Chapter 60

[object Object],[object Object],[object Object],OBJECTIVES: After studying Chapter 60, the reader should be able to: Continued

[object Object],[object Object],[object Object],OBJECTIVES: After studying Chapter 60, the reader should be able to:

[object Object],PORT FUEL-INJECTION PRESSURE REGULATOR DIAGNOSIS Continued

[object Object],Continued NOTE: If gasoline drips out of the vacuum hose when removed from the fuel-pressure regulator, the regulator is defective and will require replacement. ,[object Object],[object Object],[object Object]

Figure 60–1 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. Continued ,[object Object],NOTE: Some vehicles do not use a vacuum-regulated fuel-pressure regulator. Many of these vehicles use a regulator located inside the fuel tank that supplies a constant fuel pressure to the fuel injectors.

[object Object],Pressure Transducer Fuel Pressure Test (a) (b) Figure 60–2 (a) A fuel-pressure graph after key on, engine off (KOEO). (b) Pressure drop after 10 minutes on a normal port fuel-injection system.

[object Object],DIAGNOSING ELECTRONIC FUEL-INJECTION PROBLEMS USING VISUAL INSPECTION Continued ,[object Object],[object Object],[object Object],[object Object],The following items should be carefully inspected before proceeding to more detailed tests.

Figure 60–3 A clogged PCV system caused the engine oil fumes to be drawn into the air cleaner assembly. This is what the technician discovered during a visual inspection. NOTE: Use of an incorrect PCV valve can cause a rough idle or stalling. ,[object Object],[object Object]

[object Object],Stethoscope Fuel Injection Test - Part 1 Figure 60–4 All fuel injectors should make the same sound with the engine running at idle speed. A lack of sound indicates a possible electrically open injector or a break in the wiring. A defective computer could also be the cause of a lack of clicking (pulsing) of the injectors.

[object Object],Stethoscope Fuel Injection Test - Part 2 Figure 60–5 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.

[object Object],Quick and Easy Leaking Injector Test

SCAN TOOL VACUUM LEAK DIAGNOSIS ,[object Object],Continued ,[object Object],[object Object],[object Object],[object Object],[object Object]

Figure 60–6 Using a scan tool to check for IAC counts or percentage as part of a diagnostic routine. Continued

[object Object],Continued ,[object Object],[object Object],[object Object]

[object Object],No Spark, No Squirt

PORT FUEL INJECTION SYSTEM DIAGNOSIS ,[object Object],[object Object],Figure 60–7 Checking the fuel pressure using a fuel pressure gauge connected to the Schrader valve. Continued ,[object Object]

[object Object],Continued ,[object Object],[object Object],[object Object],To determine which unit is defective, perform the following: ,[object Object],[object Object],If the drop is less than 20 psi in 20 minutes, everything is okay; if the drop is greater, there is a possible problem with:

[object Object],[object Object],CAUTION: Do not clamp plastic fuel lines. Connect shutoff valves to the fuel system to shut off supply and return lines. Figure 60–8 Shutoff valves must be used on vehicles equipped with plastic fuel lines to isolate the cause of a pressure drop in the fuel system.

TESTING FOR AN INJECTOR PULSE ,[object Object],Continued NOTE: The term noid is simply an abbreviation of the word sole noid . Injectors use a movable iron core and are therefore solenoids. Therefore, a noid light is a replacement for the solenoid (injector).

[object Object],Figure 60–9 (a) Noid lights are usually purchased as an assortment so that one is available for any type or size of injector wiring connector. (b) The connector is unplugged from the injector and a noid light is plugged into the injector connector. The noid light should flash when the engine is being cranked if the power circuit and the pulsing to ground by the computer are functioning okay. Continued (a) (b)

CAUTION: A noid lamp must be used with caution. The computer may show a good noid light operation and have low supply voltage. Figure 60–10 Use a DMM set to read DC volts to check the voltage drop of the positive circuit to the fuel injector. A reading of 0.5 volt or less is generally considered to be acceptable.

CHECKING FUEL INJECTOR RESISTANCE ,[object Object],Continued With an ohmmeter, measure the resistance across the injector terminals. Be sure to use the low-ohms feature of the digital ohmmeter to read in tenths (0.1) of an ohm. NOTE: Some engines require specific procedures to gain access to the injectors. Always follow the manufacturers’ recommended procedures. See Figures 60–11 and 60–12. To measure the resistance, carefully release the locking feature of the connector and remove the connector from the injector.

[object Object],Continued See the chart on Page 723 of your textbook. The resistance should be measured twice—once when the engine (and injectors) are cold and after the engine has reached normal operating temperature.

[object Object],Figure 60–12 To measure fuel-injector resistance, a technician constructed a short wiring harness with a double banana plug that fits into the V and COM terminals of the meter and an injector connector at the other end. This setup makes checking resistance of fuel injectors quick and easy. Figure 60–11 Connections and settings necessary to measure fuel-injector resistance.

[object Object],MEASURING RESISTANCE OF GROUPED INJECTORS Continued Injector resistance = 12 ohms (Ω) Three injectors in parallel = 4 ohms (Ω)

Figure 60–13 (a) The meter is connected to read one group of three 12-ohm injectors. The result should be 4 ohms and this reading is low, indicating at least one injector is shorted (low resistance). (b) This meter is connected to the other group of 3 injectors and indicates most injectors are shorted. The technician replaced all six injectors and the engine ran great. ,[object Object]

[object Object],MEASURING RESISTANCE OF INDIVIDUAL INJECTORS Continued Figure 60–14 Measuring injector resistance using a DMM and an injector connector. This setup was made by the technician and makes measuring injector resistance fast and easy. Unplug the connector and measure resistance of each injector at the injector side of the connector.

