Halderman ch077 lecture


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Halderman ch077 lecture

  2. 2. Objectives <ul><li>The student should be able to: </li></ul><ul><ul><li>Prepare for ASE Engine Performance (A8) certification test content area “C” (Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair). </li></ul></ul><ul><ul><li>Discuss fuel tanks, lines and filters. </li></ul></ul><ul><ul><li>Describe how fuel pumps work. </li></ul></ul><ul><ul><li>Describe how to check an electric fuel pump for proper pressure and volume delivery. </li></ul></ul>
  3. 3. Objectives <ul><li>The student should be able to: </li></ul><ul><ul><li>Explain how to check a fuel-pressure regulator. </li></ul></ul><ul><ul><li>Describe how to test fuel injectors. </li></ul></ul><ul><ul><li>Explain how to diagnose electronic fuel-injection problems. </li></ul></ul>
  5. 5. Fuel Delivery System <ul><li>Fuel delivery systems use the following components: </li></ul><ul><ul><li>Fuel storage tank, filler neck, and gas cap </li></ul></ul><ul><ul><li>Fuel tank pressure sensor </li></ul></ul>
  6. 6. Fuel Delivery System <ul><li>Fuel delivery systems use the following components: </li></ul><ul><ul><li>Fuel pump </li></ul></ul><ul><ul><li>Fuel filter(s) </li></ul></ul>
  7. 7. Fuel Delivery System <ul><li>Fuel delivery systems use the following components: </li></ul><ul><ul><li>Fuel delivery lines and fuel rail </li></ul></ul><ul><ul><li>Fuel-pressure regulator </li></ul></ul><ul><ul><li>Fuel return line (if equipped with a return-type fuel delivery system) </li></ul></ul>
  8. 8. FUEL TANKS
  9. 9. Fuel Tanks <ul><li>Vehicle fuel tank is made of corrosion-resistant steel or polyethylene plastic </li></ul><ul><li>Some models may have auxiliary tank </li></ul><ul><li>Tank design and capacity are compromise between the following: </li></ul><ul><ul><li>Space </li></ul></ul>
  10. 10. Fuel Tanks <ul><li>Tank design and capacity are compromise between the following: </li></ul><ul><ul><li>Filler location </li></ul></ul><ul><ul><li>Fuel expansion room </li></ul></ul><ul><ul><li>Fuel movement </li></ul></ul>
  11. 11. Fuel Tanks <ul><li>Vertical baffle in fuel tanks limit fuel sloshing </li></ul>
  12. 12. Figure 77-1 A typical fuel tank installation.
  13. 13. Fuel Tanks <ul><li>Fuel tanks include these features: </li></ul><ul><ul><li>Inlet or filler tube through which fuel enters the tank </li></ul></ul><ul><ul><li>Filler cap with pressure holding and relief features </li></ul></ul>
  14. 14. Fuel Tanks <ul><li>Fuel tanks include these features: </li></ul><ul><ul><li>An outlet to the fuel line leading to the fuel pump or fuel injector </li></ul></ul><ul><ul><li>Fuel pump mounted within the tank </li></ul></ul>
  15. 15. Fuel Tanks <ul><li>Fuel tanks include these features: </li></ul><ul><ul><li>Tank vent system </li></ul></ul><ul><ul><li>Fuel pickup tube and fuel level sending unit </li></ul></ul>
  16. 16. Fuel Tanks <ul><li>Tank Location and Mounting </li></ul><ul><ul><li>Horizontally suspended fuel tank </li></ul></ul><ul><ul><li>Usually mounted below rear floor pan before or behind rear axle </li></ul></ul>
  17. 17. Fuel Tanks <ul><li>Tank Location and Mounting </li></ul><ul><ul><li>Body components protect tank in case of collision </li></ul></ul><ul><ul><li>Insulated strips often cemented to tank wherever it contacts underbody to prevent squeaks </li></ul></ul>
  18. 18. Fuel Tanks <ul><li>Tank Location and Mounting </li></ul><ul><ul><li>Fuel inlet located behind filler cap </li></ul></ul><ul><ul><li>Pair of metal retaining straps usually hold tank in place </li></ul></ul>
  19. 19. Fuel Tanks <ul><li>Filler Tubes </li></ul><ul><ul><li>Fuel enters tank though large tube extending from tank to opening outside vehicle </li></ul></ul>
  20. 20. Figure 77-2 A three-piece filler tube assembly. The main three parts include the upper neck, hose, and lower neck.
  21. 21. Fuel Tanks <ul><li>Filler Tubes </li></ul><ul><ul><li>Since 1993, regulations require device to prevent fuel siphoning from tank </li></ul></ul><ul><ul><li>Filler-neck check-ball tube was added to fuel tanks </li></ul></ul>
  22. 22. Fuel Tanks <ul><li>Filler Tubes </li></ul><ul><ul><li>To drain check-ball-equipped fuel tanks, disconnect check-ball tube at tank and attach siphon directly to tank </li></ul></ul>
  23. 23. Figure 77-3 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.
