AT 261 – Lab 10b - Return Based - Fuel Systems – Injectors, Pumps, Pressure Regulators, Filters, and LinesName: _________________________________________ Group: _____________________Date: __________________________________________How Electronic Fuel Injection (EFI) Works;The fuel delivery system consists of the fuel tank, fuel pump, fuel filter, fuel injector, pressure regulator, and a fuel return line.Fuel is delivered from the tank to the injectors by means of an electric fuel pump that is controlled by a relay. The fuel pump relay is controlled by the Powertrain Control Module (PCM/ECM/ECU).Fuel pressure is maintained at a constant pressure by means of a fuel pressure regulator. Any fuel, which is not delivered into the injectors, is sent back to the fuel tank through the fuel return line.The PCM is in direct control of the fuel injectors. While the fuel pressure regulator is controlled by air pressure in the air intake. The amount of fuel that passes through the injectors is controlled by the PCM by controlling the “on/off” timing of the injector. This timing is known as “Pulse Width”.Fuel Control and AdjustmentsThe PCM reads data from various sensors measuring temperatures (ECT/IAT), throttle angle (TPS), air pressures (MAP/BP/MAF), and mixture ratio (HO2S). The PCM determines precisely how much fuel is needed at any given time.Air enters the engine through the air intake system and is measured either by atmospheric pressure (MAP/BP), or by its mass and volume (MAF). As the air flows into the cylinder it is mixed with fuel from the injector.Each fuel injector is arranged behind the intake valve of each cylinder. The fuel injector is a solenoid, and is controlled by the PCM.The PCM pulses the injectors on or off by turning each injectors ground circuit on or off (The PCM acts as a ground side switch).When the injector is turned on it opens spraying atomized fuel at the backside of the intake valve.As fuel is sprayed into the intake air stream it mixes with the incoming air pressures and vaporizes due to low pressures on the intake valve in the intake manifold. The PCM signals the injectors to deliver just enough fuel to achieve an ideal air/fuel ratio of 14.7:1.Advantages of EFIUniform Air/Fuel Mixture Distribution – Each cylinder has its own injector, which delivers the fuel directly to the intake valve. Thiseliminates the need for fuel to travel through the entire intake manifold (like a carburetor/TBI system), improving cylinder distribution.Highly Accurate Air/Fuel Control Throughout All Engine Operating Conditions – EFI supplies a constantly accurate air/fuel mixture to the engine no matter what operating conditions are encountered. This provides better driveability, fuel economy and emissions.Superior Throttle Response and Power - By delivering the fuel directly to the backside of the intake valve, the intake manifold design can be optimized to improve air velocity at the intake valve. This improves torque and throttle response.Simpler Mechanics – The EFI system does not rely on any major mechanical adjustments for cold starting or fuel metering. Because the system is mechanically simple (very few moving parts) maintenance requirements are reduced.Excellent Fuel Economy with Improved Emissions Control – Cold engine and wide-open throttle (WOT) enrichment and be reduced with EFI. Fuel does not “puddle” in the intake runners since fuel is delivered directly to the intake valve.Improved Cold Engine Startability and Operation – The combination of better fuel atomization and injection directly at the intake valve improves the ability to start and run a cold engine.(Continued Onto the Next Page..)1Injector Testing, Pressure Regulator Testing, and Pump Testing.Tools needed;Fuel pressure test kit, Noid lights, DVOM, Tool board, and Fused Jumper wiresLook in Mitchell's under section for Specifications or Basic TestingsYou will need – Fuel Pressure Testing, Fuel Pressure Data, Injector Testing (ohms)Make ________________ Model ________________ Year ________________ Engine Size and Type ______ Perform a complete visual inspection on your fuel system. Do you see any problems? _______________________________________________________Step 1 – Testing Fuel Pressure and Regulator Operation Install a fuel pressure test gauge to your vehicle, if needed bleed down the fuel pressure in order to install the fuel pressure test gauge. Turn the ignition key to the on position DO NOT start the vehicle. What happened to the fuel pressure? ___________________This is the prime pulse that pressurizes the fuel system for a start procedure, if you do not see prime pulse chances are the fuel system is inoperative. What is the specified fuel pressure KOER (key on, engine running) for your vehicle? ________________ PSI Start the engine, allow the engine to idle, and monitor the fuel pressure. Is the fuel pressure within spec? (Yes/No) ______________________, Fuel Pressure Is - ________________ PSIIf fuel pressure were low, this would indicate a weak pump, a clogged filter, or a restricted pressure line. If fuel pressure ishigh this would indicate a restriction in the return line back to the fuel pump. With the engine still running, momentarily disconnect the vacuum line to the fuel pressure regulator.  If raw fuel comes out of the fuel pressure regulator, this would indicate a bad diaphragm in the regulator, this unburned fuel would then get pulled into the intake and cause a rich running condition. Black smoke, fuel-diluted oil, and low fuel economy would be the result of this condition. With the vacuum line disconnected, what is your reading now? _____________________ PSI Reconnect the fuel pressure regulator vacuum line and now rev the engine to about 2000 RPM several times in a row.  What happens to your fuel pressure reading? _______________ Momentary perform a WOT - monitor the fuel pressure as you reach WOT.  What happens to the fuel pressure at WOT? ___________________ PSIThus we can conclude that when engine vacuum is high (idle, decel) fuelpressure is low, and when engine vacuum is low (WOT, accelerate), fuelpressure is high. This is done to overcome the pressure change in the intakemanifold, to keep the fuel supply constant during all engine-operating conditions. NOTE: If fuel pressure does not change it would indicate a bad vacuum line(disconnected or clogged) to the pressure regulator,