Fuel Injection System - Honda Pgm-Fi Honda Prelude II

DESCRIPTION

There are 4 sub-systems in the PGM-FI (Programmed Fuel-Injection) system: air intake system, electronic control system, idle control system, and fuel delivery system. The electronic control system is covered in the COMPUTER CONTROLS section. The idle control system is covered in the TUNE-UP section. The other 2 systems, air intake and fuel delivery, are covered here.

The system uses an 8-bit microcomputer and various sensors to provide accurate control of air/fuel mixture under all operating conditions. At the precise time a piston is on its intake stroke, fuel is injected into the correct intake manifold runner (sequential injection).

PGM-FI Schematic. Scheme 35

ELECTRIC FUEL PUMP

The fuel pump is an in-line, direct drive type. Fuel is drawn into the pump through a filter, flows around the armature through a one-way valve and is delivered to the engine compartment. A baffle is provided to prevent fuel pulsation.

The fuel pump has a relief valve to prevent excessive pressure. It opens if there is a blockage in the discharge side. When the relief valve opens, fuel only flows from the high pressure side to the low pressure side. A check valve is used to maintain fuel pressure in the line after the pump is stopped to ease re-starting.

The pump consists of a rotor, rollers and pump spacer. (Scheme 36) When the rotor turns, the rollers turn and travel along the inner surface of the pump spacer by centrifugal force. The volume of the cavity enclosed by these 3 parts changes, drawing and pressurizing fuel.

Electric Fuel Pump. Scheme 36

FUEL PRESSURE REGULATOR

The fuel pressure regulator maintains constant fuel pressure to the injectors. The spring chamber of the regulator is connected to the intake manifold to constantly maintain fuel pressure at 36 psi (2.55 kg/cm 2 ) higher than the pressure in the manifold. When the difference between the fuel pressure and manifold pressure exceeds 36 psi (2.55 kg/cm 2 ), the diaphragm is pushed upward, and the excessive fuel is fed back into the fuel tank through the return line.

Pressure Regulator Assembly. Scheme 37

FUEL INJECTOR

The injector is of the solenoid actuated constant-stroke type consisting of a solenoid, plunger, needle valve and housing. When current is applied to the solenoid coil, the valve lifts up and pressurized fuel fills the inside of the injector and is injected close to the intake valve. Because the needle valve lift and fuel pressure are constant, the injection quantity is determined by the length of time that the valve is open (i.e., the duration the current is supplied to the solenoid coil). The injector is sealed by an "O" ring and seal ring at the top and bottom. These seals also reduce operating noise.

Fuel Injector Assembly. Scheme 38

RESISTOR

To prolong injector life, flow of electrical current to the injector coil is restricted by a resistor installed in series between the electrical power source and the injector coil.

MAIN RELAY

The main relay is a direct-coupler type. It contains relays for the ECU power supply and the fuel pump power supply. This relay is installed at the left side of the cowl.

ELECTRONIC CONTROL UNIT

The ECU contains memories for basic injector discharge durations at various engine speeds and manifold pressures. Basic injector discharge duration, after being read out from the memory, is further modified by signals sent from various sensors to obtain the final discharge duration. Some other functions include starting control, fuel pump control, fuel cut-off control and a fail-safe system monitor.

At start-up, air/fuel ratio must be enriched. The ECU memories contain basic discharge durations to be read out by signals from the starter switch, engine speed and coolant temperature sensors. This provides extra fuel needed for start-up.

When engine speed falls below 100 RPM, electric current to the fuel pump is cut off, preventing injectors from discharging fuel. During deceleration with the throttle valve nearly closed, electric current to the injectors is cut off at speeds over 1200 RPM, contributing to improved fuel economy. Fuel cut off action also takes place when engine speed exceeds 6600 RPM, regardless of the position of the throttle valve.

A fail-safe system monitors sensors and detects any abnormalities in the ECU, ensuring safe driving even if one or more sensors are faulty, or if the ECU malfunctions.

DASHPOT

A dashpot is used to slow the throttle closing of the throttle valve as it suddenly approaches the closed position during gear shifting or deceleration. When the throttle is in the closed position, the throttle valve contacts the throttle stop screw.

