Chevrolet Equinox Service Manual: Fuel System Description Engine Control

Fuel System Overview

The fuel system is an electronic returnless on-demand design.A returnless fuel system reduces the internal temperature of thefuel tank by not returning hot fuel from the engine to the fueltank. Reducing the internal temperature of the fuel tank results inlower evaporative emissions.

An electric turbine style fuel pump attaches to the primaryfuel tank fuel pump module inside the fuel tank. The fuel pumpsupplies fuel through the fuel feed pipe to the high pressure fuelpump. The high pressure fuel pump supplies fuel to avariable-pressure fuel rail. Fuel enters the combustionchamber through precision multi-hole fuel injectors. Thehigh pressure fuel pump, fuel rail pressure, fuel injection timing,and injection duration are controlled by the engine control module(ECM).

The primary fuel tank fuel pump module also contains aprimary jet pump and a secondary jet pump. Fuel pump flow loss,caused by vapor expulsion in the pump inlet chamber, is diverted tothe primary jet pump and the secondary jet pump through arestrictive orifice located on the pump cover. The primary jet pumpfills the reservoir of the primary fuel tank fuel pump module . Thesecondary jet pump creates a venturi action which causes the fuelto be drawn from the secondary side of the fuel tank, through thefuel transfer pipe, to the primary side of the fuel tank.

Electronic Returnless Fuel System

The electronic returnless fuel system is a microprocessorcontrolled fuel delivery system which transports fuel from the tankto the fuel rail. It functions as an electronic replacement for atraditional, mechanical fuel pressure regulator. A pressure reliefregulator valve within the fuel tank provides an added measure ofover pressure protection. Desired fuel pressure is commanded by theengine control module (ECM), and transmitted to the fuel pump flowcontrol module via a GMLAN serial data message. A liquid fuelpressure sensor provides the feedback the fuel pump flow controlmodule requires for Closed Loop fuel pressure control.

Fuel Pump Flow Control Module

The fuel pump flow control module is a serviceable GMLANmodule. The fuel pump flow control module receives the desired fuelpressure message from the engine control module (ECM) and controlsthe fuel pump located within the fuel tank to achieve the desiredfuel pressure. The fuel pump flow control module sends a25-kHz-PWM signal to the fuel pump, and pumpspeed is changed by varying the duty cycle of this signal. Maximumcurrent supplied to the fuel pump is 15-amps. A liquidfuel pressure sensor provides fuel pressure feedback to the fuelpump flow control module.

Fuel Pressure Sensor

The fuel pressure sensor is a serviceable 5-V,3-pin device. It is located on the fuel feed lineforward of the fuel tank, and receives power and ground from thefuel pump flow control module through a vehicle wiring harness. Thesensor provides a fuel pressure signal to the fuel pump flowcontrol module, which is used to provide Closed Loop fuel pressurecontrol.

Flex Fuel Sensor

The flex fuel sensor measures the ethanol-gasolineratio of the fuel being used in a flexible fuel vehicle. Flexiblefuel vehicles can be operated with a blend of ethanol and gasoline,up to 85-percent ethanol. In order to adjust theignition timing and the fuel quantity to be injected, the enginemanagement system requires information about the percentage ofethanol in the fuel.

The flex fuel sensor uses quick-connect style fuelconnections, an incoming fuel connection, and an outgoing fuelconnection. All fuel passes through the flex fuel sensor beforecontinuing on to the fuel rail. The flex fuel sensor measures twodifferent fuel related parameters, and sends an electrical signalto the engine control module (ECM) to indicate ethanol percentage,and fuel temperature.

The flex fuel sensor has a three-wire electricalharness connector. The three wires provide a ground circuit, apower source, and a signal output to the ECM. The power source isbattery positive voltage and the ground circuit connects to anengine ground. The signal circuit carries both the ethanolpercentage and fuel temperature within the same signal, on the samewire.