  24. 24. Fuel Tanks <ul><li>Filler Tubes </li></ul><ul><ul><li>Onboard refueling vapor recovery (ORVR) systems reduce evaporative emissions during refueling </li></ul></ul><ul><ul><li>ORVR systems adds components to filler neck and tank </li></ul></ul>
  25. 25. Figure 77-4 Vehicles equipped with onboard refueling vapor recovery usually have a reduced-size fill tube.
  26. 26. Fuel Tanks <ul><li>Pressure-Vacuum Filler Cap </li></ul><ul><ul><li>Fuel and vapors are sealed in tank by safety filler cap </li></ul></ul><ul><ul><li>Safety cap must release excess pressure and vacuum </li></ul></ul>
  27. 27. Fuel Tanks <ul><li>Pressure-Vacuum Filler Cap </li></ul><ul><ul><li>Either condition can cause tank damage, spills, and vapor escape </li></ul></ul><ul><ul><li>Cap will release pressure over 1.5 to 2.0 PSI (10 to 14 kPa) </li></ul></ul><ul><ul><li>Cap will release vacuum if it is 0.15 to 0.30 PSI (1 to 2 kPa) </li></ul></ul>
  28. 28. Fuel Tanks <ul><li>Fuel Pickup Tube </li></ul><ul><ul><li>Fuel pickup tube is part of fuel sender assembly or electric fuel pump assembly </li></ul></ul><ul><ul><li>Fuel pickup tube is fitted with filter to prevent contamination from entering fuel lines </li></ul></ul>
  29. 29. Figure 77-5 The fuel pickup tube is part of the fuel sender and pump assembly.
  30. 30. Fuel Tanks <ul><li>Fuel Pickup Tube </li></ul><ul><ul><li>Filter is made from woven Saran resin </li></ul></ul><ul><ul><li>Filter blocks water in tank </li></ul></ul><ul><ul><li>Filter should be replaced when fuel pump is replaced </li></ul></ul>
  31. 31. Fuel Tanks <ul><li>Tank Venting Requirements </li></ul><ul><ul><li>Vents required to prevent vacuum lock as fuel is drawn from tank </li></ul></ul><ul><ul><li>Venting tank allows outside air to enter as fuel level drops </li></ul></ul>
  32. 32. Fuel Tanks <ul><li>Tank Venting Requirements </li></ul><ul><ul><li>EVAP system vents gasoline vapors from tank to charcoal-filled vapor storage canister </li></ul></ul><ul><ul><li>Storage canister has unvented filler cap </li></ul></ul>
  33. 33. Fuel Tanks <ul><li>Tank Venting Requirements </li></ul><ul><ul><li>Many filler caps contain valves that open to relieve pressure or vacuum </li></ul></ul><ul><ul><li>Tanks must allow for fuel expansion, contraction, and overflow due to changes in temperature and overfilling </li></ul></ul>
  34. 34. Fuel Tanks <ul><li>Tank Venting Requirements </li></ul><ul><ul><li>Some tanks feature tank with dome at top </li></ul></ul><ul><ul><li>Dome reserves up to 12% of tank capacity for fuel expansion </li></ul></ul>
  36. 36. Rollover Leakage Protection <ul><li>All vehicles have one or more devices to prevent fuel leaks in case of vehicle rollover or collision </li></ul>
  37. 37. Rollover Leakage Protection <ul><li>Devices to prevent leaks include: </li></ul><ul><ul><li>Check valves </li></ul></ul><ul><ul><li>Fuel pump shut off devices </li></ul></ul><ul><ul><li>Inertia switches </li></ul></ul>
  38. 38. Figure 77-6 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.
  39. 39. Figure 77-7 Ford uses an inertia switch to turn off the electric fuel pump in an accident.
  40. 40. FUEL LINES
  41. 41. Fuel Lines <ul><li>Fuel and vapor lines made of steel, nylon tubing, or fuel-resistant rubber </li></ul><ul><li>May be rigid or flexible depending on function </li></ul><ul><li>Must remain as cool as possible </li></ul>
  42. 42. Fuel Lines <ul><li>If located near heat source, gasoline may vaporize and cause vapor lock </li></ul><ul><li>Vapor lock causes engine to stall and hot restart problem develops </li></ul><ul><li>Some fuel system components require fuel to be delivered at up to 35 PSI (241 kPa) </li></ul>
  43. 43. Fuel Lines <ul><li>Fuel-injection systems retain residual pressure in lines for a half hour to prevent hot engine restart problems </li></ul><ul><li>Special fuel lines required to withstand these pressures </li></ul>
  44. 44. Fuel Lines <ul><li>Rigid Lines </li></ul><ul><ul><li>Fuel lines fastened to body, frame, or engine made of nylon reinforced plastic or seamless steel tubing </li></ul></ul>
  45. 45. Fuel Lines <ul><li>Rigid Lines </li></ul><ul><ul><li>Use only steel tubing when replacing rigid fuel lines </li></ul></ul><ul><ul><li>Never substitute copper or aluminum tubing for steel tubing </li></ul></ul>
  46. 46. Fuel Lines <ul><li>Flexible Lines </li></ul><ul><ul><li>Most fuel systems use synthetic rubber hose where flexibility is needed </li></ul></ul><ul><ul><li>Lines often connect steel fuel lines to other components </li></ul></ul>
  47. 47. Fuel Lines <ul><li>Flexible Lines </li></ul><ul><ul><li>Delivery hose inside diameter is usually 3/16” or 3/8” (8 or 10 mm) </li></ul></ul><ul><ul><li>Return line is normally 1/4” (6 mm) </li></ul></ul>
  48. 48. Fuel Lines <ul><li>Flexible Lines </li></ul><ul><ul><li>Fuel-injection systems require hoses suitable for higher-pressure systems </li></ul></ul><ul><ul><li>Vapor vent lines require materials that resist fuel vapors </li></ul></ul>
  49. 49. Fuel Lines <ul><li>Fuel Line Mounting </li></ul><ul><ul><li>Fuel supply lines normally routed to follow frame along vehicle underbody </li></ul></ul><ul><ul><li>Vapor and return lines may be routed with fuel supply line </li></ul></ul><ul><ul><li>Rigid lines fastened to frame rail or underbody with screws, clamps, clips </li></ul></ul>
  50. 50. Figure 77-8 Fuel lines are routed along the frame or body and secured with clips.
