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Figure 19.1If 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.
Figure 19.2aA fuel-pressure graph after key on, engine off (KOEO).
Figure 19.2bPressure drop after 10 minutes on a normal port fuel-injection system.
Figure 19.3A 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.
Figure 19.4 All fuel injectors should make the same sound with the engine running at idle speed. A lack of sound could indicate an electrically open injector, a break in the wiring, or a stuck closed injector. A defective computer could also be the cause of a lack of clicking (pulsing) of the injectors.
Figure 19.5Fuel should be heard returning to the fuel tank at the fuel return line if the fuel-pump and fuel-pressure regulator are functioning correctly.
Figure 19.6A scan tool can be used to help diagnose vacuum leaks by looking at the commanded IAC counts.
Figure 19.7A fuel-pressure gauge connected to the fuel-pressure tap (Schrader valve) on a port fuel-injected V-6 engine.
Figure 19.8Shutoff valves must be used on vehicles equipped with plastic fuel lines to isolate the cause of a pressure drop in the fuel system.
Figure 19.9aNoid lights are usually purchased as an assortment so that one is available for any type or size of injector wiring connector.
Figure 19.9bThe 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.
Figure 19.10Use 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.
Figure 19.11Connections and settings necessary to measure fuel-injector resistance. (Courtesy of Fluke Corporation)
Figure 19.12To 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 19.13The fuel-injector wiring connector on an older General Motors 3.1-liter V-6 is hidden and attached to the rear of the intake manifold. Both groups of three injectors can be easily measured using an ohmmeter.Both groups of injectors should measure within 0.5 ohm of each other. Newer engines have a connector that is harder to reach. Check service information for details.
Figure 19.14Note the fuel pressure before and after pulsing the injector on for 500 ms to help determine if the injector is flowing the same amount of fuel as all of the other injectors.
Figure 19.15This General Motors specified tester is used to measure not only the pressure drop caused by pulsing an injector on for 500 ms, but can also be used to measure the voltage drop across the windings.
Figure 19.16A digital storage oscilloscope can be easily connected to an injector by carefully back probing the electrical connector. (Courtesy of Fluke Corporation)
Figure 19.17A typical injector voltage waveform. Notice that the battery voltage is reduced to zero when the injector is grounded by the computer. The injector on-time is then represented by the line near zero voltage.When the computer turns off the injector, a voltage spike is generated by the collapsing magnetic field created by the injector windings.
Figure 19.18The injector on-time is called the pulse width. (Courtesy of Fluke Corporation)
Figure 19.19A peak-and-hold type of fuel injector such as this TBI can be easily connected to a digital storage oscilloscope by carefully back probing the electrical connector. (Courtesy of Fluke Corporation)
Figure 19.20A typical peak-and-hold fuel-injector waveform. Most fuel injectors that measure less than 6 ohms will usually display a similar waveform. (Courtesy of Fluke Corporation)
Figure 19.21A peak-and-hold injector waveform. (Courtesy of Fluke Corporation)
Figure 19.22A typical waveform for a pulse-width modulated fuel injector. (Courtesy of Fluke Corporation)
Figure 19.23A typical waveform created by current ranging the operation of a fuel injector. The slight dip in the waveform, sometimes called the “gull wing,” about two-thirds of the way up the “ramp” indicates when the pintle of the fuel injector actually opens. If it opens higher, a dirty pintle is indicated; if it opens lower, a worn injector pintle or a broken pintle return spring is indicated.
Figure 19.24A comparison of a current waveform (top) and a voltage waveform (bottom) of a peak-and-hold TBI injector.
Figure 19.26An IAC controls idle speed by controlling the amount of air that passes around the throttle plate. More airflow results in a higher idle speed. (Courtesy of Fluke Corporation)
Figure 19.28Some IAC units are purchased with the housing as shown. Carbon buildup in these passages can cause a rough or unstable idling or stalling.
Figure 19.29aNothing looks unusual when the hood is first opened.
Figure 19.29bWhen 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.
Figure 19.30aDirty throttle plate. This throttle plate was so dirty that the technician removed the entire throttle body to be sure it was thoroughly cleaned.
Figure 19.30bMost throttle plates can be cleaned on the vehicle using a brush and throttle body cleaner. Be sure the cleaner is safe for oxygen sensors.
Figure 19.31Some vehicles, such as this Ford, have labels on the throttle body to warn against cleaning of the throttle plates. A slippery coating is placed on the throttle plate and throttle bore that prevents deposits from sticking. Cleaning this type of housing can remove this protective coating.
Figure 19.32aChecking fuel pump value using a hose from the outlet of the fuel-pressure regulator into a calibrated container.
Figure 19.32bTesting fuel-pump volume using a fuel-pressure gauge with a bleed hose into a suitable container. The engine is running during this test.
Figure 19.33A 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.
Figure 19.34aA close up of an auxiliary nozzle from a fuel-injector cleaning machine used to clean the air intake.
Figure 19.34bThe metal line is inserted into the throttle body and the engine is run with a combination of cleaner and gasoline flowing through the nozzle.
Figure 19.35bOften an injector problem is a fuel rail problem instead.
Figure 19.36This TBI pressure regulator spring came out in pieces when the regulator cover was removed.
