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OBJECTIVES

OBJECTIVES. After studying Chapter 17, the reader will be able to: Prepare for ASE Engine Performance (A8) certification test content area “C” (Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair). Describe how to check an electric fuel pump for proper pressure and volume delivery.

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OBJECTIVES

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  1. OBJECTIVES After studying Chapter 17, the reader will be able to: • Prepare for ASE Engine Performance (A8) certification test content area “C” (Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair). • Describe how to check an electric fuel pump for proper pressure and volume delivery. • Explain how to check a fuel-pressure regulator. • Describe how to test fuel injectors. • Explain how to diagnose electronic fuel-injection problems.

  2. FUEL DELIVERY SYSTEM • Creating and maintaining a correct air-fuel mixture requires a properly functioning fuel and air delivery system. • Fuel delivery (and return) systems use many if not all of the following components to make certain that fuel is available under the right conditions to the fuel-injection system: • Fuel storage tank, filler neck, and gas cap • Fuel tank pressure sensor • Fuel pump • Fuel filter(s) • Fuel delivery lines and fuel rail • Fuel pressure regulator • Evaporative emission controls • Fuel return line

  3. FUEL TANKS • A vehicle fuel tank is made of corrosion-resistant steel or polyethylene plastic. • Some models, such as sport utility vehicles (SUVs) and light trucks, may have an auxiliary fuel tank. FIGURE 17-1 A typical fuel tank installation.

  4. FUEL TANKS • Tank Location and Mounting • Filler Tubes • Pressure-Vacuum Filler Cap • Fuel Pickup Tube • Tank Venting Requirements • Rollover Leakage Protection

  5. FUEL TANKS FIGURE 17-2 A three-piece filler tube assembly.

  6. FUEL TANKS FIGURE 17-3 A view of a typical filler tube with the fuel tank removed. Notice the ground strap used to help prevent the buildup of static electricity as the fuel flows into the plastic tank. The check ball looks exactly like a ping-pong ball.

  7. FUEL TANKS FIGURE 17-4 Vehicles equipped with onboard refueling vapor recovery usually have a reduced size fill tube.

  8. FUEL TANKS FIGURE 17-5 The fuel pickup tube is part of the fuel sender and pump assembly.

  9. FUEL TANKS FIGURE 17-6 On some vehicles equipped with an airflow sensor, a switch is used to energize the fuel pump. In the event of a collision, the switch opens and the fuel flow stops.

  10. FUEL TANKS FIGURE 17-7 Ford uses an inertia switch to turn off the electric fuel pump in an accident.

  11. FUEL LINES • Fuel and vapor lines made of steel, nylon tubing, or fuel-resistant rubber hoses connect the parts of the fuel system. • Fuel lines supply fuel to the throttle body or fuel rail. • They also return excess fuel and vapors to the tank. • Depending on their function, fuel and vapor lines may be either rigid or flexible. • Fuel lines must remain as cool as possible.

  12. FUEL LINES • Rigid Lines • Flexible Lines • Fuel Line Mounting • Fuel-Injection Lines and Clamps • Fuel-Injection Fittings and Nylon Lines • Fuel Line Layout

  13. FUEL LINES FIGURE 17-8 Fuel lines are routed along the frame or body and secured with clips.

  14. FUEL LINES FIGURE 17-9 Some Ford metal line connections use spring-locks and O-rings.

  15. FUEL LINES FIGURE 17-10 Ford spring-lock connectors require a special tool for disassembly.

  16. FUEL LINES FIGURE 17-11 Typical quick-connect service stops.

  17. ELECTRIC FUEL PUMPS • The electric fuel pump is a pusher unit. When the pump is mounted in the tank, the entire fuel supply line to the engine can be pressurized. • Because the fuel, when pressurized, has a higher boiling point, it is unlikely that vapor will form to interfere with fuel flow. FIGURE 17-12 A roller cell-type electric fuel pump.

