagnostic station pressure regulator.
4. Using a section of vacuum hose, connect one end to the diagnostic station pressure regulator.
5. Connect the other end of the vacuum hose to the canister side of the purge pipe.
6. Turn on the main nitrogen cylinder valve and continue to discharge nitrogen for 15 seconds.
7. If the nitrogen does not dislodge the carbon particles, replace the purge pipe.
8. Return the J 41413-200 to its original condition.
9. Install a new EVAP canister. Refer to «Evaporative Emission (EVAP) Canister Replacement (Pickup)»(ref-184137-S26464400382005082200000) or «Evaporative Emission (EVAP) Canister Replacement (Cab/Chassis)»(ref-184137-S10604109862005082200000) .
10. Install the EVAP canister purge valve. Refer to «Evaporative Emission (EVAP) Canister Purge Solenoid Valve Replacement»(ref-184137-S03573160122005082200000) .
11. Lower the vehicle.
12. Continue with the published service manual diagnostic DTC procedure.

Scheme 224

1. Disconnect the spark plug wire from the ignition coil. Twist the spark plug boot 1/2 turn. Pull only on the boot in order to remove the wire from the ignition coil.
2. Disconnect the ignition coil electrical connector.
3. Remove the ignition coil bolts.
4. Remove the ignition coil.

Powertrain

The powertrain has electronic controls to reduce exhaust emissions while maintaining excellent driveability and fuel economy. The powertrain control module (PCM) is the control center of this system. The PCM monitors numerous engine and vehicle functions. The PCM constantly looks at the information from various sensors and other inputs, and controls the systems that affect vehicle performance and emissions. The PCM also performs the diagnostic tests on various parts of the system. The PCM can recognize operational problems and alert the driver via the malfunction indicator lamp (MIL). When the PCM detects a malfunction, the PCM stores a diagnostic trouble code (DTC). The problem area is identified by the particular DTC that is set. The control module supplies a buffered voltage to various sensors and switches. Review the components and wiring diagrams in order to determine which systems are controlled by the PCM.

The following are some of the functions that the PCM controls

1. The engine fueling
2. The ignition control (IC)
3. The knock sensor (KS) system
4. The evaporative emissions (EVAP) system
5. The secondary air injection (AIR) system (if equipped)
6. The exhaust gas recirculation (EGR) system
7. The automatic transmission functions
8. The generator
9. The A/C clutch control
10. The cooling fan control

Powertrain Control Module Function

The powertrain control module (PCM) constantly looks at the information from various sensors and other inputs and controls systems that affect vehicle performance and emissions. The PCM also performs diagnostic tests on various parts of the system. The PCM can recognize operational problems and alert the driver via the malfunction indicator lamp (MIL). When the PCM detects a malfunction, the PCM stores a diagnostic trouble code (DTC). The problem area is identified by the particular DTC that is set. The control module supplies a buffered voltage to various sensors and switches. The input and output devices in the PCM include analog-to-digital converters, signal buffers, counters, and output drivers. The output drivers are electronic switches that complete a ground or voltage circuit when turned on. Most PCM controlled components are operated via output drivers. The PCM monitors these driver circuits for proper operation and, in most cases, can set a DTC corresponding to the controlled device if a problem is detected.

Trip

A trip is an interval of time during which the diagnostic test runs. A trip may consist of only a key cycle to power up the powertrain control module (PCM), allow the diagnostic to run, then cycle the key off to power down the PCM. A trip may also involve a PCM power up, meeting specific conditions to run the diagnostic test, then powering down the PCM. The definition of a trip depends upon the diagnostic. Some diagnostic tests run only once per trip (i.e., catalyst monitor) while other tests run continuously during each trip (i.e., misfire).

Warm-Up Cycle

The powertrain control module (PCM) uses warm-up cycles to run some diagnostics and to clear any diagnostic trouble codes (DTCs). A warm-up cycle occurs when the engine coolant temperature increases 22°C (40°F) from the start-up temperature. The engine coolant must also achieve a minimum temperature of 71°C (160°F). The PCM counts the number of warm-up cycles in order to clear the malfunction indicator lamp (MIL). The PCM will clear the DTCs when 40 consecutive warm-up cycles occur without a malfunction.

Fuel Tanks

The fuel tanks store the fuel supply. The primary fuel tank is located in the rear of the vehicle on the left side. On dual-tank applications, the secondary fuel tank is located in the rear of the vehicle above the spare tire. The fuel tanks are each held in place by 2 metal straps that attach to the frame. The fuel tanks are molded from high density polyethylene.

Fuel Filler Cap

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 fill pipe has a tethered fuel filler cap. A torque-limiting device prevents the cap from being over tightened. To install the cap, turn the cap clockwise until you hear audible clicks. This indicates that the cap is correctly torqued and fully seated. A built-in device indicates that the fuel filler cap is fully seated. A fuel filler cap that is not fully seated may cause a malfunction in the emission system.

