<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><li>Describe how to check an electric fuel pump for proper pressure and volume delivery. </li></ul><ul><li>Explain how to check a fuel-pressure regulator. </li></ul>OBJECTIVES: After studying Chapter 60, the reader should be able to: Continued
<ul><li>Describe how to test fuel injectors. </li></ul><ul><li>Explain how to diagnose electronic fuel injection problems. </li></ul><ul><li>Describe how to service the fuel injection system. </li></ul>OBJECTIVES: After studying Chapter 60, the reader should be able to:
<ul><li>Most port-fuel-injected engines use a vacuum hose connected to the fuel-pressure regulator. At idle, the pressure inside the intake manifold is low (high vacuum). Manifold vacuum is applied above the diaphragm inside the fuel-pressure regulator. This reduces the pressure exerted on the diaphragm and results in a lower, about 10 psi (69 kPa), fuel pressure applied to the injectors. </li></ul>PORT FUEL-INJECTION PRESSURE REGULATOR DIAGNOSIS Continued
<ul><li>To test a vacuum-controlled fuel-pressure regulator: </li></ul>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. <ul><li>Connect a fuel-pressure gauge to monitor the fuel pressure. </li></ul><ul><li>Locate the fuel-pressure regulator and disconnect the vacuum hose from the regulator. </li></ul><ul><li>With the engine running at idle speed, reconnect the vacuum hose to the fuel-pressure regulator while watching the fuel-pressure gauge. The fuel pressure should drop (about 10 psi or 69 kPa) when the hose is reattached to the regulator. </li></ul>
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 <ul><li>Using a hand-operated vacuum pump, apply vacuum (20 in. Hg) to the regulator. The regulator should hold vacuum. If the vacuum drops, replace the fuel-pressure regulator. </li></ul>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.
<ul><li>Using a pressure transducer and a graphing multimeter (GMM) or digital storage oscilloscope (DSO) allows the service tech to view fuel pressure over time, Figure a. Note the fuel pressure dropped from 15 to 6 psi on a TBI-equipped vehicle after one minute. Normal pressure holding capability is shown in Figure b, when pressure dropped about 10% after 10 minutes. </li></ul>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.
<ul><li>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. </li></ul>DIAGNOSING ELECTRONIC FUEL-INJECTION PROBLEMS USING VISUAL INSPECTION Continued <ul><li>Check the air filter and replace as needed. </li></ul><ul><li>Check the air induction system for obstructions. </li></ul><ul><li>Check the conditions of all vacuum hoses. Replace any hose that is split, soft (mushy), or brittle. </li></ul><ul><li>Check all fuel-injection electrical connections for corrosion or damage. </li></ul>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. <ul><li>Check the positive crank- case ventilation (PCV) valve for proper operation or replacement as needed. </li></ul><ul><li>Check for gasoline at the vacuum port of the fuel-pressure regulator if the vehicle is so equipped. Gasoline in the vacuum hose at the fuel-pressure regulator indicates that the regulator is defective and requires replacement. </li></ul>
<ul><li>A common test for injector operation is to listen to the injector using a stethoscope with the engine at idle speed. All injectors should produce the same clicking sound. If an injector makes a clunking or rattling sound, it should be tested further or replaced. </li></ul>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.
<ul><li>With the engine still running, place the end of the stethoscope probe to the return line from the fuel-pressure regulator. Fuel should be heard flowing back to the fuel tank if the fuel-pump pressure is higher than the fuel-regulator pressure. If no sound of fuel is heard, then either the fuel pump or the fuel-pressure regulator is at fault. </li></ul>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.