The flex fuel sensor uses a microprocessor inside the sensorto measure the ethanol percentage and fuel temperature, and changesthe output signal accordingly. The electrical characteristic of theflex fuel sensor signal is a square-wave digital signal. The signalis both variable frequency and variable pulse width. The frequencyof the signal indicates the ethanol percentage, and the pulse widthindicates the fuel temperature. The ECM provides an internalpull-up to 5-V on the signal circuit, and theflex fuel sensor pulls the 5-V to ground in pulses. Theoutput frequency is linear to the percentage of ethanol content inthe fuel. The normal range of operating frequency is between 50 and150-Hz, with 50-Hz representing0-percent ethanol, and 150-Hz representing100-percent ethanol. The normal pulse width range of thedigital pulses is between 1 and 5-ms, with1-ms representing −40°C(−40°F), and 5-ms representing151.25°C (304.25°F).

The microprocessor inside the sensor is capable of a certainamount of self-diagnosis. An output frequency of 180-Hzindicates either that the fuel is contaminated, or that an internalsensor electrical fault has been detected. Certain substancesdissolved in the fuel can cause the fuel to be contaminated,raising the output frequency higher than the actual ethanolpercentage should indicate. Examples of these substances includewater, sodium chloride (salt), and methanol.

It should be noted that it is likely that the flex fuelsensor will indicate a slightly lower ethanol percentage than whatis advertised at the fueling station. This is not a fault of thesensor. The reason has to do with government requirements foralcohol-based motor fuels. Government regulations require thatalcohol intended for use as motor fuel be denatured. This meansthat 100-percent pure ethanol is first denatured withapproximately 4½-percent gasoline, beforebeing mixed with anything else. When an ethanol gasoline mixture isadvertised as E85, the 85-percent ethanol was denaturedbefore being blended with gasoline, meaning an advertised E85 fuelcontains only about 81-percent ethanol. The flex fuelsensor measures the actual percentage of ethanol in thefuel.

Fuel Tank

The fuel tank stores the fuel supply. The fuel tank islocated in the rear of the vehicle. The fuel tank is held in placeby 2-metal straps that attach to the underbody of thevehicle. The fuel tank is molded from high-densitypolyethylene.

The fuel tank is a saddle configuration. Because of thesaddle shape of the tank, two fuel pump modules arerequired.

Fuel Fill Pipe

The fuel fill pipe has a built-in restrictor in order toprevent refueling with leaded fuel.

Fuel Filler Cap

The fuel fill pipe has a tethered fuel filler cap. Atorque-limiting device prevents the cap from being over-tightened.To install the cap, turn the cap clockwise until you hear audibleclicks. This indicates that the cap is correctly torqued and fullyseated.

Fuel Tank Fuel Pump Module

An electric turbine style fuel pump attaches to the primaryfuel tank fuel pump module inside the fuel tank. The fuel pumpsupplies fuel through the fuel feed pipe to the high pressure fuelpump. The fuel tank fuel pump module contains a reverse flow checkvalve. The check valve maintains fuel pressure in the fuel feedpipe in order to prevent long cranking times.

Primary Fuel Tank Fuel Pump Module

The primary fuel tank fuel pump module is located inside ofthe right side of the fuel tank. The primary fuel tank fuel pumpmodule consists of the following major components:

The fuel level sensorThe fuel pump and reservoir assemblyThe fuel filterThe pressure relief regulator valveThe fuel strainerThe primary jet pumpThe secondary jet pumpSecondary Fuel Tank Fuel Pump Module

The secondary fuel tank fuel pump module is located inside ofthe left side of the fuel tank. The secondary fuel tank fuel pumpmodule consists of the following major components:

The fuel level sensorThe fuel pick-upFuel Level Sensor

The primary fuel level sensor and the secondary fuel levelsensor change resistance based on fuel level. The engine controlmodule (ECM) monitors the signal circuits of the primary fuel levelsensor and the secondary fuel level sensor in order to determinethe fuel level. When the fuel tank is full, the resistances of bothfuel level sensors are low and the ECM senses a low signal voltageon both the signal circuits of the primary fuel level sensor andthe secondary fuel level sensor. When the fuel tank is empty, theresistances of the fuel level sensors are high and the ECM senses ahigh signal voltage. The ECM uses the signal circuits of theprimary fuel level sensor and the secondary fuel level sensor inorder to calculate the percentage of remaining fuel in the tank.The ECM sends the fuel level percentage via High Speed CAN-Bus tothe body control module (BCM). The BCM then sends the fuel levelpercentage via Low Speed CAN-Bus to the instrument cluster in orderto control the fuel gauge.