THROTTLE CABLE

Check that the throttle cable operates smoothly with no binding or sticking. Repair as necessary. Check cable free play at the throttle linkage. Cable deflection should be .39-47" (10-12 mm). If deflection is not within specifications, loosen the locknut and turn the adjusting nut until the deflection is as specified. With the cable properly adjusted, check the throttle valve to be sure it opens fully when the accelerator pedal is pushed to the floor. Also check the throttle valve to be sure it returns to the idle position whenever the accelerator is released.

THROTTLE BODY

1. Start the engine and allow to reach normal operating temperature (cooling fan comes on). Disconnect the vacuum hose (to the canister) from the top of the throttle body. Connect a vacuum gauge to the throttle body. Allow the engine to idle and check that the gauge indicates no vacuum. Check that vacuum is indicated on the gauge when the throttle is slightly off idle.
2. If the gauge indicates no vacuum, check the canister port. If the canister port is clogged, clean it with carburetor cleaner. Stop the engine and check that the throttle cable operates smoothly without binding or sticking.
3. If there are any abnormalities, check for excessive wear or play in the throttle valve shaft, sticky or binding throttle lever at fully closed position, or clearance between throttle stop screw and throttle lever at fully closed position. Replace the throttle body if there is excessive play in the throttle valve shaft or if the shaft is binding or sticking. To clean clogged ports, use a commercially available carburetor cleaner.

Checking Throttle Body Assembly. Scheme 39

TESTING

Note. Before starting testing or troubleshooting, check that other items that affect engine performance are within specifications. Check valve clearance, air cleaner and PCV valve. In addition, check ignition timing, function of the vacuum and centrifugal advance, and condition of the spark plugs. It is also necessary to obtain System Checker Harness (07999-60000) to perform some tests.

Retrieving Codes

The PGM-FI system's ECU is equipped with a self-diagnosis function. When an abnormality is detected, the PGM-FI warning light in the instrument panel comes on, and the self-diagnosis indicator in the ECU blinks. The LED on the body of the ECU will blink up to 13 times with a two second pause to indicate trouble codes. The warning light on the instrument panel will shut off when the ignition switch is off, codes will be stored in the ECU. If the problem persists, dashboard warning light will come on again.

If LED fails to light, check for blown Hazard fuse or open circuit in White/Yellow wire between ECU A17 terminal and Hazard fuse. If these check out, replace ECU. With ignition ON, warning light should come on for about 2 seconds. If lamp does not light, check for blown No. 5 fuse, open circuit in Yellow wire between No. 5 fuse and combination meter, open circuit in Green/Red wire between combination meter and control unit, open in Black wires between ECU A2, A4 and Ground 1 or blown warning light bulb.

TROUBLESHOOTING CODE CHART

Clearing Codes

After making repairs, disconnect the negative battery cable for at least 10 seconds, the reconnect and run the engine for a few minutes (if possible) and recheck the LEDs. If the LED pulses the same number of times as before, begin system troubleshooting. If LED does not pulse, a bad connection was at fault.

DASHPOT SYSTEM

1. Slowly open throttle arm until dash pot rod is fully extended. Release throttle arm and measure time until throttle arm contacts stop screw. Time should be less than 2 seconds.
2. If time is over 2 seconds, replace dashpot check valve and retest. If rod does not operate, check for bound linkage, or for clogged check valve or vacuum line. If they are okay, replace dashpot.

RELIEVING FUEL PRESSURE

Note. Before disconnecting fuel pipes or hoses, release pressure from system by loosening 6 mm service bolt located at top of fuel filter.

1. Disconnect battery negative cable. Use a box end wrench on the 6 mm service bolt at top of the fuel filter, while holding banjo bolt with another wrench.
2. Place a rag or shop towel over bolt. Slowly loosen service bolt one complete revolution at a time. Always replace washer between service bolt and banjo bolt whenever service bolt is loosened to relieve fuel pressure. Replace all washers whenever bolts are removed to disassemble parts.