<ul><li>Leaking injectors may be found by disabling the ignition, unhooking all injectors, and checking exhaust for hydrocarbons (HC) using a gas analyzer while cranking the engine (maximum HC = 300 ppm). </li></ul>Quick and Easy Leaking Injector Test
SCAN TOOL VACUUM LEAK DIAGNOSIS <ul><li>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: </li></ul>Continued <ul><li>Idle speed increases due to the extra air just as if the throttle pedal was depressed. </li></ul><ul><li>The MAP sensor reacts to the increased air from the vacuum leak as an additional load on the engine. </li></ul><ul><li>The computer increases the injector pulse width slightly longer due to the signal from the MAP sensor. </li></ul><ul><li>The air–fuel mixture remains unchanged. </li></ul><ul><li>Idle air control (IAC) counts will decrease, thereby attempting to reduce the engine speed to the target idle speed stored in the computer memory. See Figure 60–6. </li></ul>
Figure 60–6 Using a scan tool to check for IAC counts or percentage as part of a diagnostic routine. Continued
<ul><li>One of the best indicators of a vacuum leak on a speed-density fuel-injection system is to look at the IAC counts or percentage, usually 15 to 25. A reading of less than 5 indicates a vacuum leak. If a vacuum leak occurs on an engine equipped with a mass airflow-type fuel-injection system, the extra air causes the following: </li></ul>Continued <ul><li>The engine will operate leaner-than-normal because the extra air has not been measured by the MAF sensor. </li></ul><ul><li>The idle speed will likely be lower due to the leaner-than-normal air–fuel mixture. </li></ul><ul><li>The idle air control (IAC) counts or percentage will often increase in an attempt to return the engine speed to the target speed stored in the computer. </li></ul>
<ul><li>Most electronic fuel-injection computer systems use the ignition primary (pickup coil or crank sensor) pulse as the trigger for when to inject (squirt) fuel from the injectors (nozzles). If this signal were not present, no fuel would be injected. Because this pulse is also necessary to trigger the module to create a spark from the coil, it can be said that “no spark” could also mean “no squirt.” If the cause of a no-start condition is observed to be a lack of fuel injection, do not start testing or replacing fuel-system components until the ignition system is checked for proper operation. </li></ul>No Spark, No Squirt
PORT FUEL INJECTION SYSTEM DIAGNOSIS <ul><li>To determine if a port fuel-injection system—including the fuel pump, injectors, and fuel-pressure regulator—is operating correctly: </li></ul><ul><li>Attach a fuel-pressure gauge to the Schrader valve on the fuel rail. </li></ul>Figure 60–7 Checking the fuel pressure using a fuel pressure gauge connected to the Schrader valve. Continued <ul><li>Turn the ignition key on or start the engine to build up the fuel-pump pressure (to about 35 to 45 psi). </li></ul>
<ul><li>Wait 20 minutes and observe the fuel pressure retained in the fuel rail and note the psi reading. The fuel pressure should not drop more than 20 psi (140 kPa) in 20 minutes. </li></ul>Continued <ul><li>The check valve in the fuel pump </li></ul><ul><li>Leaking injectors, lines, or fittings </li></ul><ul><li>A defective (leaking) fuel-pressure regulator </li></ul>To determine which unit is defective, perform the following: <ul><li>Reenergize the electric fuel pump. </li></ul><ul><li>Clamp the fuel supply line, and wait 10 minutes. If the pressure drop does not occur, replace the fuel pump. If the pressure drop still occurs, continue with the next step. </li></ul>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:
<ul><li>Repeat the pressure buildup of the electric pump and clamp the fuel return line. If the pressure drop time is now okay, replace the fuel-pressure regulator. </li></ul><ul><li>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. </li></ul>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 <ul><li>One of the first checks to perform when diagnosing a no-start condition is whether the fuel injectors are being pulsed by the computer. Proper pulsing of the injector is also important in diagnosing a weak or dead cylinder. A noid light is designed to electrically replace the injector in the circuit and to flash if the injector circuit is working correctly. </li></ul>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).