Fuel Pump

The fuel pump is mounted in the primary fuel tank fuel pumpmodule reservoir. The fuel pump is an electric pump. Fuel is pumpedto the high pressure fuel pump at a pressure that is based onfeedback from the fuel pressure sensor. The fuel pump delivers aconstant flow of fuel even during low fuel conditions andaggressive vehicle maneuvers. The fuel pump flex pipe acts todampen the fuel pulses and noise generated by the fuel pump.

Pressure Relief Regulator Valve

The pressure relief regulator valve replaces the typical fuelpressure regulator used on a mechanical returnless fuel system. Thepressure relief regulator valve is closed during normal vehicleoperation. The pressure relief regulator valve is used to ventpressure during hot soaks and also functions as a fuel pressureregulator in the event of the fuel pump flow control moduledefaulting to 100-percent pulse width modulation (PWM)of the fuel pump. Due to variation in the fuel system pressures,the opening pressure for the pressure relief regulator valve is sethigher than the pressure that is used on a mechanical returnlessfuel system pressure regulator.

Primary and Secondary Jet Pumps

The primary jet pump is located in the primary fuel tank fuelpump module. Fuel pump flow loss, caused by vapor expulsion in thepump inlet chamber, is diverted to the primary jet pump and thesecondary jet pump through a restrictive orifice located on thepump cover. The primary jet pump fills the reservoir of the primaryfuel tank fuel pump module.

The secondary jet pump creates a venturi action which causesthe fuel to be drawn from the secondary side of the fuel tank,through the transfer pipe, to the primary side of the fueltank.

Nylon Fuel Pipes

Warning:In order to reduce the risk of fire and personal injuryobserve the following items:

Replace all nylon fuel pipes that are nicked, scratched ordamaged during installation, do not attempt to repair the sectionsof the nylon fuel pipesDo not hammer directly on the fuel harness body clips wheninstalling new fuel pipes. Damage to the nylon pipes may result ina fuel leak.Always cover nylon vapor pipes with a wet towel before usinga torch near them. Also, never expose the vehicle to temperatureshigher than 115°C (239°F) for more than one hour,or more than 90°C (194°F) for any extendedperiod.Apply a few drops of clean engine oil to the male pipe endsbefore connecting fuel pipe fittings. This will ensure properreconnection and prevent a possible fuel leak. (During normaloperation, the O-rings located in the female connector will swelland may prevent proper reconnection if not lubricated.)

Nylon pipes are constructed to withstand maximum fuel systempressure, exposure to fuel additives, and changes intemperature.

Heat resistant rubber hose or corrugated plastic conduitprotect the sections of the pipes that are exposed to chafing, hightemperature, or vibration.

Nylon fuel pipes are somewhat flexible and can be formedaround gradual turns under the vehicle. However, if nylon fuelpipes are forced into sharp bends, the pipes kink and restrict thefuel flow. Also, once exposed to fuel, nylon pipes may becomestiffer and are more likely to kink if bent too far. Take specialcare when working on a vehicle with nylon fuel pipes.

Quick-Connect Fittings

Quick-connect fittings provide a simplified means ofinstalling and connecting fuel system components. The fittingsconsist of a unique female connector and a compatible male pipeend. O-rings, located inside the female connector, provide the fuelseal. Integral locking tabs inside the female connector hold thefittings together.

