Fuel Metering System Component Description. Cadillac DeVille 2000

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 2000 🢒 DeVille 🢒 Engine 🢒 Engine Controls - 4.6L 🢒 Fuel Metering System Component Description

The fuel metering system consists of the following parts:

•	The fuel supply components (fuel tank, pump, pipes).

•	The fuel pump electrical circuit.

•	The fuel rail.

•	The fuel injectors.

•	The fuel pressure regulator.

•	The throttle body.

•	The idle air control (IAC) valve.

•	The throttle position (TP) sensor.

System Overview

The fuel tank stores the fuel supply. An electric fuel pump attaches to the fuel sender assembly inside the fuel tank. The fuel pump sends fuel through the fuel feed pipe and an in-line fuel filter to the fuel rail assembly. The pump provides fuel at a pressure greater than is needed by the injectors. The fuel pressure regulator, part of the fuel rail assembly, keeps fuel available to the injectors at a regulated pressure. A separate fuel return pipe returns the unused fuel to the fuel tank.

Fuel Pump Electrical Circuit

The fuel pump relay is located below the rear seat inside the rear electrical center. The fuel pump relay allows the fuel pump to be energized by the PCM. When the ignition is first turned On, the PCM energizes the fuel pump relay for two seconds. This allows the fuel pump to run for two seconds and build up fuel pressure for cranking. The PCM then waits for ignition reference pulses from the ignition coils. Once the PCM sees references pulses, the PCM energizes the relay to run the fuel pump.

Fuel Rail Assembly

The fuel rail consists of five parts:

•	The pipe that carries fuel to each injector.

•	The fuel pressure regulator.

•	The fuel pressure test port.

•	The fuel rail ground strap.

•	Eight individual fuel injectors.

The fuel rail is mounted on the intake manifold and distributes fuel to each cylinder through the individual injectors.

Fuel is delivered from the pump through the fuel feed pipe to the inlet port of the fuel rail pipe. From the fuel feed inlet, fuel is directed to the front rail pipe, then a crossover to the rear pipe, then through the rear rail pipe to the fuel pressure regulator. Fuel in excess of injector needs flows back through the pressure regulator assembly to the outlet port of the fuel rail. Fuel then flows through the fuel return pipe to the fuel tank to begin the cycle again.

A eight digit identification number is stamped on the fuel rail assembly. The model identification contains the Julian date, the year, and the shift. Refer to this model identification number if servicing or part replacement is required.

Fuel Injectors

The top-feed fuel injector assembly is a solenoid operated device, controlled by the PCM, that meters pressurized fuel to a single engine cylinder. The PCM energizes the injector solenoid, which opens a ball valve, allowing 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 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 Pressure Regulator


(1)	Regulator Assembly
(2)	Pressure Regulator Spring
(3)	O-Ring -- Backup
(4)	O-Ring -- Large
(5)	Filter Screen
(6)	Relief Valve
(7)	O-Ring -- Small

The fuel pressure regulator is a diaphragm-operated relief valve with fuel pump pressure on one side, and regulator spring pressure and intake manifold vacuum on the other side. The function of the regulator is to maintain a constant fuel pressure across the director spray plate under all operating conditions. The pressure regulator compensates for engine load by increasing fuel pressure as engine intake manifold vacuum drops. The pressure regulator is mounted on the fuel rail.

The cartridge regulator is serviced as a separate component. When servicing the fuel pressure regulator, insure that the back-up O-ring, large O-ring, filter screen, and small O-ring are properly placed on the pressure regulator.

With the ignition On, and engine Off (zero vacuum), system fuel pressure at the pressure test connection should be 284-325 kPa (41-47 psi). If the pressure regulator supplies fuel pressure which is too low or too high, a driveability condition will result.

Throttle Body Assembly

The throttle body assembly attaches to the intake manifold. The throttle body controls air flow into the engine, thereby controlling engine output. The vehicle operator opens the throttle valve within the throttle body through the accelerator controls. During engine idle, the throttle valves are almost closed. A fixed air bypass orifice and the idle air control (IAC) valve handle the air flow control. The throttle body also provides the location for mounting the throttle position (TP) sensor.