  51. 51. Fuel Lines <ul><li>Fuel-Injection Lines and Clamps </li></ul><ul><ul><li>Hoses for fuel-injection systems made from materials with high resistance to oxidation and deterioration </li></ul></ul>
  52. 52. Fuel Lines <ul><li>Fuel-Injection Lines and Clamps </li></ul><ul><ul><li>Replacement hoses should always be equivalent to OEM hoses </li></ul></ul><ul><ul><li>Screw-type clamps are essential for injected engines </li></ul></ul>
  53. 53. Fuel Lines <ul><li>Fuel-Injection Lines and Clamps </li></ul><ul><ul><li>Clamps should have rolled edges to prevent hose damage </li></ul></ul><ul><ul><li>CAUTION: Do not use spring-type clamps on fuel-injected engines—they cannot withstand the fuel pressures involved. </li></ul></ul>
  54. 54. Fuel Lines <ul><li>Fuel-Injection Fittings and Nylon Lines </li></ul><ul><ul><li>Fittings and lines for fuel injection engines are subject to high pressures </li></ul></ul><ul><ul><li>Special lines and fittings used to ensure against leaks </li></ul></ul>
  55. 55. Fuel Lines <ul><li>Fuel-Injection Fittings and Nylon Lines </li></ul><ul><ul><li>Some fittings on GM vehicles use O-ring seals instead of flare connections </li></ul></ul><ul><ul><li>Tighten O-ring fittings to specified torque value </li></ul></ul>
  56. 56. Fuel Lines <ul><li>Fuel-Injection Fittings and Nylon Lines </li></ul><ul><ul><li>Replace O-rings when fuel system connection is opened </li></ul></ul><ul><ul><li>Ford uses spring-lock connectors to join male and female ends of steel tubing </li></ul></ul>
  57. 57. Figure 77-9 Some Ford metal line connections use springlocks and O-rings.
  58. 58. Fuel Lines <ul><li>GM has used nylon fuel lines with quick-connect fittings at fuel tank and fuel filter </li></ul><ul><li>Unlocking metal quick-connector requires separator tool </li></ul>
  59. 59. Figure 77-10 Ford spring-lock connectors require a special tool for disassembly.
  60. 60. Figure 77-11 Typical quick-connect steps.
  61. 61. Fuel Lines <ul><li>Fuel Line Layout </li></ul><ul><ul><li>Fuel pressures have become higher to prevent vapor lock </li></ul></ul><ul><ul><li>Major portion of fuel returns to tank through fuel return line </li></ul></ul>
  62. 62. Fuel Lines <ul><li>Fuel Line Layout </li></ul><ul><ul><li>Allows better control of heat absorbed by gasoline as it is routed through engine compartment </li></ul></ul>
  63. 63. Fuel Lines <ul><li>Fuel Line Layout </li></ul><ul><ul><li>Warmer fuel in tank may cause excessive rise in pressure in tank </li></ul></ul><ul><ul><li>Manufacturers have installed pressure regulator by tank </li></ul></ul>?
  65. 65. Electric Fuel Pumps <ul><li>Electric fuel pump is pusher unit </li></ul><ul><li>When pump is mounted in tank, entire fuel supply line can be pressurized </li></ul><ul><li>Pressurized fuel has higher boiling point so vapor is less likely to form and interfere with fuel flow </li></ul>
  66. 66. Electric Fuel Pumps <ul><li>Most vehicles use impeller or turbine pumps </li></ul><ul><li>All pumps are driven by electric motor </li></ul><ul><li>Turbine pumps turn at higher speeds and are quieter </li></ul>?
  67. 67. Figure 77-12 A roller cell-type electric fuel pump.
