Fuel Injection System - Bosch LH Volvo 240 I

DESCRIPTION

The 1986 Bosch LH-Jetronic fuel injection system integrates the fuel injection and idle speed control functions into one system. One electronic control unit (ECU) controls all system functions.

The LH Jetronic fuel injection system operates with moderate fuel pressure, held constant by a line pressure regulator. Fuel is metered into the cylinders by electrically controlled solenoid valves in the injectors. The injectors are installed just ahead of each cylinder intake valve.

Actual duration of injection (2-12 milliseconds), is determined by the ECU. The ECU receives several signals on various driving, engine and outside conditions from a set of sensors and an air mass meter.

Signals from air mass meter and exhaust gas oxygen sensor provide most of the information used by the electronic control unit maintain proper air/fuel ratios. An idle speed adjustment screw is located on throttle housing.

ELECTRONIC CONTROL UNIT (ECU)

The ECU is a microprocessor based computer that receives and evaluates readings from various sensors. The control unit then produces a signal that is sent to each injector to ensure the correct amount of fuel delivery for all operating conditions. Located in the right kick panel, it also controls the Constant Idle Speed system.

FUEL SYSTEM

The fuel system consists of a fuel tank, a fuel feed pump, fuel lines, in-line fuel pump, filter, and a line pressure regulator. Fuel is supplied to each injector at a constant pressure. Only fuel injection duration is varied (to meet changing engine requirements).

The fuel feed pump is an electrically operated vane pump. The pump is near bottom of fuel tank. Fuel is strained through a mesh screen before entering fuel pump. There is a check valve on outlet side of pump to prevent fuel supply from draining back into tank.

The fuel feed pump supplies fuel from the tank to a pressurized container. The main, electrically-driven rotary pump draws pressurized fuel from the container and delivers it to the fuel injection manifold. Because the main pump always draws pressurized fuel, air is unable to enter fuel system. The fuel filter is attached to a bracket located underneath the vehicle.

The main fuel pump and filter are attached to a bracket located underneath the vehicle, under the left rear seat. This electrically-operated roller pump draws fuel from tank and delivers it to the fuel injection manifold.

The pump is equipped with a check valve to prevent back flow. Both types off main pumps also have an overpressure relief valve which opens if fuel system becomes clogged and pressure rises too high.

INJECTORS

The injectors, located in intake manifold, point directly toward intake valve. All injectors are supplied with fuel from a common fuel manifold. The injection pulse is controlled electrically by a needle valve in lower section of injector. The needle valve is operated by an electric solenoid which is switched on and off by the ECU.

FUEL PUMP RELAY

The fuel pump relay is located on firewall under instrument panel. The system relay and fuel pump relay are located together on a holder near ECU. This relay energizes fuel feed pump and main fuel pump.

Air Mass Meter

The air mass meter continually measures temperature, amount, density, and speed of air entering engine intake system. The meter consists of a platinum wire filament located within intake air stream, and a circuit board with a CO adjustment potentiometer.

The wire filament sends a temperature related signal to the circuit board for processing. Once processed, airflow signal is sent to ECU.

Over a period of time, the filament can become coated with dirt or other contaminants. To prevent this, the filament is automatically heated to a high temperature for about 1 second, each time engine is shut off.

A/C Micro Switch

The switch closes when A/C is engaged. The ECU will then increase idle speed to compensate for greater engine load.

Oxygen Sensor

The oxygen sensor checks exhaust gas for presence of unburned oxygen. Unburned oxygen in exhaust gas indicates incomplete combustion due to improper mixture, spark timing or other conditions. The oxygen sensor is located in exhaust manifold.

Throttle Valve Switch

The throttle valve switch consists of double micro-switch. One switch is activated at idle, the other during "full-load" conditions. The switch is located on side of throttle housing.

Coolant Temperature Sensor

The coolant temperature sensor is located in the cylinder head. This sensor provides ECU with an engine temperature signal. This sensor also operates the temperature gauge.

Engine Speed

The engine speed signal is generated by an electronic (Hall Effect) ignition distributor. The low voltage ignition primary pulses are monitored at low tension side of ignition coil. Injection timing is regulated by this signal.

SYSTEM RELAY

The system relay is located on firewall under instrument panel, next to fuel pump relay. This relay provides current to the ECU. It is energized during filament burn off after ignition has been switched off.

