Electronic Control System Gas Plus Engines – 101-007   Electronic Controlled Fuel System

This section provides an overview of how fuel and air flow through the engine.

For a detailed description of the individual components, refer to the ECM Inputs and ECM Outputs sections under Electronic Engine Controls.

The engine receives gaseous fuel that is regulated to a certain pressure by the primary regulator. The primary regulator is an OEM-installed component.

The fuel passes through the primary fuel filter before entering the engine. This filter is to remove any oil that is suspended in the fuel. Oil can cause performance problems if it accumulates in the fuel system.

The primary fuel pressure sensor allows the ECM to monitor the inlet fuel pressure.

When the filtered fuel enters the engine, the secondary pressure regulator lowers the fuel pressure to a lower value specific for each model.

The fuel then passes through the fuel shutoff valve. The fuel shutoff valve is a solenoid that is either open or closed.

It then passes a fuel detection point, the secondary fuel pressure sensor, located before the fuel control valve, the secondary fuel pressure sensor. The fuel control valve is also located in the mixer housing.

Then the fuel proceeds through the gas mass flow sensor. The gas mass flow sensor measures the gas flow through the fuel system.

The fuel is then mixed with the combustion air in the mixer. The combustion air will have been compressed in the turbocharger compressor and then cooled in the charge air cooler.

After the fuel and air are combined, the mixture passes through the throttle actuator.

After passing through the throttle actuator, the fuel/air mixture enters the intake manifold and then into the cylinders for combustion. The intake manifold air pressure/temperature sensor is located in the intake manifold.

This pressure and temperature information is used to adjust the air to fuel ratio to meet the desired engine performance.

As the exhaust exits the turbocharger turbine, the heated oxygen sensor measures the amount of oxygen in the exhaust. The ECM can calculate the engine’s actual air/fuel ratio given the amount of oxygen in the exhaust.

The ignition process begins with the electronic control module (ECM) sending ignition information to the ignition control module (ICM).

Based on the commands from the ECM, the ICM sends firing signals to the individual coils. Each cylinder has its own coil. These firing signals are approximately 300 VDC.

The coils amplify the ICM signals and fire the spark plugs. The signals sent from the coils are approximately 10,000 to 25,000 VDC.

C Gas Plus and L Gas Plus engines use a coil-on-plug arrangement. Each coil is located directly above the spark plug.

B Gas Plus, B LPG Plus and B Gas International (B Gas International) —engines use ignition coil packs which are located on the intake manifold. A high voltage wire is used to complete the connection to the spark plug.

The ECM receives signals from the following sources (not all engines are equipped with all sensors listed):

• Engine position sensor
• Throttle position sensor (internal to throttle actuator)
• Engine coolant temperature sensor
• Intake manifold air pressure/temperature sensor
• Mixer inlet pressure sensor
• Gas mass flow sensor
• Heated oxygen sensor
• Diagnostic switch
• Fuel pressure sensor, primary
• Fuel pressure sensor, secondary
• Engine oil pressure/temperature sensor
• Knock sensors (two)
• Exhaust back pressure sensor
• Vehicle speed sensor (VSS)
• Switched inputs
• Accelerator pedal
• Humidity sensor
• Compressor inlet temperature (L Gas Plus)
• Air inlet restriction sensor (L Gas Plus).

The B Gas Plus, B LPG Plus, B Gas International and C Gas Plus engines use an engine position sensor that measures engine speed by counting notches in the cam gear as the gear rotates. The sensor uses a 6 + 1 system where there are 6 evenly spaced notches in the cam gear with an extra notch between two of the evenly spaced notches. This allows the ECM to accurately measure engine speed, while the one extra notch tells the ECM the exact position of the camshaft. This information allows the ECM to control the spark timing.

The L Gas Plus engine uses an engine speed/position sensor that measures engine speed by counting notches in the camshaft tone wheel as the wheel rotates. The tone wheel has one location with a double wide space that identifies Top Dead Center of the number one cylinder. This allows the ECM to accurately measure engine speed, while the one extra notch tells the ECM the exact position of the camshaft. This information allows the ECM to control the spark timing.

The L Gas Plus engine uses a secondary engine speed/position sensor that measures engine speed by counting notches in the crankshaft tone wheel as the wheel rotates. This allows the ECM to accurately measure engine speed. This information allows the ECM to control the spark timing and overspeed protection.

The throttle position sensor is internal to the throttle actuator and measures the position of the throttle plate. The ECM controls the throttle position to regulate speed against fueling.