  68. 68. Electric Fuel Pumps <ul><li>Positive Displacement Pump </li></ul><ul><ul><li>Positive replacement pump forces everything that enters pump to leave pump </li></ul></ul><ul><ul><li>Roller cell or vane pump draws fuel into pump </li></ul></ul>
  69. 69. Electric Fuel Pumps <ul><li>Positive Displacement Pump </li></ul><ul><ul><li>Fuel is pushed out through fuel line to injection system </li></ul></ul><ul><ul><li>All pumps use variable-sized chamber to draw in fuel </li></ul></ul>
  70. 70. Electric Fuel Pumps <ul><li>Positive Displacement Pump </li></ul><ul><ul><li>When maximum volume has been drawn in supply port closes </li></ul></ul><ul><ul><li>Discharge opens and fuel is forced out </li></ul></ul>
  71. 71. Electric Fuel Pumps <ul><li>Positive Displacement Pump </li></ul><ul><ul><li>Chambers are formed by rollers and gears in a rotor plate </li></ul></ul><ul><ul><li>Pump has no valves, so fuel flows steadily through entire pump housing </li></ul></ul>
  72. 72. Electric Fuel Pumps <ul><li>Positive Displacement Pump </li></ul><ul><ul><li>Only when vehicle runs out of fuel is there risk of pump damage </li></ul></ul><ul><ul><li>Most electric fuel pumps have fuel outlet check valve </li></ul></ul>
  73. 73. Electric Fuel Pumps <ul><li>Positive Displacement Pump </li></ul><ul><ul><li>Check valve closes to maintain fuel pressure when pump shuts off </li></ul></ul><ul><ul><li>Residual pressure prevents vapor lock and hot-start problems </li></ul></ul>
  74. 74. Electric Fuel Pumps <ul><li>Positive Displacement Pump </li></ul><ul><ul><li>Rotary vane pump consists of these parts: </li></ul></ul><ul><ul><ul><li>Central impeller disk </li></ul></ul></ul><ul><ul><ul><li>Several rollers or vanes </li></ul></ul></ul><ul><ul><ul><li>Pump housing </li></ul></ul></ul>
  75. 75. Figure 77-13 The pumping action of an impeller or rotary vane pump.
  76. 76. Electric Fuel Pumps <ul><li>Positive Displacement Pump </li></ul><ul><ul><li>Unpressurized fuel enters pump </li></ul></ul><ul><ul><li>Fuel fills space between rollers and is trapped between impeller, housing, and roller </li></ul></ul><ul><ul><li>Meshing of gear teeth pressurize fuel </li></ul></ul>
  77. 77. Figure 77-14 An exploded view of a gerotor electric fuel pump.
  78. 78. Electric Fuel Pumps <ul><li>Hydrokinetic Flow Pump Design </li></ul><ul><ul><li>Moves fuel rapidly to create pressure </li></ul></ul><ul><ul><li>Turbine pump is less noisy </li></ul></ul><ul><ul><li>Uses impeller that accelerates fuel before discharging it </li></ul></ul>
  79. 79. Figure 77-15 A cutaway view of a typical two-stage turbine electric fuel pump.
  80. 80. Electric Fuel Pumps <ul><li>Hydrokinetic Flow Pump Design </li></ul><ul><ul><li>Turbine pump has staggered blade design to minimize noise </li></ul></ul><ul><ul><li>Staggered blade separates vapor from liquid fuel </li></ul></ul>
  81. 81. Electric Fuel Pumps <ul><li>Hydrokinetic Flow Pump Design </li></ul><ul><ul><li>After fuel passes strainer, it is pressurized and delivered into fuel feed pipe </li></ul></ul><ul><ul><li>Typical electric fuel pump delivers 40 to 50 gallons per hour </li></ul></ul><ul><ul><li>Produces pressure of 70 to 90 PSI </li></ul></ul>
  82. 82. Electric Fuel Pumps <ul><li>Modular Fuel Sender Assembly </li></ul><ul><ul><li>Modular fuel sender consists of fuel level sensor, turbine pump, and jet pump </li></ul></ul><ul><ul><li>Fuel transferred from pump to fuel pipe through convoluted fuel pipe </li></ul></ul>
  83. 83. Electric Fuel Pumps <ul><li>Modular Fuel Sender Assembly </li></ul><ul><ul><li>Convoluted pipe eliminates need for rubber hoses, nylon pipes, and clamps </li></ul></ul><ul><ul><li>Reservoir dampens fuel slosh to maintain constant fuel level </li></ul></ul>?
  84. 84. Electric Fuel Pumps <ul><li>Electric Pump Control Circuits </li></ul><ul><ul><li>Fuel pump circuits are controlled by fuel pump relay </li></ul></ul><ul><ul><li>Fuel pump relays are activated by turning ignition key to on </li></ul></ul>
  85. 85. Electric Fuel Pumps <ul><li>Electric Pump Control Circuits </li></ul><ul><ul><li>Fuel pump then pressurizes fuel system </li></ul></ul><ul><ul><li>For safety reasons, relay de-energizes after few seconds until key is moved to crank </li></ul></ul>
  86. 86. Electric Fuel Pumps <ul><li>Electric Pump Control Circuits </li></ul><ul><ul><li>Once engine is rotating, relay remains energized </li></ul></ul><ul><ul><li>On Chrysler vehicles, PCM must receive engine speed signal before it can energize fuel pump </li></ul></ul>
  87. 87. Electric Fuel Pumps <ul><li>Electric Pump Control Circuits </li></ul><ul><ul><li>GM systems energize pump with ignition switch but then deactivates pump if RPM signal is not received </li></ul></ul><ul><ul><li>Most Ford vehicles have inertia switch between fuel pump relay and pump </li></ul></ul>
  88. 88. Electric Fuel Pumps <ul><li>Electric Pump Control Circuits </li></ul><ul><ul><li>Fuel pump energizes </li></ul></ul><ul><ul><li>If RPM signal is not received by PCM within one second, fuel pump is de-energized </li></ul></ul>
  89. 89. Figure 77-17 A schematic showing that an inertia switch is connected in series between the fuel-pump relay and the fuel pump.