Idle Air Control (IAC) Valve


(1)	IAC Valve Assembly
(2)	Throttle Blade
(3)	Pintle

The purpose of the IAC valve is to control engine idle speed, while preventing stalls due to changes in engine load. The throttle blade when closed allows a small amount of air into the intake manifold. However, most of the air for closed throttle engine operation passes through the IAC valve, bypassing the throttle blade. By moving a conical valve known as a pintle in toward the seat (to decrease air flow), or out away from the seat (to increase air flow), a controlled amount of air can be bypassed. If engine speed is too low, more air is bypassed in order to increase RPM. If engine speed is too high, less air is bypassed in order to decrease RPM. The PCM moves the IAC valve in small steps, called counts. These can be measured and displayed with a scan tool, which plugs into the data link connector (DLC). The PCM calculates the proper position of the IAC valve during idle based upon the battery voltage, the coolant temperature, the engine load, and the engine RPM. If the RPM drops below specification and the throttle valve is closed, the PCM senses a near stall condition and calculates a new valve position in order to prevent stalling.

•	Engine idle speed is a function of total air flow into the engine. Idle speed is based on IAC valve pintle position, crankcase ventilation valve flow, throttle valve opening, bypass orifice air flow, and calibrated vacuum loss through accessories.

•	Controlled idle speed is programmed into the PCM, which determines the correct IAC valve pintle position to maintain the desired idle speed for all engine operating conditions and loads.

•	The minimum idle air rate is set at the factory with a stop screw. This setting allows enough air flow by the throttle valve to cause the IAC valve pintle to be positioned a calibrated number of steps (counts), from the seat, during controlled idle operation.

If the IAC valve is disconnected or disabled with the engine running, the PCM may loose track of the IAC valve position causing erratic or incorrect idle speed. If this occurs, reset the IAC valve by doing the following:

Start and idle the engine foe 15 seconds.
Turn the ignition switch to the LOCK/OFF position.
Wait 15 seconds.
Restart the engine and inspect for proper idle operation.

Throttle Position (TP) Sensor

The TP sensor is a potentiometer that is mounted on the throttle body and provides the PCM with information on throttle valve angle. The PCM provides a 5 volt reference signal and a ground to the TP sensor and the sensor returns a signal voltage that changes with throttle valve angle. At closed throttle (close to 0 degrees) the TP sensor output signal is low (below 1 volt) and at WOT (greater than 80 degrees) the TP sensor output signal is high (above 4 volts). Because the TP sensor is not adjustable, the PCM must account for build tolerances that could affect the TP sensor output at closed throttle. The PCM uses a learning algorithm so that it can correct for variations of up to 6 degrees of throttle angle.

The PCM uses TP information to modify fuel control based on throttle valve angle. For example, power enrichment occurs when the throttle angle approaches WOT. Acceleration enrichment occurs when the throttle angle increases rapidly (similar to an accelerator pump on a carburetor). A faulty TP sensor may cause various driveability conditions and should set a DTC.

Accelerator Controls

The accelerator control system is cable type. There are no linkage adjustments. Therefore, the specific cable for each application must be used. The accelerator cable is routed through the groove in the throttle body lever.


(1)	Accelerator Control Cable
(2)	Accelerator Pedal Assembly
(3)	Accelerator Pedal Retainer

Accelerator Controls Cable - Export


(1)	Accelerator Controls Cable - Export

Accelerator Controls Pedal - Export


(1)	Accelerator Controls Cable - Export
(2)	Accelerator Controls Pedal Nuts - Export
(3)	Accelerator Controls Pedal - Export

When work has been performed on accelerator controls, always make sure that all components are installed correctly and that linkage and cables are not rubbing or binding in any manner. The throttle should operate freely without bind between full closed and wide open throttle.