The intake manifold air pressure/temperature sensor is a combination sensor. The absolute air pressure side determines the pressure of the air/fuel mixture in the intake manifold by measuring the capacitance of two circular plates in the sensor. As the manifold pressure changes, the distance between the plates changes, causing a change in the capacitance of the plates. The sensor has a built-in printed circuit board that converts the capacitance measurement to a signal the ECM can use. The temperature side determines the temperature of the air/fuel mixture in the manifold. This is done by measuring the resistance of the sensor. The ECM receives this signal and measures the voltage drop across a known resistance in the ECM that is in series with the sensor.

NOTE: This is an absolute pressure sensor.

The engine coolant temperature sensor determines the coolant temperature in the cylinder head. This is done by measuring the resistance of the sensor. The ECM receives this signal and measures the voltage drop across a known resistance in the ECM that is in series with the sensor.

The L Gas Plus engine also uses this sensor to measure coolant pressure and functions as the other combination pressure/temperature sensors on the engine.

The mixer inlet pressure sensor determines the pressure of the air (boost pressure), before it’s combined with fuel in the mixer. This is accomplished by measuring capacitance of two circular plates in the sensor. As the mixer inlet pressure changes, the distance between the plates changes, causing a change in the capacitance of the plates. The sensor has a built-in printed circuit board that converts the capacitance measurement to a signal the ECM can use.

NOTE: This is an absolute pressure sensor.

The gas mass flow sensor (GMFS) determines the amount of fuel being mixed with intake air. The sensor is a hot wire anemometer that measures the amount of power required to keep an electrically heated wire at a constant temperature. The wire requires more power to maintain a constant temperature as more fuel flows by the wire. The sensor has a built in printed circuit board that controls the sensor. In order for the gas mass flow sensor to function properly, the fuel must be free of turbulence and have no oil contamination. A screen pack is installed after the fuel shutoff valve to minimize fuel turbulence.

The heated oxygen sensor (HOS) determines the amount of oxygen in the exhaust stream. The amount of oxygen in the exhaust shows in Lambda as the engine operates. The sensor contains a ceramic element that allows oxygen ions to migrate through it. The difference in oxygen concentration on either side of the element determines the rate that ions pass through it. In turn, this creates an electrical signal that the ECM measures.

NOTE: Do not apply lubricant to the heated oxygen sensor connector.

The diagnostic switch is a momentary switch that tells the ECM to begin flashing out fault codes on the diagnostic lamp. The diagnostic switch is an OEM installed component that is generally located in the vehicle cab.

The primary fuel pressure sensor is located in the low pressure housing and measures fuel pressure supplied to the low pressure regulator.

The secondary fuel pressure/temperature sensor is located in the mixer housing and measures secondary fuel pressure and temperature. The ECM uses this pressure to calculate fuel flow.

The B Gas Plus, B LPG. Plus and C Gas Plus engines use an engine oil pressure/temperature sensor located in the oil rifle. It measures the pressure and temperature of the engine oil. The temperature side determines the temperature of the oil. This is done by measuring the resistance of the sensor. The ECM receives this signal and measures the voltage drop across a known resistance in the ECM that is in series with the sensor.

The L Gas Plus engine only uses an oil pressure sensor.

The B Gas International engine does not use an oil pressure sensor.

The knock sensors are two sensors on the engine to determine knock. These are located on the block and cylinder head. These sensors measure frequency to determine pre-spark ignition. The two sensors will provide readings for all six cylinders.

The exhaust back pressure sensor measures the exhaust back pressure and takes its reading next to the heated oxygen sensor location. This provides an input into the fuel system.

The vehicle speed (VSS) sensor measures the rotation of the transmission tailshaft gear teeth as it passes in front of the sensor. The ECM must be programmed with appropriate values and a number of vehicle parameters for it to calculate vehicle speed. The INSITE™ electronic service tool is used to set vehicle specific parameters.

The ECM has a number of features controlled by switched inputs. Cruise control, PTO, remote power take off, door interlock, and failure overrides features are all controlled by switched inputs.

The B Gas Plus, B LPG. Plus and C Gas Plus engines uses a standard electronic pedal containing a pedal position sensor and an idle validation switch, the ECM uses the input from these in the engine governing system.

The B Gas International engine has a mechanical throttle cable that connects the accelerator pedal to the mechanical throttle plate.

The humidity sensor measures relative humidity of the intake air. The sensor is located in the intake elbow before the air/fuel mixture occurs. The ECM uses the pressure, temperature, and relative humidity of the intake air stream and calculates specific humidity.

The ECM controls the following outputs:

• Fuel shutoff valve
• Turbocharger control valve
• Fuel control valve
• Spark reference signal
• Spark timing signal
• Datalink
• Throttle actuator.