  90. 90. Electric Fuel Pumps <ul><li>Pump Pulsation Dampening </li></ul><ul><ul><li>Some manufacturers use accumulator to reduce pressure pulses and noise </li></ul></ul><ul><ul><li>Others use pulsator located at outlet of fuel pump to absorb pressure pulsations created by pump </li></ul></ul>
  91. 91. Electric Fuel Pumps <ul><li>Pump Pulsation Dampening </li></ul><ul><ul><li>Pulsators usually used on roller vane pumps and are source of many internal fuel leaks </li></ul></ul>
  92. 92. Electric Fuel Pumps <ul><li>Pump Pulsation Dampening </li></ul><ul><ul><li>NOTE: Some experts suggest that the pulsator be removed and replaced with a standard section of fuel line to prevent the loss of fuel pressure that results when the connections on the pulsator loosen and leak fuel back into the tank. </li></ul></ul>
  93. 93. Figure 77-18 A typical fuel pulsator used mostly with roller vane-type pumps to help even out the pulsation in pressure that can cause noise.
  94. 94. Electric Fuel Pumps <ul><li>Variable Speed Pumps </li></ul><ul><ul><li>Another way to reduce noise, current draw, and pump wear is to reduce speed of pump when less than maximum output is needed </li></ul></ul><ul><ul><li>Pump speed and pressure can be regulated by controlling voltage supplied </li></ul></ul>
  95. 95. Electric Fuel Pumps <ul><li>Variable Speed Pumps </li></ul><ul><ul><li>Controlling voltage can be done with resistor switched into circuit </li></ul></ul><ul><ul><li>Voltage can be controlled by letting the engine control computer pulse-width modulate the voltage supply </li></ul></ul><ul><ul><li>Slower pump speed and pressure produces less noise </li></ul></ul>
  96. 96. FUEL FILTERS
  97. 97. Fuel Filters <ul><li>Remove dirt, rust, water, and other contaminants </li></ul><ul><ul><li>Most filters remove particles 10 to 20 microns in size or larger </li></ul></ul><ul><li>Some fuel systems may contain two or more filters </li></ul>
  98. 98. Fuel Filters <ul><li>Inline filter is located between fuel pump and throttle body or fuel rail </li></ul><ul><ul><li>Inline fuel filter protects system from contamination </li></ul></ul><ul><ul><li>Inline filter does not protect fuel pump </li></ul></ul>
  99. 99. Fuel Filters <ul><li>Filters should be replaced according to manufacturer’s recommendations </li></ul><ul><ul><li>Usual range is every 30,000 miles (48,000 km) to 100,000 miles (160,000 km) </li></ul></ul><ul><li>Fuel filters that are part of fuel pump module usually do not have specified service interval </li></ul>
  100. 100. Figure 77-19 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.
  102. 102. Fuel-Pump Testing <ul><li>Many different fuel-pump tests and procedures </li></ul><ul><li>Pump may pass one test but still have problem </li></ul><ul><li>Example: Pump motor rotates slower than normal </li></ul>
  103. 103. Fuel-Pump Testing <ul><li>Pump may produce enough pressure, but not enough volume </li></ul><ul><li>Testing Fuel-Pump Pressure </li></ul><ul><ul><li>Fuel pump pressure important because of requirement for exact fuel control </li></ul></ul>
  104. 104. Fuel-Pump Testing <ul><li>Testing Fuel-Pump Pressure </li></ul><ul><ul><li>Most fuel-injection systems operate at low pressure of about 10 PSI or high pressure between 35 and 45 PSI </li></ul></ul>
  105. 105. Fuel-Pump Testing
  106. 106. Fuel-Pump Testing <ul><li>In both systems, maximum fuel-pump pressure is about double normal operating pressure to ensure continuous flow of cool fuel </li></ul><ul><li>To measure fuel-pump pressure, locate Schrader valve </li></ul><ul><li>Attach fuel-pressure gauge </li></ul>
  107. 107. Fuel-Pump Testing <ul><li>NOTE: Some vehicles, such as those with General Motors TBI fuel-injection systems require a specific fuel-pressure gauge that connects to the fuel system. Always follow the manufacturer’s recommendations and procedures. </li></ul>
  108. 108. Figure 77-22 The Schrader valve on this General Motors 3800 V-6 is located next to the fuel-pressure regulator.
  109. 109. Fuel-Pump Testing <ul><li>Rest Pressure Test </li></ul><ul><ul><li>If fuel pressure is acceptable, check system for leakdown </li></ul></ul><ul><ul><li>Observe pressure gauge after five minutes </li></ul></ul>
  110. 110. Fuel-Pump Testing <ul><li>Rest Pressure Test </li></ul><ul><ul><li>Pressure should be the same as initial reading </li></ul></ul><ul><ul><li>If not, the pressure regulator, fuel-pump check valve, or injectors are leaking </li></ul></ul>
  111. 111. Figure 77-23 The fuel system should hold pressure if the system is leak free.