<ul><li>To use a noid light, disconnect the electrical connector at the fuel injector and plug the light into the injector harness connections. Crank or start the engine. The noid light should flash regularly. </li></ul>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)
<ul><li>Possible noid light problems and causes include the following: </li></ul>Continued <ul><li>The light is off and does not flash The problem is an open in either the power side or ground side (or both) of the injector circuit. </li></ul><ul><li>The noid light flashes dimly A dim noid light indicates excessive resistance or low voltage available to the injector. Both the power and ground side must be checked. </li></ul><ul><li>The noid light is on and does not flash If the noid light is on, then both a power and a ground are present. Because the light does not flash (blink) when the engine is being cranked or started, then a short-to-ground fault exists either in the computer itself or in the wiring between the injector and the computer. </li></ul>
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 <ul><li>The electrical balance test involves measuring the injector coil-winding resistance. For best engine operation, all injectors should have the same electrical resistance. </li></ul>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.
<ul><li>Measure resistance of all injectors. Replace any that do not fall within the resistance range of the specification. </li></ul>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.
<ul><li>If any injector measures close to specification, make certain that the terminals of the injector are electrically sound, and perform other tests to confirm an injector problem before replacement. </li></ul>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.
<ul><li>Many vehicles are equipped with a port fuel-injection system that “fires” two or more injectors at a time. A V-6 may group all three injectors on one bank to pulse on at the same time. Then the other three injectors will be pulsed on. This sequence alternates. 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. </li></ul>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. <ul><li>A V-6 has two groups of three injectors. If both groups measure 4 ohms, it is likely all six injectors are OK. However, if one group measures only 2.9 ohms and the other measures 4 ohms, it is likely one or more fuel injectors are defective (shorted). </li></ul>
<ul><li>The first test is to measure the resistance of the coil inside and compare it to factory specs. If the injectors are not accessible, check service information for the location of the electrical connector for the injectors. </li></ul>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.
<ul><li>All fuel injectors should measure the specified resistance. However the specification often indicates the temperature of the injectors be at room temperature and of course will vary according to the temperature. Rather than waiting for all of the injectors to achieve room temperature, measure the resistance and check that they are all within 0.4 ohm of each other. To determine the difference, record the resistance of each injector and then subtract the lowest resistance reading from the highest resistance reading to get the difference. If more than 0.4 ohm then further testing will be needed to verify defective injector(s). </li></ul>Equal Resistance test
PRESSURE DROP BALANCE TEST <ul><li>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. Most manufacturers recommend that the pressures be within about 1.5 psi (10 kPa) of each other for satisfactory engine-performance. This test method not only tests the electrical functioning of the injector (for definite time and current pulse), but also tests for mechanical defects that could affect fuel flow amounts. </li></ul>Continued
<ul><li>The purpose of running this injector balance test is to determine which injector is restricted, inoperative, or delivering fuel differently than the other injectors. Replacing a complete set of injectors can be expensive. The basic tools needed are: </li></ul>Continued <ul><li>Accurate pressure gauge with pressure relief </li></ul><ul><li>Injector pulser with time control </li></ul><ul><li>Necessary injector connection adapters </li></ul><ul><li>Safe receptacle for catching and disposing of any fuel released </li></ul>
<ul><li>The testing procedure: </li></ul>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
<ul><li>Step #6 Reenergize the fuel pump and repeat this procedure for all of the engine injectors. Step #7 Compare the two pressure readings and compute the pressure drop for each injector. Compare the pressure drops of the injectors to each other. Any variation in pressure drops will indicate an uneven fuel delivery rate between the injectors. </li></ul>See the chart on Page 725 of your textbook.
INJECTOR VOLTAGE DROP TESTS <ul><li>This test involves pulsing the injector and measuring the voltage drop across the windings as current is flowing. A typical voltage-drop tester is shown here. </li></ul>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.
<ul><li>This which will display the voltage drop as the current flows through the winding. Record the highest voltage drop observed on the meter display during the test. Repeat the voltage-drop test for all of the injectors. The voltage drop across each injector should be within 0.1 volt of each other. If an injector has a higher-than-normal voltage drop, the injector windings have higher-than-normal resistance. </li></ul>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 <ul><li>A scope (analog or digital storage) can be connected into each injector circuit. There are three types of injector drive circuits, each with its own characteristic pattern. </li></ul>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.