The fuel shutoff valve actuator is an on/off solenoid valve used to cut off the fuel to the engine. The valve allows fuel to flow when power is applied and shuts automatically when power is removed. Power is only supplied when engine rpm is above zero. Under certain fault conditions the ECM will close the valve. The fuel shutoff valve requires a minimum of 9.5 VDC to open.

NOTE: The fuel shut off valve opens for two seconds when the ignition keyswitch is turned on.

The wastegate control valve is directed by the ECM to control the pressure to the wastegate actuator. It allows the wastegate actuator to open or close depending on the difference between the atmospheric pressure and boost pressure needed by the engine. The mixer inlet pressure sensor is used by the ECM to determine the current boost levels.

The fuel control valve is used to control the amount of fuel mixed with the intake air. The ECM precisely determines the amount the valve should be open under operating conditions from inputs from the heated oxygen sensor and the gas mass flow sensor.

The spark reference signal from the ECM to the ignition control module sends the next spark timing signal to the correct cylinder. Input from the engine position sensor allows the ECM to determine the correct location in the firing order.

The spark timing signal from the ECM tells the ICM which spark plug to fire next in the firing order. The ECM calculates the spark timing depending on engine operating conditions.

NOTE: Spark timing is not adjustable.

The L Gas Plus engine uses a two connector style ICM that has the ability to monitor and report to the ECM cylinder misfires. Presently this ICM design is only used on the L Gas Plus and is not interchangeable with the B or C Gas Plus engines.

The datalink ECM broadcasts information over the datalink which can be used by both the INSITE™ electronic service tool and industry standard diagnostic tools. Two protocols can be used: SAE J1708 and J1939.

The B Gas Plus and C Gas Plus engines use a electronic throttle actuator.

The throttle actuator controls the position of the throttle plate. The ECM sends a signal to the actuator which in turn opens or closes the throttle plate. The ECM uses the measured position to control fueling.

The B Gas International engine uses a mechanical throttle plate controlled with a linkage to the accelerator pedal. The ECM uses a position sensor mounted on the throttle body to determine the throttle plate position.

The ECM is responsible for the following functions:

• Air/fuel ratio control
• Ignition timing control
• Turbocharger control
• Starting sequence
• Overspeed control
• Engine speed governing
• Diagnostics.

The air/fuel ratio control is determined by the ECM through engine sensor input. The ECM’s fueling estimate is composed of two parts. The open and closed loop fueling estimate.

The open loop fueling estimate is determined by dividing the air flow by the desired air/fuel ratio. The estimated air flow depends on input from various sensors and is determined from a table in the ECM. This open loop fueling estimate is only used during startup and under certain fault conditions.

The closed loop fueling estimate adjusts the open loop fueling estimate after the heated oxygen sensor has warmed up. The heated oxygen sensor will inform the ECM if the engine is running lean or rich, and will adjust the fueling accordingly. If the closed loop estimate is equal to 0, then no adjustment needs to be made.

Heated oxygen sensor compensation is a monitor parameter in INSITE™ electronic service tool which shows the closed loop estimate as a percentage of the maximum allowable closed loop adjustment. A positive or negative value indicates the heated oxygen sensor is causing the ECM to add or take away fuel.

Whether in the open or closed loop mode, the ECM uses the input from the gas mass flow sensor to direct the fuel control valve to allow more or less fuel flow.

Monitor mode parameter in INSITE™ electronic service tool that shows the measured gas flow minus the command gas flow. A positive value indicates more gas flow is indicated than commanded. A negative value indicates less gas flow is indicated than commanded. The value should stay close to 0 if the engine is working correctly.

The Ignition Timing Control is controlled by the ECM using engine speed and intake manifold pressure to calculate ignition timing. The engine position sensor informs the ECM when to fire the spark plugs.

NOTE: The ignition timing is not adjustable.

The B Gas Plus, B LPG. Plus, B Gas International and C Gas Plus engines uses a wastegate control valve and is controlled by the ECM to control the pressure to the wastegate actuator between atmospheric and boost pressures. The wastegate control valve will open or close to allow the boost pressure to increase or decrease. The mixer inlet absolute pressure sensor is used by the ECM to determine the current boost levels.

The L Gas Plus engines uses a turbocharger control valve to control the amount of movement of the variable geometry turbocharger (VGT). The control valve has a 12 VDC power supply as well as a 5 VDC pulse width modulating control signal. The valve controls the amount of vehicle air pressure supplied to the variable geometry turbocharger.

The Starting Sequence is initiated by turning the key to the ON position and supplies power to the ECM. In the START position the starter motor is energized.

The Overspeed Control is controlled by the ECM to shut off the fuel if the engine rpm gets too high. This does not hurt the engine. However, another limit at a higher rpm will set the overspeed fault. The overspeed fault code indicates a malfunction or improper operation.