  18. ELECTRIC FUEL PUMPS • Positive Displacement Pump • Hydrokinetic Flow Pump Design • Modular Fuel Sender Assembly • Electric Pump Control Circuits • Chrysler • General Motors • Fords • Pump Pulsation Dampening • Variable Speed Pumps

  19. ELECTRIC FUEL PUMPS FIGURE 17-13 The pumping action of an impeller or rotary vane pump.

  20. ELECTRIC FUEL PUMPS FIGURE 17-14 An exploded view of a gerotor electric fuel pump. The impeller draws fuel from the tank through the sock and into the gerotor pump area. The impeller is also used to expel any vapors that could be in the fuel.

  21. ELECTRIC FUEL PUMPS FIGURE 17-15 A cutaway view of a typical two-stage turbine electric fuel pump.

  22. ELECTRIC FUEL PUMPS FIGURE 17-16 A typical fuel pump model assembly, which includes the pickup strainer and fuel pump, as well as the fuel-pressure sensor and fuel level sensing unit.

  23. ELECTRIC FUEL PUMPS FIGURE 17-17 A schematic showing that an inertia switch is connected in series between the fuel pump relay and the fuel pump.

  24. ELECTRIC FUEL PUMPS FIGURE 17-18 A typical fuel pulsator used mostly with roller vanetype pumps to help even out the pulsation in pressure that can cause noise.

  25. FUEL FILTERS • Despite the care generally taken in refining, storing, and delivering gasoline, some impurities get into the automotive fuel system. • Fuel filters remove dirt, rust, water, and other contamination from the gasoline before it can reach the fuel injectors. • Most fuel filters are designed to filter particles that are 10 to 20 microns or larger in size. FIGURE 17-19 Many fuel pump modules contain a non-replaceable fuel filter.

  26. FUEL FILTERS FIGURE 17-20 Inline fuel filters are usually attached to the fuel line with screw clamps or threaded connections. The fuel filter must be installed in the proper direction or a restricted fuel flow can result.

  27. FUEL FILTERS FIGURE 17-21 The final filter, also called a filter basket, is the final filter in the fuel system.

  28. FUEL PUMP TESTING • Fuel pump testing includes many different tests and procedures. • Even though a fuel pump can pass one test, it does not mean that there is not a fuel pump problem. • Testing Fuel-Pump Pressure • Rest Pressure Test • Dynamic Pressure Test • Testing Fuel-Pump Volume

  29. FUEL PUMP TESTING FIGURE 17-22 (a) A funnel helps in hearing if the electric fuel pump inside the gas tank is working. (b) If the pump is not running, check the wiring and current flow before going through the process of dropping the fuel tank to remove the pump.

  30. FUEL PUMP TESTING FIGURE 17-23 Typical fuel-pressure test Schrader valve.

  31. FUEL PUMP TESTING FIGURE 17-24 A fuel-pressure gauge connected to the fuelpressure tap (Schrader valve) on a port fuel-injected V-6 engine.

  32. FUEL PUMP TESTING FIGURE 17-25 The fuel system should hold pressure if the system is leak free.

  33. FUEL PUMP TESTING FIGURE 17-26 Many older General Motors fuel-injected vehicles are equipped with a fuel-pump test connector. The operation of the fuel pump can be checked by connecting a 12-volt test light to the positive (+) terminal of the battery and the point of the test light to the test connector. Turn the ignition to on (engine off). The light should either go out or come on for 2 seconds. This is a simple test to see if the computer can control the fuel-pump relay.

  34. FUEL PUMP TESTING FIGURE 17-27 If the vacuum hose is removed from the fuel-pressure regulator when the engine is running, the fuel pressure should increase. If it does not increase, then the fuel pump is not capable of supplying adequate pressure or the fuel-pressure regulator is defective. If gasoline is visible in the vacuum hose, the regulator is leaking and should be replaced.

  35. THE FUELPRESSURE STETHOSCOPE TEST FIGURE 17-28 Fuel should be heard returning to the fuel tank at the fuel return line if the fuel pump and fuel-pressure regulator are functioning correctly.