FUSES, GROUND CONNECTIONS & CONNECTORS

1. Check ground connections on inlet manifold. Make sure wires are correctly connected and not loose. Poor connections can cause many fault symptoms.
2. Check fuses for pump relay and tank pump. The pump relay fuse is an in-line fuse in the engine compartment. There are two of them. The tank pump fuse is fuse no. 4 and is in the fuse box.
3. Check the connectors for the air mass meter, air control valve, knock sensor and coolant temperature sensor. Make sure connectors are correctly connected and not loose.
4. Make sure that the knock sensor and coolant temperature sensor connectors are not interchanged. The knock sensor wires are green and the coolant temperature sensor wires are yellow.

AIR LEAKAGE, THROTTLE SWITCH, IDLE SPEED

1. Check the induction system for leakage. If air leaks from point where air mass meter is mounted on engine, air-fuel mixture will be lean. Check the inlet system between air mass meter and intake manifold. Check all the hose and connections on the intake manifold. Check the couplings and seals for intake manifold, throttle housing, etc.
2. Check the throttle housing for dirt. To clean the throttle housing, disconnect the connector from the throttle switch. Remove throttle housing and clean it with a suitable solvent. Keep throttle switch dry. Remember that a dirty throttle housing indicates a blocked, incorrectly fitted or damaged air fitler.
3. Install the throttle housing. Use a new gasket. Connect hoses and throttle switch connector.
4. Adjust the throttle by loosening the screws at throttle valve switch and loosen the lock nut. Unscrew the adjustment screw until throttle is fully closed. Screw in the adjustment screw until it just contacts link arm and then a further 1/2 turn. Retighten the nut, making sure that the adjustment screw does not turn at the same time.
5. Check the throttle switch. Open the throttle slightly and listen. A click should be heard as soon as the throttle is opened to indicated that the idle switch opens. To adjust the throttle switch, loosen the screws (Allen key 3mm). Turn switch clockwise slightly, then turn switch back until a click is heard. Tighten retaining screws. Check setting.
6. Check the idle speed.

Note. The engine should be warmed up until radiator thermostat opens and then for a further 10 minutes.

Connect a tachometer. Ground the blue-white wire from test point to close air control valve.

Note. Switch off A/C as applicable

Ajdust engine speed w/idle adjustment screw at 700 RPM. Disconnect ground wire from test point. Engine speed should increas to 750 +/- 20 RPM.

Note. It is occasionally necessary to slacken throttle switch to obtain correct setting.

Adjust engine controls. See THROTTLE VALVE, SWITCH, LINKAGE ADJUSTING.

FUEL LINE PRESSURE/PRESSURE VALVE

1. Connect pressure gauge 5011 (Scheme 20) Turn ingintion off. Hold a piece of absorbent paper underneath fuel line to prevent spillage. Connect gauge between fuel line and fuel distribution rail. Use hose 5116 and adapter 5265 (Scheme 20) Plug gauge hose with 5266 (Scheme 20) Turn gauge cock to position 1 (pointing towards hose 5116) (Scheme 20)
2. Check main fuel pump and tank pump. Remove panel from right-hand of footwell. Disconnect main relay. Connect a bridge wire across terminals 30 and 87/2 (Scheme 21) Fuel pump is easiest to hear. To check tank pump, remove fuel tank lid and listen.
3. If neither pump operates, disconnect bridge wire from terminals 30 and 87/2 (Scheme 21) Check for voltage at terminal 30. If there is no voltage, check fuse and wire between battery and relay. Connect a bridge wire from terminals 30 and 87/2 (Scheme 21) Both pumps should start. If pumps do not start, check wires between relay pumps. If one of the pumps operates, check wiring from fusebox to defective pump. Install a new pump if wiring is OK.
4. Measure line pressure, it should be 36 psi. If the Line pressure is too high, then disconnect the wire connected between the fuel pump relay connections 30 and 87/2 (Scheme 21) Disconnect the fuel return line from pressure regulator. Blow through the line. Disconnect vacuum hose from pressure regulator. Blow through the line. If both hoses are free from blockages, regulaor is defective and should be replaced. Re-check pressure after installing new regulator. If the pressure is too low, then pinch the fuel return line w/hand and check pressure increase. It is very important to no allow the pressure to exceed 85 psi. If pressure rises quickly, pumps and fuel lines are OK. Replace the regulator and measure again. If pressure rises slowly, this indicates a blocked fuel filter, tank pump filter or fuel line. If pressure does not rise, fuel pump is defective.
5. Check the pressure regulator. Connect a vacuum pump to regulator. Use vacuum pump 5843, or equivalent. (Scheme 22) Pump air out of regulator and check that line pressure drops. Line pressure should drop to same extent as drop in regulator. 36 psi minus vacuum should equal line pressure.
6. Switch off fuel pumps. Disconnect wire between terminals 30 and 87/2 (Scheme 21) Connect the connector to the main relay. Reinstall the panel under the dashboard.
7. Disconnect pressure gauge 5011. Hold a piece of absorbent paper underneath fuel line to prevent spillage. It is important to know that any plastic fuel line ties must be refitted.