High Pressure Fuel Pump

The high fuel pressure necessary for direct injection issupplied by the high pressure fuel pump. The pump is mounted on therear of the engine and is driven by a three-lobe cam on the Bank 2exhaust camshaft. This pump also regulates the fuel pressure usingan actuator in the form of an internal solenoid-controlled valve.In order to keep the engine running efficiently under all operatingconditions, the engine control module (ECM) requests pressureranging from 2 to 15-MPa (290 to 2176-psi),depending on engine speed and load. Output drivers in the ECMprovide the pump control circuit with a 12-V pulse-widthmodulated (PWM) signal, which regulates fuel pressure by closingand opening the control valve at specific times during pumpstrokes. This effectively regulates the portion of each pump strokethat is delivered to the fuel rail. When the control solenoid isNOT powered, the pump operates at maximum flow rate. In the eventof pump control failure, the high pressure system is protected by arelief valve in the pump that prevents the pressure from exceeding17.5-MPa (2538-psi).

Fuel Rail Assembly

The fuel rail assembly attaches to the cylinder head. Thefuel rail distributes high pressure fuel to the fuel injectors. Thefuel rail assembly consists of the following components:

The direct fuel injectorsThe fuel rail pressure sensorFuel Injectors

The fuel injection system is a high pressure, directinjection, returnless on-demand design. The fuelinjectors are mounted in the cylinder head beneath the intake portsand spray fuel directly into the combustion chamber. Directinjection requires high fuel pressure due to the fuel injector'slocation in the combustion chamber. Fuel pressure must be higherthan compression pressure requiring a high pressure fuel pump. Thefuel injectors also require more electrical power due to the highfuel pressure. The ECM supplies a separate high voltage supplycircuit and a high voltage control circuit for each fuel injector.The injector high voltage supply circuit and the high voltagecontrol circuit are both controlled by the ECM. The ECM energizeseach fuel injector by grounding the control circuit. The ECMcontrols each fuel injector with 65-V. This iscontrolled by a boost capacitor in the ECM. During the65-V boost phase, the capacitor is discharged through aninjector, allowing for initial injector opening. The injector isthen held open with 12-V.

The fuel injector assembly is an inside opening electricalmagnetic injector. The injector has six precision machined holesthat generate a cone shaped oval spray pattern. The fuel injectorhas a slim extended tip in order to allow a sufficient coolingjacket in the cylinder head.

Fuel Injection Fuel Rail Fuel Pressure Sensor

The fuel rail pressure sensor detects fuel pressure withinthe fuel rail. The engine control module (ECM) provides a5-V reference voltage on the 5-V referencecircuit and ground on the reference ground circuit. The ECMreceives a varying signal voltage on the signal circuit. The ECMmonitors the voltage on the fuel rail pressure sensor circuits.When the fuel pressure is high, the signal voltage is high. Whenthe fuel pressure is low, the signal voltage is low.

Fuel Metering Modes of Operation

The ECM monitors voltages from several sensors in order todetermine how much fuel to give the engine. The ECM controls theamount of fuel delivered to the engine by changing the fuelinjector pulse width. The fuel is delivered under one of severalmodes.

Starting Mode

The ECM supplies voltage to the fuel pump control module whenthe ECM detects that the ignition is ON. The voltage from the ECMto the fuel pump control module remains active for 2-s,unless the engine is in Crank or Run. While this voltage is beingreceived, the fuel pump control module closes the ground switch ofthe fuel tank fuel pump module and also supplies a varying voltageto the fuel tank fuel pump module in order to maintain the desiredfuel line pressure. The ECM calculates the air/fuel ratio based oninputs from the engine coolant temperature (ECT), manifold absolutepressure (MAP), mass air flow (MAF), and throttle position sensors.The system stays in starting mode until the engine speed reaches apredetermined RPM.

During a cold start, the engine control module (ECM) commandsdual-pulse mode during Open Loop operation to improvecold start emissions. In dual-pulse mode, the injectorsare energized twice during each injection event.

Clear Flood Mode

If the engine floods, the engine can be cleared by pressingthe accelerator pedal down to the floor and then cranking theengine. When the throttle position sensor is at wide open throttle(WOT), the ECM reduces the fuel injector pulse width in order toincrease the air to fuel ratio. The ECM holds this injector rate aslong as the throttle stays wide open and the engine speed is belowa predetermined RPM. If the throttle is not held wide open, the ECMreturns to the starting mode.