  112. 112. Fuel-Pump Testing <ul><li>Dynamic Pressure Test </li></ul><ul><ul><li>Start the engine </li></ul></ul><ul><ul><li>If pressure is vacuum referenced, pressure should change when throttle is cycled </li></ul></ul>
  113. 113. Fuel-Pump Testing <ul><li>Dynamic Pressure Test </li></ul><ul><ul><li>If pressure doesn’t change, check vacuum supply circuit </li></ul></ul><ul><ul><li>Remove vacuum line from regulator and inspect for presence of fuel </li></ul></ul>
  114. 114. Fuel-Pump Testing <ul><li>Dynamic Pressure Test </li></ul><ul><ul><li>There should never be fuel present on vacuum side of regulator diaphragm </li></ul></ul><ul><ul><li>When engine speed increases, pressure should remain within specifications </li></ul></ul>
  115. 115. Figure 77-24 If the vacuum hose is removed from the fuelpressure 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.
  116. 116. Fuel-Pump Testing <ul><li>Dynamic Pressure Test </li></ul><ul><ul><li>Some engines do not have vacuum-referenced regulator </li></ul></ul><ul><ul><li>Running pressure should remain constant </li></ul></ul><ul><ul><li>Pressure will be higher than on return-type systems </li></ul></ul>
  117. 117. Fuel-Pump Testing <ul><li>Testing Fuel-Pump Volume </li></ul><ul><ul><li>Sufficient fuel capacity (flow) should be at least 2 pints (1 liter) every 30 seconds, or 1 pint in 15 seconds </li></ul></ul>
  118. 118. Fuel-Pump Testing <ul><li>Testing Fuel-Pump Volume </li></ul><ul><ul><li>Fuel flow specifications are usually expressed in gallons per minute </li></ul></ul><ul><ul><li>Typical specification would be 0.5 gallons per minute or more </li></ul></ul>
  119. 119. Figure 77-26 A fuel-pressure reading does not confirm that there is enough fuel volume for the engine to operate correctly.
  120. 120. Figure 77-27 A fuel system tester connected in series in the fuel system so all of the fuel used flows through the meter which displays the rate-of-flow and the fuel pressure.
  121. 121. Fuel Pump Testing <ul><li>Testing Fuel-Pump Volume </li></ul><ul><ul><li>Fuel must be filtered to prevent contaminants from damaging fuel system components or engine </li></ul></ul><ul><ul><li>Fuel filters accumulate these contaminants </li></ul></ul>
  122. 122. Fuel Pump Testing <ul><li>Testing Fuel-Pump Volume </li></ul><ul><ul><li>Clogged filter can reduce fuel-pump volume </li></ul></ul><ul><ul><li>Clogged filter can result in the following: </li></ul></ul><ul><ul><ul><li>Low power at higher engine speeds. </li></ul></ul></ul><ul><ul><ul><ul><li>Vehicle may not go faster than a certain speed </li></ul></ul></ul></ul>
  123. 123. Fuel Pump Testing <ul><li>Testing Fuel-Pump Volume </li></ul><ul><ul><li>Clogged filter can result in the following: </li></ul></ul><ul><ul><ul><li>Engine will cut out or miss on acceleration. </li></ul></ul></ul>
  124. 124. Fuel Pump Testing <ul><li>Testing Fuel-Pump Volume </li></ul><ul><ul><li>Clogged filter can result in the following: </li></ul></ul><ul><ul><ul><li>Weak fuel pump can also cause additional problems: </li></ul></ul></ul><ul><ul><ul><ul><li>Engine may be hard to start. </li></ul></ul></ul></ul>
  125. 125. Fuel Pump Testing <ul><li>Testing Fuel-Pump Volume </li></ul><ul><ul><li>Clogged filter can result in the following: </li></ul></ul><ul><ul><ul><li>Weak fuel pump can also cause additional problems: </li></ul></ul></ul><ul><ul><ul><ul><li>Rough idling and stalling. </li></ul></ul></ul></ul>
  126. 126. Fuel Pump Testing <ul><li>Testing Fuel-Pump Volume </li></ul><ul><ul><li>Clogged filter can result in the following: </li></ul></ul><ul><ul><ul><li>Weak fuel pump can also cause additional problems: </li></ul></ul></ul><ul><ul><ul><ul><li>Erratic shifting of automatic transmission. </li></ul></ul></ul></ul>
  127. 127. Fuel Pump Testing <ul><li>Testing Fuel-Pump Volume </li></ul><ul><ul><li>CAUTION: Be certain to consult vehicle manufacturer’s recommended service and testing procedures before attempting to test or replace any component of a high-pressure electronic fuel-injection system. </li></ul></ul>
  129. 129. Fuel-Pump Current Draw Test <ul><li>Another useful test for fuel pump is to measure current draw in amperes </li></ul><ul><li>Connect digital multimeter set to read DC amperes </li></ul><ul><li>Test current draw </li></ul>
  130. 130. Fuel-Pump Current Draw Test <ul><li>Compare reading to factory specifications </li></ul><ul><ul><li>NOTE: Testing the current draw of an electric fuel pump may not indicate whether the pump is good. A pump that is not rotating may draw normal current. </li></ul></ul>
  131. 131. Figure 77-29 Hookup for testing fuel-pump current draw on any vehicle equipped with a fuel-pump relay.