Pressure Gauge and Hoses. Scheme 20

Main Fuel Pump Connector Terminals. Scheme 21

Connecting Vacuum Pump to Pressure Regulator. Scheme 22

Scheme 23

1. Turn ignition off and disconnect connector from control unit. Remove panel beneath right side of dashboard, door step molding, protective moling and side panel. Lift catch upward and fold connector downward. CAUTION: Iginition must be off when disconnecting/connecting connector.
2. Remove Plastic cover from connector. CAUTION: Do not insert instrument probe into front of connector. Experience has shown that this can case damage and introduce faults. Check terminals in holes through side of connector. Don't press too hard on terminals, only enough to make good electrical contact. Terminal number is stamped on side of connector.
3. Check ground connections. Connect an ohmmeter between ground and terminals 5, 11, 19, 25 at the ECU. The resistance should be nearly 0 in all cases. Check that resistance is 0 even when the ohmmeter is connected between 11 and 19. Ground wires are connected to intake manifold.
4. Check Lambda sond shielding wire. (Scheme 23) Check that the wire is connected to terminal 5. Check the ground connection between valve cover and firewall.
5. Check that test point is not grounded. Connect ohmmeter between ground and terminal 12 (BL:W), 222. Connect ohmmeter between ground and terminal 22 (P), 149. Resistance should be infinite in both cases.
6. Check the engine speed signal from the ignition system control unit. Connect a voltmeter between ground and terminal 1. Operate starter motor. Voltmeter should give the following readings: Ignition Off equals 0 volts Ignition On equals current from battery (ca 12V) Starter motor in operation equals at least half current from battery.
7. Check current supply. Turn ignition on. Connect a voltmeter between ground and terminal 18. Voltmeter should show battery voltage. Check for voltage when operating starter motor. Turn ignition off.
8. Check fuel injection relay by connecting a voltmeter between ground and control unit terminal 9. Ground terminal 21. Relay should make circuit and meter should show battery voltage. The ground connection at 21 should remain in place.
9. Check air mass meter circuit by moving the rubber cover on air mass meter to one side. Connect a voltmeter between air mass meter terminal 5 and 1. Voltmeter should show battery voltage. Ground terminal 17. Pump relay should activate fuel pumps and pumps should start operating. Connect a voltmeter between ground and terminal 87/2 in main relay. Meter should show battery voltage. Disconnect ground leads from terminal 17 and 21.
10. Check Injector Circuits. Turn ignition off. Connect an ohmmeter between pump relay terminal 87/2 and ECU terminal 13. Correct resistance should be approximately 4 ohms. If meter shows approximately 5.3 ohms, either an injector or injector wire is defective. If meter reads approximately 8 ohms, 2 injectors or injector wires are defective. If meter shows 16 ohms, 3 injectors or injector wires are defective. Injectors may be tested separately. Each injector should have a resistance of 16 ohms.
11. Check air contol valve. Connect an ohmmeter between terminal 87/2 on main relay connector and terminls 23 and 10 on control unit. Resistance should be approximately 20 ohms in both cases at 20°C (68°F).
12. Check preheating resistor in Lambda sond. Connect ohmmeter between ground and terminal 87/2 on main relay connector. Resistance of cold Lambda sond (20°C = 68°F) = 3 ohms. Resistance of warm Lambda sond (above 350°C - 662°F) = 13 ohms. Reconnect the connector.
13. Check air mass meter. Connect ohmmeter between terminals 6 & 7. Resistance should be approx. 3.7 ohms. Connect ohmmeter between 6 & 14. Resistance should be 0 and 1000 ohms depending on position of CO-screw.
14. Check coolant temperature sensor. Connect ohmmeter between ground and terminal 2. Resistance is temperature-dependant. See TEMPERATURE RESISTANCE TABLE for coolant temperature sensor. If incorrect check resistance at sensor to see if fault is due to sensor or wiring. Check ground wire connected to intake manifold. TEMPERATURE RESISTANCE Applciation Ohms -10°C (14°F) 8260-10560 20°C (68°F) 2280-2720 80°C (176°F) 290-364
15. Check throttle switch. Connect ohmmeter between ground and terminal 3. Resistance should be 0. Depress accelerator pedal slightly. Resistance should increase to infinity, switch opens. Connect a voltmeter between ground and terminal 12. Resistance should be infinity, switch open. Depress accelerator pedal slightly. Resistance should decrease to 0, switch closed. If incorrect measure resistance at switch to see if fault is due to switch or wiring. Check ground wire connected to intake manifold.
16. Check assemble connector. CAUTION: Ignition must be off when disconnecting/connecting connector. Connect connector to control unit. Start the engine, if it does not start, then test with a new control unit.
17. Check Lambda sound. Connect CO-meter. Connect meter to adapter next to the catalytic converter. Use 5151. (Scheme 23)WARNING: CO-meter adapter can be extremely hot. (Scheme 23): Meter To Adapter Connection Warm up the engine. Disassemble the Lambda sond connector. Ground the wire that leads to the control unit. CO should increase to show that the wire and control unit are OK. Connect a voltmeter to Lambda sond. Meter should deflect ot show that the Lambda sond functions. If the CO is as specified, the voltage should be approximately 0.5-1.0 volt. Assemble the Lambda sond connector.
18. Check air mass meter burn-off current. NOTE: Engine must be warm. Coolant temperature above 60°C (140°F). Connect a voltmeter between terminals 1 and 4. Increase engine speed to above 2100 rpm. Turn off engine. After 4 seconds meter pointer should deflect for 1 second. Disconnect voltmeter. Refit rubber cover. Disconnect CO-meter. WARNING: CO-meter adapter can be extremely hot. If no faults are found during fault tracing procedures and engine is still rough, then connect a new control unit and reinstall all panels, etc.

