at 43 ch 24 fuel injection system diagnosis

Automotive Fuel and Emissions Control Systems, 2/eBy James D. Halderman and Jim Linder

© 2009 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

PORT FUEL-INJECTION PRESSURE REGULATOR DIAGNOSIS

FIGURE 24-1 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.



PRESSURE TRANSDUCER FUEL PRESSURE TEST

FIGURE 24-2 (a) A fuel-pressure graph after key on, engine off (KOEO). (b) Pressure drop after 10 minutes on a normal port fuel-injection system.



DIAGNOSING ELECTRONIC FUEL-INJECTION PROBLEMS USING VISUAL INSPECTION• All fuel-injection systems require the proper amount of clean

fuel delivered to the system at the proper pressure and the correct amount of filtered air.

• The following items should be carefully inspected before proceeding to more detailed tests.– Check the air filter and replace as needed.– Check the air induction system for obstructions.– Check the conditions of all vacuum hoses. Replace any hose that is

split, soft (mushy), or brittle.– Check the positive crankcase ventilation (PCV) valve for proper

operation or replacement as needed– Check all fuel-injection electrical connections for corrosion or

damage.– Check for gasoline at the vacuum port of the fuel-pressure regulator if

the vehicle is so equipped.



DIAGNOSING ELECTRONIC FUEL-INJECTION PROBLEMS USING VISUAL INSPECTION

FIGURE 24-3 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.



STETHOSCOPE FUELINJECTION TEST

FIGURE 24-4 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.



SCAN TOOL VACUUM LEAK DIAGNOSIS

• If a vacuum (air) leak occurs on an engine equipped with a speed-density-type of fuel injection, the extra air would cause the following to occur:– The idle speed increases due to the extra air just as if the

throttle pedal was depressed.– The MAP sensor reacts to the increased air from the

vacuum leak as an additional load on the engine.– The computer increases the injector pulse width slightly

longer due to the signal from the MAP sensor.– The air-fuel mixture remains unchanged.– The idle air control (IAC) counts will decrease, thereby

attempting to reduce the engine speed to the target idle speed stored in the computer memory.



SCAN TOOL VACUUM LEAK DIAGNOSIS

FIGURE 24-6 Using a scan tool to check for IAC counts or percentage as part of a diagnostic routine.



PORT FUEL-INJECTION SYSTEM DIAGNOSIS

• To determine if a port fuel-injection system—including the fuel pump, injectors, and fuel-pressure regulator—are operating correctly, take the following steps.– Attach a fuel-pressure gauge to the Schrader valve on the fuel rail.– Turn the ignition key on or start the engine to build up the fuel-pump

pressure (to about 35 to 45 PSI).– Wait 20 minutes and observe the fuel pressure retained in the fuel

rail and note the PSI reading. • The check valve in the fuel pump• Leaking injectors, lines, or fittings• A defective (leaking) fuel-pressure regulator• Reenergize the electric fuel pump.• Clamp the fuel supply line, and wait 10 minutes (see caution box). If the pressure

drop does not occur, replace the fuel pump. If the pressure drop still occurs, continue with the next step.




FIGURE 24-7 Checking the fuel pressure using a fuel-pressure gauge connected to the Schrader valve.




• To determine which unit is defective, perform the following:– Reenergize the electric fuel pump.– Clamp the fuel supply line, and wait 10 minutes (see

caution box). If the pressure drop does not occur, replace the fuel pump. If the pressure drop still occurs, continue with the next step.

– Repeat the pressure buildup of the electric pump and clamp the fuel return line.

– If the pressure drop still occurs, one or more of the injectors is leaking. Remove the injectors with the fuel rail and hold over paper. Replace those injectors that drip one or more drops after 10 minutes with pressurized fuel.




FIGURE 24-8 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

• One of the first checks that should be performed when diagnosing a no-start condition is whether the fuel injectors are being pulsed by the computer.

• Checking for proper pulsing of the injector is also important in diagnosing a weak or dead cylinder.




FIGURE 24-9 (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.




• Possible noid light problems and causes include the following:– The light is off and does

not flash. – The noid light flashes

dimly. – The noid light is on and

does not flash.

FIGURE 24-10 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

• Each port fuel injector must deliver an equal amount of fuel or the engine will idle roughly or perform poorly.

• The electrical balance test involves measuring the injector coil-winding resistance.

• For best engine operation, all injectors should have the same electrical resistance.

• To measure the resistance, carefully release the locking feature of the connector and remove the connector from the injector.



CHECKING FUEL-INJECTOR RESISTANCE

FIGURE 24-11 Connections and settings necessary to measure fuel-injector resistance. (Courtesy of Fluke Corporation)



MEASURING RESISTANCE OF GROUPED INJECTORS• To measure the resistance of these injectors, it is

often easiest to measure each group of three that is wired in parallel.

• The resistance of three injectors wired in parallel is one-third of the resistance of each individual injector.

• For example,– Injector resistance = 12 ohms (Ω)– Three injectors in parallel = 4 ohms (Ω)



MEASURING RESISTANCE OF INDIVIDUAL INJECTORS• While there are many ways

to check injectors, the first test is to measure the resistance of the coil inside and compare it to factory specifications.

FIGURE 24-14 If an injector has the specified resistance, that does not mean that it is okay. This injector had the specified resistance yet did not deliver the specified amount of fuel because it was clogged.



PRESSURE-DROP BALANCE TEST

• The pressure balance test involves using an electrical timing device to pulse the fuel injectors on for a given amount of time, usually 500 ms or 0.5 second, and observing the drop in pressure that accompanies the pulse.

• If the fuel flow through each injector is equal, the drop in pressure in the system will be equal.



PRESSURE-DROP BALANCE TEST

FIGURE 24-15 Connect a fuel-pressure gauge to the fuel rail at the Schrader valve.



SCOPE TESTING FUEL INJECTORS

• A scope (analog or digital storage) can be connected into each injector circuit.

• There are three types of injector-driven drive circuits and each type of circuit has its own characteristic pattern.

FIGURE 24-17 A digital storage oscilloscope can be easily connected to an

injector by carefully back probing the electrical connector.



SCOPE TESTING FUEL INJECTORS

• Saturated Switch Type• Peak-and-Hold Type• Pulse-Width Modulated

Type

FIGURE 24-18 The injector on-time is called the pulse width. (Courtesy of Fluke

Corporation)



IF THREE OF SIX INJECTORS ARE DEFECTIVE, SHOULD I ALSO REPLACE THE OTHER THREE?

FIGURE 24-20 A set of six reconditioned injectors.



IDLE AIR SPEED CONTROL DIAGNOSIS

• On an engine equipped with fuel injection (TBI or port injection), the idle speed is controlled by increasing or decreasing the amount of air bypassing the throttle plate.

• 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).




FIGURE 24-21 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.




FIGURE 24-22 A typical IAC. FIGURE 24-23 Some IAC units are purchased with the housing as shown. Carbon buildup in these passages can cause a rough or unstable idling or stalling.



THERE IS NO SUBSTITUTE FOR A THOROUGH VISUAL INSPECTION

FIGURE 24-24 (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.



FUEL-INJECTION SERVICE

FIGURE 24-26 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.



FUEL-PUMP RELAY CIRCUIT DIAGNOSIS

at 43 ch 24 fuel injection system diagnosis

Documents

automotive fuel

fuel injectors

fuelpump pressure

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