Scheme 225

Scheme 226

Scheme 227

Scheme 228

The fuel sender assembly on single tank applications consists of the following major components

1. The fuel level sensor
2. The fuel tank pressure (FTP) sensor
3. The fuel tank fuel pump module
4. The fuel strainer
5. The fuel filter

The front fuel sender on dual tank applications consists of the following major components

1. The fuel level sensor
2. The fuel tank fuel pump module
3. The fuel strainer
4. The fuel filter

Scheme 229

The secondary fuel sender on dual tank applications consists of the following major components

1. The fuel level sensor (4)
2. The FTP sensor (1)
3. The rear fuel pump (2)

Scheme 230

The fuel level sensor consists of a float, a wire float arm, and a ceramic resistor cord. The position of the float arm indicates the fuel level. The fuel level sensor contains a variable resistor which changes resistance in correspondence with the amount of fuel in the fuel tank. The powertrain control module (PCM) sends the fuel level information via the class 2 circuit to the instrument panel cluster (IPC). This information is used for the instrument panel (I/P) fuel gage and the low fuel warning indicator, if applicable. The PCM also monitors the fuel level input for various diagnostics.

Fuel Pump

The fuel pump is mounted in the fuel sender assembly reservoir. The fuel pump is an electric high pressure pump. Fuel is pumped to the fuel rail at a specified flow and pressure. The fuel pump delivers a constant flow of fuel to the engine even during low fuel conditions and aggressive vehicle maneuvers. The powertrain control module (PCM) controls the electric fuel pump operation through a fuel pump relay. The fuel pump flex pipe acts to dampen the fuel pulses and noise generated by the fuel pump.

Fuel Strainer

The fuel strainer attaches to the lower end of the fuel sender. The fuel strainer is made of woven plastic. The functions of the fuel strainer are to filter contaminants and to wick fuel. The fuel strainer is self-cleaning and normally requires no maintenance. Fuel stoppage at this point indicates that the fuel tank contains an abnormal amount of sediment or water.

Nylon Fuel Pipes

Nylon pipes are constructed to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There are 2 sizes of nylon pipes used: 9.5 mm (3/8 in) ID for the fuel feed, and 12.7 mm (1/2 in) ID for the vent. Heat resistant rubber hose or corrugated plastic conduit protect the sections of the pipes that are exposed to chafing, high temperature, or 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 kink and restrict the fuel flow. Also, once exposed to fuel, nylon pipes may become stiffer and are more likely to kink if 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 inside the female connector hold the fittings together.

On-Board Refueling Vapor Recovery (ORVR) System

The On-Board Refueling Vapor Recovery (ORVR) System is an on-board vehicle system designed to recover fuel vapors during the vehicle refueling operation. The flow of liquid fuel down the fuel filler pipe provides a liquid seal which prevents 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.

Fuel Pipe O-Rings

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

Scheme 231

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
3. Integrates a fuel pulsation dampner (2) with the fuel metering system

Scheme 232

The Multec 2 fuel injector assembly is a solenoid operated device, controlled by the powertrain control module (PCM), that meters pressurized fuel to a single engine cylinder. The PCM energizes the high-impedance (12.2 ohms) injector solenoid (1) to open a normally closed ball valve (2). This allows fuel to flow into the top of the injector, past the ball valve, and through a director plate (3) at the injector outlet. The director plate has 2 machined holes that control the fuel flow, generating a spray of finely atomized fuel at the injector tip. Fuel from the injector tip is directed at the intake valve, causing it to become further atomized and vaporized before entering the combustion chamber. An injector stuck partly open can cause a loss of pressure after engine shutdown. Consequently, long cranking times would be noticed on some engines.

Fuel Pulsation Damper

The rapid opening and closing of the fuel injectors cause pressure fluctuation in the fuel rail. The result is that the amount of injected fuel will be more or less than the desired amount. Mounted on the fuel rail, the pulsation damper reduces these pressure fluctuations. When pressure suddenly begins top drop, the spring-loaded diaphragm extends slightly, decreasing fuel rail volume. This will momentarily prevent fuel pressure from becoming too low.

Starting Mode

With the ignition switch in the ON position, before engaging the starter, the powertrain control module (PCM) energizes the fuel pump relay for 2 seconds allowing the fuel pump to build up pressure. The PCM first tests speed density, then switches to the mass airflow (MAF) sensor. The PCM also uses the engine coolant temperature (ECT), the throttle position (TP), and the manifold absolute pressure (MAP) sensors to determine the proper air/fuel ratio for starting. The PCM 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 to the floor and then crank the engine. When the throttle position (TP) sensor is at wide open throttle (WOT), the powertrain control module (PCM) reduces the injector pulse width in order to increase the air to fuel ratio. The PCM holds this injector rate as long as the throttle stays wide open and the engine speed is below a predetermined RPM. If the throttle is not held wide open, the PCM returns to the starting mode.