[object Object],Equal Resistance test

PRESSURE DROP BALANCE TEST ,[object Object],Continued

[object Object],Continued ,[object Object],[object Object],[object Object],[object Object]

[object Object],Figure 60–15 Connect a fuel pressure gauge to the fuel rail on the Schrader valve. Step #1 Attach the pressure gauge to the fuel delivery rail on the supply side. Make sure the connections are safe and leak proof. Step #4 Activate the pulser for the timed firing pulses. Step #5 Note and record the new static rail pressure after the injector has been pulsed. Step #2 Attach the injector pulser to the first injector to be tested. Step #3 Turn the ignition key to the on position to prime the fuel rail. Note the static fuel pressure reading. Continued

[object Object],See the chart on Page 725 of your textbook.

INJECTOR VOLTAGE DROP TESTS ,[object Object],Figure 60–16 An injector tester being used to check the voltage drop through the injector while the tester is sending current through the injectors. This test is used to check the coil inside the injector. This same tester can be used to check for equal pressure drop of each injector by pulsing the injector on for 500 ms. Continued The tester, which is recommended for use by GM, pulses the injector while a digital multimeter is connected to the unit.

[object Object],CAUTION: Do not test an injector using a pulse-type tester more than one time without starting the engine to help avoid a hydrostatic lock caused by the flow of fuel into the cylinder during the pulse test.

SCOPE TESTING FUEL INJECTORS ,[object Object],Continued Here for an example of how to connect a scope to read a fuel-injector waveform. Figure 60–17 A digital storage oscilloscope can be easily connected to an injector by carefully back probing the electrical connector.

Figure 60–18 The injector on-time is called the pulse width. Continued

Figure 60–19 A typical peak-and-hold fuel-injector waveform. Most fuel injectors that measure less than 6 ohms will usually display a similar waveform. Continued

[object Object],[object Object],If Three of Six Injectors Are Defective, Should I Also Replace the Other Three? ,[object Object],[object Object],[object Object]

IDLE AIR SPEED CONTROL DIAGNOSIS ,[object Object],Again, an electronic stepper motor or pulse-width modulated solenoid is used to maintain the correct idle speed This control is often called the idle air control ( IAC ). See Figures 60–22 and 60–23. Figure 60–21 An IAC controls idle speed by controlling the amount of air that passes around the throttle plate. More airflow results in a higher idle speed.

[object Object],Figure 60–23 Some IAC units are purchased with the housing as shown. Carbon buildup in these passages can cause a rough or unstable idling or stalling. Continued Figure 60–22 A typical IAC.

[object Object],There is No Substitute for a Thorough Visual Inspection Figure 60–24 (a) Nothing looks unusual when the hood is first opened. (b) When the cover is removed from the top of the engine, a mouse or some other animal nest is visible. The animal had already eaten through a couple of injector wires. At least the cause of the intermittent misfire was discovered. (a) (b)

FUEL INJECTION SERVICE ,[object Object],Continued

[object Object],Figure 60–25 Checking fuel-pump volume using a hose from the outlet of the fuel pressure regulator into a calibrated container. 1. Check fuel - pump operating pressure and volume Most working technicians assume that if the pressure is correct, the volume is also OK. Use a fuel-pressure tester to the fuel rail inlet to quickly test the fuel pressure with the engine running. At the same time, test the volume of the pump by sending fuel into the holding tank. (One ounce per second is the usual specification.) Continued

Figure 60–26 Testing fuel-pump volume using a fuel-pressure gauge with a bleed hose inserted into a suitable container. The engine is running during this test.

Figure 60–27 A typical two-line cleaning machine hookup, showing an extension hose that can be used to squirt a cleaning solution into the throttle body while the engine is running on the cleaning solution and gasoline mixture.

[object Object],[object Object],[object Object],Continued More items to consider:

[object Object],Continued Check the Injectors at the “Bends and Ends” Injectors that are most likely to become restricted due to clogging of the filter basket screen are the injectors at the ends of the rail especially on returnless systems where dirt can accumulate. Also the injectors that are located at the bends of the fuel rail are also subject to possible clogging due to the dirt being deposited where the fuel makes a turn in the rail.

[object Object],Figure 60–28 To thoroughly clean a throttle body, it is sometimes best to remove it from the vehicle. Clean the areas as needed, then use a handheld fuel injector connected in parallel with the pressure hose, along with a pulser to allow cleaning of the throttle plates with the same chemical as injectors are running on. This works well as air is drawn into IAC passages on a running engine and will clean the passages without IAC removal.

[object Object],This service usually takes approximately one hour for the vehicle to run out of fuel and the entire service to be performed. The good thing is that the technician may do other services while this is being performed. Some technicians may install a set of plugs or change the fuel filter while the engine is flushing. This service should restore the fuel system to original operations. Continued

[object Object],Be Sure To Clean the Fuel Rail

See the chart on Page 729 of your textbook.

FUEL SYSTEM SCAN TOOL DIAGNOSTICS ,[object Object],[object Object],[object Object],Continued

See the chart on Page 730 of your textbook.

[object Object],( cont. ) Continued

SUMMARY ,[object Object],[object Object],[object Object],[object Object],Continued

SUMMARY ,[object Object],[object Object],[object Object],( cont. )

Chapter 60

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Chapter 60