The Engine Speed Governing controls the position of the throttle plate. The ECM sends a signal to the actuator which in turn opens or closes the throttle plate. The ECM uses the measured position to control fueling. Governing can be engine or vehicle speed based.

The Gas Plus engines are equipped with an engine protection system. The system monitors critical engine temperatures and pressures and will log diagnostic faults when an over- or under normal operating condition occurs. If an out of range condition exists, and engine derate action is to be initiated, the operator will be alerted by an in-cab WARNING lamp. When the red STOP lamp is illuminated, the driver must pull to the side of the road, when it is safe to do so, to reduce the possibility of engine damage.

The engine protection system monitors the following inputs:

• Coolant temperature
• Coolant level
• Engine oil pressure
• Engine oil temperature (B, B LPG. and C Gas Plus)
• Exhaust back pressure
• Intake manifold temperature
• Engine overspeed
• Fuel pressure
• Mixer inlet (boost) pressure
• Engine knock (detonation)
• Throttle control
• Coolant pressure (L Gas Plus).

NOTE: Engine power and speed will be gradually reduced depending on the level of severity of the observed condition. The engine protection system will not shut down the engine unless the engine protection shutdown feature has been enabled. Except if a loss of throttle control fault code occurs, the engine will shut down immediately.

Engine Protection Shutdown feature automatically shuts off the engine when the temperature, pressure, or coolant level sensors indicate the engine is operating over or under normal operating conditions.

Except for throttle control, the red STOP lamp in the cab will flash for 30 seconds prior to shutdown to alert the driver.

If a loss of throttle control fault code occurs, the engine will shut down immediately.

The Gas Plus engine control system can show and record operation anomalies that present themselves as fault codes. These codes will make troubleshooting easier. The fault codes are recorded in the electronic control module (ECM). They can be read using the fault lamps in the dash or with the INSITE™ electronic service tool.

NOTE: Not all engine control system anomalies are shown as fault codes.

There are three types of system codes:

• Engine electronic control system fault codes
• Engine protection system fault codes
• Engine maintenance indicator codes.

All fault codes recorded will be either active (fault code is currently active on the engine) or inactive (fault code was active at some time, but at the moment, is not active).

Most, but not all, of the electronic fault codes will light a lamp when they are active. There are two possible lamps that can be illuminated when a fault code is active:

• The WARNING or CHECK ENGINE lamp is amber and indicates the need to repair the fault at the first available opportunity. This lamp will also illuminate when an engine maintenance function needs to be performed.
• The STOP or STOP ENGINE lamp is red and indicates the need to stop the engine as soon as it can be safely done. The engine should remain shut down until the fault can be repaired.

Some vehicles have a low fuel pressure lamp. The low fuel pressure lamp will illuminate if the primary fuel pressure sensor detects that the supply pressure to the engine is below specifications.

To check for active engine electronic system fault codes and maintenance indicator codes, turn the ignition switch to the OFF position, and move the diagnostic switch to the ON position, or connect the shorting plug into the diagnostic connector.

Turn the vehicle ignition switch to the ON position.

If no active fault codes are recorded, both WARNING and STOP lamps will illuminate and stay on.

If active fault codes are recorded, both WARNING and STOP lamps will illuminate momentarily, then begin to flash the codes of the recorded faults.

The fault code will flash in the following sequence:

• A amber WARNING lamp will flash.
• There is a short one or two second pause.
• The fault code will flash on the red STOP lamp.
• There is a short one or two second pause between each number.

When the number has finished flashing in red, a amber WARNING lamp will appear again. The fault code will repeat the same sequence until cycling to the next active fault code.

When not using the diagnostic system, turn the diagnostic switch off, or remove the shorting plug.

The throttle activated diagnostic switch is intended to eliminate the need for a dash mounted diagnostic switch, which is used to activate the diagnostic mode to display active fault codes in a sequence of flashing lamps. The throttle activated diagnostic switch feature provides a simple sequence of throttle movements that activate the diagnostic mode.

When the engine is not running, the ignition switch is turned on, and the feature flag is enabled, a sequence of three throttle cycles will activate the diagnostic mode. The increment/decrement switch can be used to navigate to the next or previous fault code. In case these switches are not available, a throttle cycle will also increment to the next fault.

Additional fault code information can be obtained by using the INSITE™ electronic service tool. The snapshot data records the value or state of the control system sensors and switches at the time a fault code occurred. Either set of data is stored for the first occurrence of the fault, since it was last cleared, and for the most recent occurrence. This data can be very valuable when trying to recreate or determine engine operating conditions at the time of the fault.