<ul><li>Saturated Switch Type In a saturated switch-type injector-driven circuit, voltage (usually a full 12 volts) is applied to the injector. Ground for the injector is provided by the vehicle computer. Due to the resistance and inductive reactance of the coil itself, it requires a fraction of a second (about 3 milliseconds or 0.003 seconds) for the coil to reach saturation or maximum current flow. Most saturated switch-type fuel injectors have 12 to 16 ohms of resistance. This resistance, as well as the computer switching circuit, control and limit the current flow through the injector. A voltage spike occurs when the computer shuts off (opens the injector ground-side circuit) the injectors. See Figure 60–18. </li></ul>Continued
Figure 60–18 The injector on-time is called the pulse width. Continued
<ul><li>Peak-and-Hold Type A peak - and - hold type is typically used for TBI and some port low-resistance injectors. Battery voltage is applied to the injector and the ground side is controlled through the computer. The computer provides a high initial current flow (about 4 amps) to flow through the injector windings to open the injector core, then reduces the current to a lower level (about 1 amp). Typical peak-and-hold-type injector resistance ranges from 2 to 4 ohms. The scope pattern of a typical peak-and-hold-type injector shows the initial closing of the ground circuit, then a voltage spike as the current flow is reduced. Another voltage spike occurs when the lower level current is turned off (opened) by the computer. See Figure 60–19. </li></ul>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
<ul><li>Pulse-Width Modulated Type A pulse-width modulated type of injector drive circuit uses lower-resistance coil injectors. Battery voltage is available at the positive terminal of the injector and the computer provides a variable-duration connection to ground on the negative side of the injector. The computer can vary the time intervals that the injector is grounded for very precise fuel control. Each time the injector circuit is turned off (ground circuit opened), a small voltage spike occurs. It is normal to see multiple voltage spikes on a scope connected to a pulse-width modulated type of fuel injector. </li></ul>Continued
<ul><li>This is a good question. Many service techs “recommend” that the three good injectors also be replaced along with the three tested defective. The reasons given include: </li></ul><ul><li>With these ideas in mind, the customer should be informed and offered the choice. Complete sets of injectors such as those in can be purchased at a reasonable cost. </li></ul>If Three of Six Injectors Are Defective, Should I Also Replace the Other Three? <ul><li>All six injectors have been operating under the same fuel, engine, and weather conditions. </li></ul><ul><li>The labor required to replace all six is just about the same as replacing only the three defective injectors. </li></ul><ul><li>Replacing all six helps ensure that all the injectors are flowing the same amount of fuel so the engine is operating most efficiently. </li></ul>
IDLE AIR SPEED CONTROL DIAGNOSIS <ul><li>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. </li></ul>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.
<ul><li>When the engine stops, most IAC units will retract outward to get ready for the next engine start. When the engine starts, the engine speed is high to provide for proper operation when the engine is cold. As the engine gets warmer, the computer reduces idle speed gradually by reducing the counts or steps commanded by the IAC. </li></ul>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.
<ul><li>An intermittent “check engine” light and a random-misfire diagnostic trouble code (DTC) P0300 was being diagnosed. A scan tool did not provide any help because all systems seemed to be functioning normally. Finally, the technician removed the engine cover and discovered a mouse nest. </li></ul>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 <ul><li>Some techs still misunderstand the process of proper fuel-system handling. Some manufacturers have suggested methods, while others have issued bulletins to prohibit any cleaning at all. All engines using fuel injection do require some type of fuel-system maintenance. Normal wear and tear with today’s underhood temperatures and changes in gasoline quality contribute to the buildup of olefin wax, dirt, water, and many other additives. Unique to each engine is an air-control design that also may contribute different levels of carbon deposits, such as oil control. </li></ul>Continued
<ul><li>Fuel-injection system service should include the following: </li></ul>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
<ul><li>2. Test the fuel - pressure regulator for operation and leakage This works well as the operator has total control of rail pressure with a unit control valve. Below are some points to consider: </li></ul>Continued <ul><li>Good pressure does not mean proper volume. A clogged filter may test okay on pressure but the restriction may not allow proper volume under load. See Figure 60–26. </li></ul><ul><li>It is a good idea to use the vehicle’s own gasoline to service the system versus a can of shop gasoline that has been sitting around for some time. </li></ul><ul><li>Pressure regulators do fail and a lot more do not properly shut off fuel, causing higher-than-normal pump wear and shorter service life. </li></ul>
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.