CO-ADJUSTMENT USING TEST DIODE 999 5280

1. Connect test diode. Connect test diode green/white wire to test point at right wheel house (connector w/pink wire). Test diode red wire should be connected to battery (+). Connect test meters, Tachometer analyser/stroboscope. Warm-up and run engine at 1500 rpm. Check the idle speed. NOTE: Warm up engine until radiator thermostat opens and then for a further 10 minutes. Ground blue-white wire to close air control valve. Switch off A/C as applicable. Adjust engine speed w/idle adjustment scre to 700 rpm. Disconnect ground from test point. Engine should increase to 750 +/- 20 rpm. If values are incorrect, check/adjust throttle controls. See THROTTLE VALVE, SWITCH, LINKAGE ADJUSTING
2. Check/adjust ignition setting. Idle speed flctuations can affect ignition setting. Make sure that fluctuations are not greater than 25 rpm. If greater, check air control valve hoses for blockages. Ignition setting should be 12°BTDC at idle. Adjust setting by turning distributor body.
3. Check CO. Test diode should flash if CO is correct. If test diode remains on = CO is too high (rich air/fuel mixture). If test diode remains off = CO is too low (lean air/fuel mixture).
4. Adjusting CO. CO should only be adjusted after all possible faults have been checked/rectified. Remove seal. Turn off engine. Drill two 2mm (0.08 in.) holes in plug. Withdraw plug w/circlip pliers. Start engine. Adjust CO content. CO screw should be turned until test diode starts to flash. Turning adjustment screw, counterclockwise reduces CO and clockwise increases CO. 15 is the adjustment range.
5. Seal CO adjustment screw. Always use a new plug. Push plug into position. Disconnect test instruments.