INSPECTING FUEL PRESSURE

1. Relieve fuel pressure. Remove service bolt on top of fuel filter while holding banjo bolt with another wrench and attach fuel pressure gauge. Start engine. Measure fuel pressure with engine idling and pressure regulator vacuum hose disconnected.
2. Pressure should be 36-41 psi (2.55-2.85 kg/cm 2 ). If fuel pressure is not within specifications, first check fuel pump. If pump is okay, check the following: with pressure high, check for pinched or clogged fuel return hose or piping, or a faulty pressure regulator; with pressure low, check for a clogged fuel filter, pressure regulator failure, or leakage in fuel line.

INJECTOR

Note. Check idle speed, ignition timing, valve clearance and idle CO % before performing test.

Engine Runs

1. With engine idling, disconnect injector couplers and note change in idle speed. If idle speed drop is consistent for all injectors, injectors are normal. If idle speed or quality remains the same when a particular injector is disconnected, replace that injector and re-test.
2. Also, check for a clicking sound of each injector using a stethoscope during engine idle. If any injector fails to emit typical clicking sound, check wiring between ECU and injector. If necessary, replace injector.

Engine Will Not Run

1. Remove injector connector and measure resistance between 2 terminals of injector. Resistance should be 1.5-2.5 ohms. If resistance is not within specifications, replace injector. If resistance is as specified, check fuel pressure.
2. If fuel pressure is as specified, check whether there is any short-circuiting, wire breakage or poor connections in wire between main relay and resistor. Check whether resistor is open or corroded. Check whether there is any short-circuiting, wire breakage, or poor connections in the wire between resistor and injector. Check whether there is any short-circuiting, wire breakage or poor connections in wire between injector and ECU. If all is okay, check the ECU.

FUEL SYSTEM RESISTOR

Disconnect resistor coupler. Check resistance between all resistor terminals, and power terminal (A). (Scheme 40) Resistance should read 5-7 ohms. Replace resistor if any resistance readings are out of specified range.

Testing Fuel System Resistor. Scheme 40

PRESSURE REGULATOR

Note. If fuel pressure is does not meet specifications 36-41 psi (2.55-2.85 kg/cm 2 ), check fuel pump first, then pressure regulator.

Check for pinched, cracked, blocked or broken vacuum hoses. Check that fuel pressure rises by disconnecting vacuum hose at pressure regulator. If fuel pressure does not rise, pinch return hose 2 or 3 times. If fuel pressure is not within specifications, replace regulator.

1. Remove main relay located near fuse box at side cowl. Connect battery positive terminal to No. 4 terminal and battery negative terminal to No. 8 terminal of main relay. Check continuity between terminal No. 5 and terminal No. 7. If there is no continuity, replace main relay.
2. Connect battery positive terminal to No. 5 terminal and battery negative terminal to No. 2 terminal of main relay. Check for continuity between terminal No. 1 and terminal No. 3. If there is no continuity, replace main relay.
3. Connect battery positive terminal to terminal No. 3 and battery negative terminal to terminal No. 8 of main relay. Check for continuity between terminal No. 5 and terminal No. 7 of main relay. If there is no continuity, replace main relay. If main relay is okay, but fuel pump still does not work, proceed to «HARNESS TESTING»(/honda/prelude/ii-1983-1987/remont/testing-diagnostics/#fuel-injection-system-honda-pgm-fi). (Scheme 41)

Testing Main Relay. Scheme 41

Scheme 42

1. With ignition switch off, disconnect main relay coupler. Connect positive probe of voltmeter to wire No. 1 in coupler and negative probe to body ground. Battery voltage should be available. (Scheme 42) (Scheme 42): Testing Main Relay Wire Harness
2. If there is no voltage, check wiring harness between battery and main relay as well as ECU fuse which is located in engine compartment.
3. Connect positive terminal of voltmeter to wire No. 5 of main relay coupler and negative probe to body ground. Turn ignition on. Battery voltage should be indicated. If there is no voltage, check wiring from ignition switch and main relay as well as fuse No. 4.
4. Connect positive probe of voltmeter to wire No. 4 of main relay coupler and negative probe to body ground. Turn ignition switch to "START" position. Battery voltage should be indicated. If there is no voltage reading, check wiring between ignition switch and main relay as well as fuse No. 1.
5. Connect a jumper wire between wire No. 1 and wire No. 7 of main relay coupler. Fuel pump should operate. If fuel pump does not operate, check wiring between battery and fuel pump and wiring from fuel pump to ground (Black wire).