  36. FUEL PUMP TESTING FIGURE 17-29 A fuel-pressure reading does not confirm that there is enough fuel volume for the engine to operate correctly.

  37. FUEL PUMP TESTING FIGURE 17-30 Measuring the volume of fuel flowing through the fuel-pressure regulator may not show the true volume capacity of the fuel pump.

  38. FUEL PUMP TESTING FIGURE 17-31 A nonrestricted (wide-open) fuel volume test using a fuel volume tester without the restriction of other components in the fuel system, such as the regulator.

  39. REMOVE THE BED TO SAVE TIME? • The electric fuel pump is easier to replace on many General Motors pickup trucks if the bed is removed. • Access to the top of the fuel tank, where the access hole is located, for the removal of the fuel tank sender unit and pump is restricted by the bottom of the pickup truck bed. • Rather than drop the tank, it is often much easier to use an engine hoist or a couple of other technicians to lift the bed from the frame after removing only a few fasteners. FIGURE 17-32 Removing the bed from a pickup truck makes gaining access to the fuel pump a lot easier.

  40. FUEL-PUMP CURRENT DRAW TEST • Another test that can and should be performed on a fuel pump is to measure the current draw in amperes. • This test is most often performed by connecting a digital multimeter set to read DC amperes and test the current draw. FIGURE 17-33 The hookup to test the current draw of the fuel pump on a General Motors vehicle that is equipped with a fuel-pump test lead (prime connector).

  41. FUEL-PUMP CURRENT DRAW TEST FIGURE 17-34 To test the current draw of a fuel pump on a Ford vehicle, connect the meter leads at either the relay or the inertia switch.

  42. FUEL-PUMP CURRENT DRAW TEST FIGURE 17-35 Hookup for testing fuel pump current draw on any vehicle equipped with a fuel pump relay.

  43. FUEL-PUMP CURRENT RAMPING • Current ramping means to observe the current (amperes) waveform. • By checking the current waveform of the fuel pump, possible problems can be detected. • To perform a current ramping test, the following test equipment is required: • Digital storage oscilloscope • Current probe FIGURE 17-36 A digital storage oscilloscope, such as this Fluke 98-Series II and a low-current clamp, are necessary tools to perform current ramping.

  44. FUEL-PUMP CURRENT RAMPING • Most electric fuel pumps can be tested at one of three locations: • Fuel-pump test lead (most 1981–1995 General Motors fuel-injected vehicles) • Fuel-pump relay (use a fused jumper wire for the probe) • Fuel-pump fuse (use a fused jumper wire for the probe) FIGURE 17-37 A low amp current probe can be connected anywhere in the fuel pump circuit that is the most convenient including: (a) at the fuse, (b) at the relay,(c) at the test connector or even the ground wire for the pump.

  45. FUEL-PUMP CURRENT RAMPING • Scope Set-Up • Current Draw • Motor Commutator Bars and RPM • Pump Motor Speed • Case Study #1:Good Fuel Pump Waveform • Case Study #2: Damaged Pump • Case Study #3:Good Pressure, Low Volume

  46. FUEL-PUMP CURRENT RAMPING FIGURE 17-38 A typical electric fuel-pump motor that uses triangleshaped commutator segments and horizontal brushes.

  47. FUEL-PUMP CURRENT RAMPING FIGURE 17-39 As the fuel pump motor rotates, it produces a current waveform, as shown, as the brushes pass over the commutator segments.

  48. FUEL-PUMP CURRENT RAMPING FIGURE 17-40 The speed of the fuel-pump motor can be determined by the time it takes the motor to make one revolution, as determined by looking for unique commutator segment patterns.

  49. FUEL-PUMP CURRENT RAMPING FIGURE 17-41 The RPM of a pump is determined by first locating unique humps in the voltage waveform. The time for one revolution is determined by counting the number of divisions between unique humps and then multiplying it by the time per division.

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