Run Mode

The run mode has 2 conditions called Open Loop and Closed Loop. When the engine is first started and the engine speed is above a predetermined RPM, the system begins Open Loop operation. The powertrain control module (PCM) 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 upon the engine 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 PCM calculates the air/fuel ratio, injector on-time, based upon the signal from various sensors, but mainly from 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, airflow into the cylinders increases rapidly, while fuel flow tends to lag behind. To prevent possible hesitation, the powertrain control module (PCM) increases the pulse width to the injectors to provide extra fuel during acceleration. The PCM determines the amount of fuel required based upon the throttle position (TP), the coolant temperature, the manifold absolute pressure (MAP), the mass air flow (MAF), and the engine speed.

Deceleration Mode

When the driver releases the accelerator pedal, airflow into the engine is reduced. The powertrain control module (PCM) reads the corresponding changes in throttle position (TP), manifold absolute pressure (MAP), and mass air flow (MAF). The PCM 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 catalytic converters.

Battery Voltage Correction Mode

When the battery voltage is low, the powertrain control module (PCM) 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 the ignition dwell time

Fuel Cutoff Mode

The powertrain control module (PCM) 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 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 protect the catalytic converters

Short Term Fuel Trim

The Short Term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) signal voltages. These changes fine tune the engine fueling. The ideal fuel trim values are around 0 percent. A positive fuel trim value indicates that the powertrain control module (PCM) is adding fuel in order to compensate for a lean condition. A negative fuel trim value indicates that the PCM is reducing the amount of fuel in order to compensate for a rich condition.

When the PCM determines that the Short Term fuel trim is out of the operating range, the following DTCs will set

1. DTC P0171 Bank 1 Too Lean
2. DTC P0172 Bank 1 Too Rich
3. DTC P0174 Bank 2 Too Lean
4. DTC P0175 Bank 2 Too Rich

Long Term Fuel Trim

The Long Term fuel trim is a matrix of cells arranged by RPM and manifold absolute pressure (MAP). Each cell of the Long Term fuel trim is a register like the short term fuel trim. As the engine operating conditions change, the powertrain control module (PCM) will switch from cell to cell to determine what Long Term fuel trim factor to use in the base pulse width equation.

While in any given cell, the PCM also monitors the Short Term fuel trim. If the Short Term fuel trim is far enough from 0 percent, the PCM will change the Long Term fuel trim value. Once the Long Term fuel trim value is changed, the value change should force the Short Term fuel trim back toward 0 percent. If the mixture is still not correct, the short term fuel trim will continue to have a large deviation from the ideal 0 percent. In this case, the Long Term fuel trim value will continue to change until the Short Term fuel trim becomes balanced. Both the Short Term fuel trim and Long Term fuel trim have limits which vary by calibration. If the mixture is off enough so that Long Term fuel trim reaches the limit of Long Term fuel trim control and still cannot correct the condition, the Short Term fuel trim would also go to the Short Term fuel trim limit of control in the same direction. If the mixture is still not corrected by both short term fuel trim and Long Term fuel trim at their extreme values, a fuel trim diagnostic trouble code (DTC) will likely result. When the PCM determines that the Long Term fuel trim is out of the operating range, the following DTCs will set

1. DTC P0171 Bank 1 Too Lean
2. DTC P0172 Bank 1 Too Rich
3. DTC P0174 Bank 2 Too Lean
4. DTC P0175 Bank 2 Too Rich

Under the conditions of power enrichment (PE), the PCM sets the Short Term fuel trim to 0 percent and freezes it there until PE is no longer in effect. This is done so the Closed Loop factor and the long term fuel trim will not try to correct for the PE condition.

Check Gas Cap Message

The powertrain control module (PCM) sends a class 2 message to the driver information center (DIC) illuminating the Check Gas Cap message when any of the following occur

1. A malfunction in the evaporative emission (EVAP) system and a large leak test fails
2. A malfunction in the EVAP system and a small leak test fails

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 Valve

The EVAP purge solenoid valve controls the flow of vapors from the EVAP system to the intake manifold. The purge solenoid valve opens when commanded ON by the control module. This normally closed valve is pulse width modulated (PWM) by the control module to precisely control the flow of fuel vapor to the engine. The valve will also be opened during some portions of the EVAP testing, allowing engine vacuum to enter the EVAP system.

EVAP Vent Solenoid Valve

The EVAP vent solenoid valve controls fresh airflow into the EVAP canister. The valve is normally open. The control module commands the valve ON, closing the valve 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. A high FTP sensor voltage indicates a low fuel tank pressure or vacuum. A low FTP sensor voltage indicates a high fuel tank pressure.

EVAP Service Port

The EVAP service port is located in the EVAP purge pipe between the EVAP purge solenoid valve 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 PCM 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 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 PCM to quickly recognize which pair of cylinders are at top dead center (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 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 CMP sensor is also a magneto resistive sensor, with the same type of circuits as the 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 PCM 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 timing 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 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 feed and a ground. The PCM supplies a low reference and an ignition control (IC) circuit. Each ignition coil contains a solid state driver module. The PCM 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 PCM 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.

Powertrain Control Module (PCM)

The PCM controls all ignition system functions, and constantly corrects the basic spark timing. The PCM 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)

Purpose

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.