FUEL CUT-OFF SYSTEM

1. Start engine and bring up to normal operating temperature. Ensure that engine idles smoothly. On vehicles equipped with man. trans., disconnect vacuum hose from dashpot. Using a stethoscope, touch the tip to the injector and confirm injector operation.
2. While listening to an injector, increase engine to 3000 RPM then release the throttle. Clicking of injectors should cease momentarily when throttle is released. If clicking does not cease, check ECU, throttle angle sensor, or wiring between injector and ECU.

FUEL PUMP

Scheme 43

1. With ignition off, disconnect coupler from main relay which is located behind fuse box. Using a jumper, connect wires as shown. (Scheme 43) Relieve fuel pressure. Disconnect fuel return pipe from regulator. (Scheme 43): Testing Fuel Pump
2. Turn ignition on and measure amount of fuel flow for 10 seconds, then turn ignition off. Amount should be 7.8 oz. (230 cc) minimum in 10 seconds at 12 volts.
3. If fuel flow is less than specified, check for fuel pump failure, clogged fuel filter, clogged fuel line, or faulty pressure regulator.
4. If fuel pump problems are suspected, ensure that fuel pump actually runs. It should emit noise when on. If pump does not make noise, run check as outlined in steps 5) and 6).
5. Jack up vehicle and support properly on stands. Remove left rear wheel. Remove fuel pump cover and disconnect Yellow and Black wires. CAUTION: Be sure to turn ignition switch off before disconnecting wires.
6. Check that battery voltage is available at fuel pump wire couplers when ignition switch is on. To do so, connect positive probe of voltmeter to Yellow wire and negative probe to Black wire.
7. If battery voltage is available, replace fuel pump. If there is no voltage, check main relay and wire harness.

Removal

Disconnect PCV hose from intake air boot. Remove intake air boot clamp at throttle body. Disconnect electrical lead from throttle angle sensor. Disconnect all hoses and vacuum lines at throttle body. Remove mounting nuts and remove throttle body from intake manifold.

Installation

To install, reverse removal procedure. Ensure proper routing of all hoses, vacuum lines and electrical leads. Make necessary idle adjustments.

1. Disconnect negative battery cable. Relieve fuel pressure. Disconnect coupler at injector. Disconnect vacuum hose and fuel return line from pressure regulator.
2. Place a rag or shop towel over hose and tube before disconnecting them. Loosen retainer nuts. Disconnect fuel rail. Remove injector from intake manifold.

1. Slide NEW cushion rings onto injector. Coat new rings with clean engine oil and put them on injectors. Insert injectors into fuel rail. Coat NEW seal rings with clean engine oil and press them into intake manifold. CAUTION: To prevent damage to "O" ring, insert injector into fuel rail squarely and carefully. Install injectors into fuel rail first, then install them into intake manifold.
2. Tighten retainer nuts. Connect vacuum hose and fuel return hose to pressure regulator. Install couplers onto injectors. Turn ignition switch to "ON" position but DO NOT operate starter.
3. After fuel pump runs for approximately 2 seconds, fuel pressure in fuel line rises. Repeat this procedure 2 or 3 times. Then, check for any fuel leaks.

1. Jack up vehicle and support on stands. Remove left rear wheel. Remove fuel pump cover. Remove 3 bolts, then remove pump with its mount. Disconnect fuel lines and electrical leads.
2. Remove clamp and then remove fuel pump. Remove fuel line and damper from pump. DO NOT disassemble fuel pump.

1. Install new fuel pump on its mount. Carefully clean sealing surface of flared fuel line, then install it on fuel pump and tighten flare nut. Reinstall fuel hose and damper on front of pump.
2. Reconnect electrical leads and reinstall fuel pump. Have an assistant turn ignition switch to "ON" position while watching fuel pump connections for leaks. Repeat check 2 or 3 times to ensure there are no fuel leaks.

EFI Wiring Diagram (Prelude). Scheme 44

See also:
• HARNESS TESTING