  132. 132. Fuel-Pump Current Draw Test <ul><li>Using mini clamp-on ammeter is easy way to measure fuel pump current </li></ul><ul><li>Clamp the inductive probe around a wire to fuel pump </li></ul><ul><li>Add a fused jumper wire to replace fuel pump fuse </li></ul><ul><li>Start engine and read the meter display </li></ul>
  134. 134. Fuel-Pump Replacement <ul><li>Follow these recommendations whenever replacing electric fuel pump: </li></ul><ul><ul><li>Clean around fuel pump retainer area before removing the fuel pump assembly </li></ul></ul><ul><ul><li>Fuel-pump strainer (sock) should be replaced with the new pump </li></ul></ul>
  135. 135. Fuel-Pump Replacement <ul><li>Follow these recommendations whenever replacing electric fuel pump: </li></ul><ul><ul><li>If original pump had defector shield, use it to prevent fuel return bubbles from blocking the inlet to pump </li></ul></ul><ul><ul><li>Always check the fuel tank for evidence of contamination </li></ul></ul>
  136. 136. Fuel-Pump Replacement <ul><li>Follow these recommendations whenever replacing electric fuel pump: </li></ul><ul><ul><li>Double-check that replacement pump is correct for the application </li></ul></ul><ul><ul><li>Check that the wiring and electrical connectors are clean and tight </li></ul></ul>
  138. 138. Fuel Supply-Related Symptom Guide <ul><li>Pressure too high after engine start-up. </li></ul><ul><ul><li>Defective fuel-pressure regulator </li></ul></ul><ul><ul><li>Restricted fuel return line </li></ul></ul><ul><ul><li>Excessive system voltage </li></ul></ul><ul><ul><li>Wrong fuel pump </li></ul></ul>
  139. 139. Fuel Supply-Related Symptom Guide <ul><li>Pressure too low after engine start-up. </li></ul><ul><ul><li>Stuck-open pressure regulator </li></ul></ul><ul><ul><li>Low voltage </li></ul></ul><ul><ul><li>Poor ground </li></ul></ul><ul><ul><li>Plugged fuel filter </li></ul></ul>
  140. 140. Fuel Supply-Related Symptom Guide <ul><li>Pressure too low after engine start-up. </li></ul><ul><ul><li>Faulty inline fuel pump </li></ul></ul><ul><ul><li>Faulty in-tank fuel pump </li></ul></ul><ul><ul><li>Partially clogged filter sock </li></ul></ul><ul><ul><li>Faulty hose coupling </li></ul></ul>
  141. 141. Fuel Supply-Related Symptom Guide <ul><li>Pressure too low after engine start-up. </li></ul><ul><ul><li>Leaking fuel line </li></ul></ul><ul><ul><li>Wrong fuel pump </li></ul></ul><ul><ul><li>Leaking pulsator </li></ul></ul><ul><ul><li>Restricted accumulator </li></ul></ul>
  142. 142. Fuel Supply-Related Symptom Guide <ul><li>Pressure too low after engine start-up. </li></ul><ul><ul><li>Faulty pump check valves </li></ul></ul><ul><ul><li>Faulty pump installation </li></ul></ul>
  143. 143. Fuel Supply-Related Symptom Guide <ul><li>Pressure drops off with key on/engine off. With key off, the pressure does not hold. </li></ul><ul><ul><li>Leaky pulsator </li></ul></ul><ul><ul><li>Leaking fuel-pump coupling hose </li></ul></ul><ul><ul><li>Faulty fuel pump (check valves) </li></ul></ul><ul><ul><li>Faulty pressure regulator </li></ul></ul>
  144. 144. Fuel Supply-Related Symptom Guide <ul><li>Pressure drops off with key on/engine off. With key off, the pressure does not hold. </li></ul><ul><ul><li>Leaking fuel injector </li></ul></ul><ul><ul><li>Faulty installation </li></ul></ul><ul><ul><li>Lines leaking </li></ul></ul>
  145. 145. (TECH TIP page 872)
  146. 146. FREQUENTLY ASKED QUESTION <ul><li>Just How Much Fuel Is Recirculated? </li></ul><ul><ul><li>Approximately 80% of the available fuel-pump volume is released to the fuel tank through the fuel pressure regulator at idle speed. As an example, a passenger vehicle cruising down the road at 60 mph gets 30 mpg. </li></ul></ul>? BACK TO PRESENTATION <ul><li>With a typical return-style fuel system pumping about 30 gallons per hour from the tank, it would therefore burn 2 gallons per hour, and return about 28 gallons per hour to the tank! </li></ul>
  147. 147. FREQUENTLY ASKED QUESTION <ul><li>How Can an Electric Pump Work Inside a Gas Tank and Not Cause a Fire? </li></ul><ul><ul><li>Even though fuel fills the entire pump, no burnable mixture exists inside the pump because there is no air and no danger of commutator brush arcing, igniting the fuel. </li></ul></ul>? BACK TO PRESENTATION
  148. 148. FREQUENTLY ASKED QUESTION <ul><li>Why Are Many Fuel-Pump Modules Spring-Loaded? </li></ul><ul><ul><li>Fuel modules that contain the fuel pickup sock, fuel pump, and fuel level sensor are often spring-loaded when fitted to a plastic fuel tank. </li></ul></ul>? BACK TO PRESENTATION <ul><li>The plastic material shrinks when cold and expands when hot, so having the fuel module spring-loaded ensures that the fuel pickup sock will always be the same distance from the bottom of the tank. </li></ul><ul><ul><li>Figure 77-16 A typical fuel-pump module assembly, which includes the pickup strainer and fuel pump, as well as the fuelpressure sensor and fuel level sensing unit. </li></ul></ul>