<ul><li>3. Flush the entire fuel rail and upper fuel - injector screens including the fuel - pressure regulator . Raise the input pressure to a point above regulator setting to allow a constant flow of fuel through the inlet pressure side of the system, through the fuel rail, and out the open fuel-pressure regulator. In most cases the applied pressure is 75 to 90 psi, (517 to 620kPa) but will be maintained by the presence of a regulator. At this point, cleaning chemical is added to the fuel at a 5:1 mixture and allowed to flow through the system for 15 to 30 minutes. Results are best on a hot engine with the fuel supply looped and the engine not running. </li></ul>Continued
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.
<ul><li>This flush is the fix most vehicles need first. The difference is that the deposits are removed to a remote tank and filter versus attempting to soften the deposits and blow them through the upper screens. </li></ul><ul><li>Most injectors use a 10-micron final filter screen. A 25% restriction in the upper screen would increase the injector on-time approximately 25%. </li></ul><ul><li>Clean the fuel injectors Adjust output pressure closer to regulator pressure or lower than in previous steps. Lower pressure will cause the pulse width to open up longer and allow the injectors to be cleaned. Clean injectors are the objective, but the chemical should also decarbon the engine valves, pistons, and oxygen sensor. </li></ul>Continued More items to consider:
<ul><li>4. Decarbon the engine assembly . On most vehicles, the injector spray will help the decarboning process. On others, you may need to enhance the operation with external addition of a mixture through the PCV hose, throttle plates, or idle air controls. </li></ul>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.
<ul><li>5. Clean the throttle plate and idle air control passages . Doing this service alone on most late-model engines will show a manifold vacuum increase of up to 2 in. Hg. </li></ul>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.
<ul><li>6. Relearn the onboard computer . Some vehicles may have been running in such a poor state of operation the onboard computer may need to be relearned. Consult service information for the suggested relearn procedures. </li></ul>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
<ul><li>Whenever you service the fuel injectors, or if you suspect that there may be a fuel-injector problem, remove the entire fuel rail assembly and check the passages for contamination. Always thoroughly clean the rail when replacing fuel injectors. </li></ul>Be Sure To Clean the Fuel Rail
FUEL SYSTEM SCAN TOOL DIAGNOSTICS <ul><li>Diagnosing a faulty fuel system can be a difficult task that can be made easier by utilizing the information available via the serial data stream. </li></ul><ul><li>Observing the long-term fuel trim and the short-term fuel trim can help determine how the fuel system is performing. Short-term fuel trim and long-term fuel trim can help us to zero in on specific areas of trouble. Readings should be taken at idle and at 3000 rpm. </li></ul><ul><li>Use the chart following. </li></ul>Continued
SUMMARY <ul><li>A typical throttle-body fuel injector uses a computer-controlled injector solenoid to spray fuel into the throttle-body unit above the throttle plates. </li></ul><ul><li>A typical port fuel-injection system uses an individual fuel injector for each cylinder and squirts fuel directly into the intake manifold about 3 inches (80 millimeters) from the intake valve. </li></ul><ul><li>A typical fuel-injection system fuel pressure should not drop more than 20 psi in 20 minutes. </li></ul><ul><li>A noid light can be used to check for the presence of an injector pulse. </li></ul>Continued
SUMMARY <ul><li>Injectors can be tested for resistance and should be within 0.3 to 0.4 ohms of each other. </li></ul><ul><li>Different designs of injectors have a different scope waveform depending on how the computer pulses the injector on and off. </li></ul><ul><li>An idle air control unit controls idle speed and can be tested for proper operation using a scan tool or scope. </li></ul>( cont. )