Run Mode

The run mode has 2 conditions called Open Loop and ClosedLoop. When the engine is first started and the engine speed isabove a predetermined RPM, the system begins Open Loop operation.The ECM ignores the signal from the heated oxygen sensor (HO2S).The ECM calculates the air/fuel ratio based on inputs from theengine coolant temperature (ECT), manifold absolute pressure (MAP),mass air flow (MAF), and throttle position sensors. The systemstays in Open Loop until meeting the following conditions:

The HO2S has varying voltage output, showing that the HO2S ishot enough to operate properly.The ECT sensor is above a specified temperature.A specific amount of time has elapsed after starting theengine.

Specific values for the above conditions exist for eachdifferent engine, and are stored in the electrically erasableprogrammable read-only memory (EEPROM). The system begins ClosedLoop operation after reaching these values. In Closed Loop, the ECMcalculates the air/fuel ratio, injector ON time, based upon thesignal from various sensors, but mainly from the HO2S. This allowsthe air/fuel ratio to stay very close to 14.7:1.

Acceleration Mode

When the driver pushes on the accelerator pedal, air flowinto the cylinders increases rapidly. To prevent possiblehesitation, the ECM increases the pulse width to the injectors toprovide extra fuel during acceleration. This is also known as powerenrichment. The ECM determines the amount of fuel required basedupon throttle position, engine coolant temperature (ECT), manifoldabsolute pressure (MAP), mass air flow (MAF), and enginespeed.

Deceleration Mode

When the driver releases the accelerator pedal, air flow intothe engine is reduced. The ECM monitors the corresponding changesin throttle position, mass air flow (MAF), and manifold absolutepressure (MAP). The ECM shuts OFF fuel completely if thedeceleration is very rapid, or for long periods, such as long,closed-throttle coast-down. The fuel shuts OFF in order to preventdamage to the catalytic converters.

Battery Voltage Correction Mode

When the battery voltage is low, the ECM compensates for theweak spark delivered by the ignition system in the followingways:

Increasing the amount of fuel deliveredIncreasing the idle RPMIncreasing the ignition dwell timeFuel Cutoff Mode

The ECM cuts OFF fuel from the fuel injectors when thefollowing conditions are met in order to protect the powertrainfrom damage and improve driveability:

The ignition is OFF. This prevents engine run-on.The ignition is ON but there is no ignition reference signal.This prevents flooding or backfiring.The engine speed is too high, above red line.The vehicle speed is too high, above rated tire speed.During an extended, high speed, closed throttle coastdown—This reduces emissions and increases enginebraking.During extended deceleration, in order to prevent damage tothe catalytic convertersFuel Trim

The ECM controls the air/fuel metering system in order toprovide the best possible combination of driveability, fueleconomy, and emission control. The ECM monitors the heated oxygensensor (HO2S) signal voltage while in Closed Loop and regulates thefuel delivery by adjusting the pulse width of the injectors basedon this signal. The ideal fuel trim values are around0-percent for both short and long term fuel trim. Apositive fuel trim value indicates the ECM is adding fuel in orderto compensate for a lean condition by increasing the pulse width. Anegative fuel trim value indicates that the ECM is reducing theamount of fuel in order to compensate for a rich condition bydecreasing the pulse width. A change made to the fuel deliverychanges the long and short term fuel trim values. The short termfuel trim values change rapidly in response to the HO2S signalvoltage. These changes fine tune the engine fueling. The long termfuel trim makes coarse adjustments to fueling in order to re-centerand restore control to short term fuel trim. A scan tool can beused to monitor the short and long term fuel trim values. The longterm fuel trim diagnostic is based on an average of several of thelong term speed load learn cells. The ECM selects the cells basedon the engine speed and engine load. If the ECM detects anexcessively lean or rich condition, the ECM will set a fuel trimdiagnostic trouble code (DTC).