  149. 149. TECH TIP <ul><li>Be Sure That the Fuel Filter Is Installed Correctly </li></ul><ul><ul><li>The fuel filter has flow direction and if it is installed backwards, the vehicle will most likely have a restricted exhaust (low power at higher engine speeds and loads). </li></ul></ul>BACK TO PRESENTATION <ul><li>All injectors, throttle body or port, are fitted with one or more filter screens or strainers to remove any particles (generally 10 microns or 0.00039 in.) that might have passed through the other filters. These screens, which surround the fuel inlet, are on the side of throttle-body injectors and are inserted in the top of port injectors. </li></ul><ul><ul><li>Figure 77-20 The final filter, also called a filter basket , is the last filter in the fuel system. </li></ul></ul>
  150. 150. TECH TIP <ul><li>The Ear Test </li></ul><ul><ul><li>No, this is not a test of your hearing, but rather using your ear to check that the electric fuel pump is operating. The electric fuel pump inside the fuel tank is often difficult to hear running, especially in a noisy shop environment. A commonly used trick to better hear the pump is to use a funnel in the fuel filter neck. </li></ul></ul>BACK TO PRESENTATION <ul><ul><li>Figure 77-21 (a) A funnel helps in hearing if the electric fuel pump inside the gas tank is working. </li></ul></ul><ul><ul><li>Figure 77-21 (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. </li></ul></ul>
  151. 151. TECH TIP <ul><li>The Rubber Mallet Trick </li></ul><ul><ul><li>Often a no-start condition is due to an inoperative electric fuel pump. A common trick is to tap on the bottom of the fuel tank with a rubber mallet in an attempt to jar the pump motor enough to work. </li></ul></ul><ul><li>Instead of pushing a vehicle into the shop, simply tap on the fuel tank and attempt to start the engine. This is not a repair, but rather a confirmation that the fuel pump does indeed require replacement. </li></ul>BACK TO PRESENTATION
  152. 152. TECH TIP <ul><li>The Fuel-Pressure Stethoscope Test </li></ul><ul><ul><li>When the fuel pump is energized and the engine is not running, fuel should be heard flowing back to the fuel tank at the outlet of the fuel-pressure regulator. </li></ul></ul>BACK TO PRESENTATION <ul><li>If fuel is heard flowing through the return line, the fuel-pump pressure is higher than the regulator pressure. If no sound of fuel is heard, either the fuel pump or the fuel-pressure regulator is at fault. </li></ul><ul><ul><li>Figure 77-25 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. </li></ul></ul>
  153. 153. TECH TIP <ul><li>Quick and Easy Fuel Volume Test </li></ul><ul><ul><li>Testing for pump volume involves using a specialized tester or a fuel-pressure gauge equipped with a hose to allow the fuel to be drawn from the system into a container with volume markings to allow for a volume measurement. This test can be hazardous because of flammable gasoline vapors. </li></ul></ul>BACK TO PRESENTATION <ul><li>An alternative test involves connecting a fuel-pressure gauge to the system with the following steps: </li></ul><ul><li>STEP 1 Start the engine and observe the fuel-pressure gauge. The reading should be within factory specifications (typically between 35 PSI and 45 PSI). </li></ul><ul><li>STEP 2 Remove the hose from the fuel-pressure regulator. The pressure should increase if the system uses a demand-type regulator. </li></ul><ul><li>STEP 3 Rapidly accelerate the engine while watching the fuel-pressure gauge. If the fuel volume is okay, the fuel pressure should not drop more than 2 PSI. If the fuel pressure drops more than 2 PSI, replace the fuel filter and retest. </li></ul><ul><li>STEP 4 After replacing the fuel filter, accelerate the engine and observe the pressure gauge. If the pressure drops more than 2 PSI, replace the fuel pump. </li></ul><ul><li>NOTE: The fuel pump could still be delivering less than the specified volume of fuel, but as long as the volume needed by the engine is met, the pressure will not drop. If, however, the vehicle is pulling a heavy load, the demand for fuel volume may exceed the capacity of the pump. </li></ul>
  154. 154. TECH TIP <ul><li>Remove the Bed to Save Time? </li></ul><ul><ul><li>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. </li></ul></ul>BACK TO PRESENTATION <ul><li>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. </li></ul><ul><li>CAUTION: Be sure to clean around the fuel pump opening so that dirt or debris does not enter the tank when the fuel pump is removed. </li></ul><ul><ul><li>Figure 77-28 A fuel system tester connected in series in the fuel system so all of the fuel used flows through the meter which displays the rate-of-flow and the fuel pressure. </li></ul></ul>