CO ADJUSTMENT USING CO METER

1. Connect tachometer- stroboscopic timing light/analyser CO-meter. Warm-up engine and run at 1500 rpm.
2. Check idle speed. NOTE: Engine should be warmed-up until radiator thermostat opens and then for a further 10 minutes. Ground red-white wire from test point to close air control valve. Switch off A/C as applicable. Adjust engine speed w/idle adjustment screw to 700 rpm. Disconnect ground from test point. Engine should increase to 750 +/- 20 rpm. If values are incorrect check/adjust throttle controls. See THROTTLE VALVE, SWITCH, LINKAGE ADJUSTING
3. Check/adjust ignition setting. Idle speed fluctuations can affect ignition setting. Make sure that fluctuations are not greater than 25 rpm. If greater, check air control valve for blockages. Ignition setting should be 12°BTDC at idle. Adjust setting by turning distributor body.
4. Disconnect Lambda sond. Check CO-content, it should be 0.4-0.8 percent.
5. Adjusting CO-content. CO should only be adjusted after all possible faults have been checked/rectified. Remove seal and turn off engine. Drill two 2mm (0.08") holes in plug. Withdraw plug w/circlip pliers. Start engine. CO should be adjusted until test diode begins to flash. Turning the adjustment screw counterclockwise reduces the CO and turning clockwise increase CO. 15 turns is the range for the adjustment screw. Always use a new seal CO adjustment screw plug. Push plug into position.
6. Connect Lambda sond. Turn off engine. Disconnect test equipment. Instal plug in exhaust pipe. WARNING: Adapter can be extremely hot.

CO-ADJUSTMENT USING VOLVO MONO TESTER

1. Connect Mono-Tester to the Batter positive and negative posts, HT wire for No. 1 cylinder, ignition setting sensor/stroboscope, CO test point (pink wire). Warm up and run the engine at 1500 rpm.
2. Check the idle speed. NOTE: Run the engine until themostat has opened and then for a further 10 minutes. Close idle control valve by grounding blue-white lead in connector on left-hand wheelhouse. Switch off A/C as applicable. Adjust engine speed w/idle adjustment screw to 700 rpm. Disconnect ground from test point. Engine speed should increase to 750 +/- 20 rpm. If values are incorrect, check/adjust throttle controls. See THROTTLE VALVE, SWITCH, LINKAGE ADJUSTING
3. Check/adjust ignition setting. Idle speed fluctuations can affect ignition setting. Make sure that fluctuations are not greater than 25 rpm. If greater, check air control valve hoses for blockages. Ignition setting should be 12°BTDC at idle. Adjust setting by turning distributor body.
4. Check CO level. Turn adjustment knob on Mono-tester to 4-cyl. At correct CO level, pointer should move between 20°-70°.
5. CO should only be adjusted after all possible faults have been checked/rectified. Remove seal. Turn off engine. Drill two 2mm (0.08") holes in plug. Withdraw plug w/circlip pliers and start engine. Adjust CO so that Mono-tester pointer moves between 20°-70°. Turning the adjustment screw counterclockwise reduces the CO and turning clockwise increase CO. 15 turns is the range for the adjustment screw. Always use a new seal CO adjustment screw plug. Push plug into position. Disconnect test instruments.

INJECTORS, QUICK CHECK

Start engine and listen to injectors. A clicking sound should be heard if valves are operating properly. Hold a screw driver against injector to amplify sound.

If No Click Is Heard

Interchanged connector w/one that operates properly. If fault is trasferred to the "known-good" injector, this shows that the fault lies w/wiring. If original injector still does not function, it is probably defective. Mearsure injector resistance. Resistance should be 16 ohms at 20°C (68°F). Resistance increases as temperature rises.

If A Click Is Heard But Engine Is Rough

Let engine run at idle. Disconnect/connect wire from injectors one at a time. If engine speed drops considerably when wire is disconnected, injector is probably in full working order.

To remove and install injectors, fuel rail & pressure rugulator do it as one unit. (Scheme 24)

Fuel Rails & Injectors. Scheme 24

Pressure Testing

Check breather hose connected between radiator and expansion tank. Fit new hose if hose is cracked. Using a T-piece, connect pressure tester to thin hose connected between radiator and expansion tank. Increase pressure and check opening pressure of expansion tank cap, and for leaks. Opening pressure is 65-85 kPa (9.2-12.0 psi). Check that pressure does not drop noticeably for 3 minutes.

Coolant

Since aluminum is used in the engine, active corrosion protection in the coolant is necessary to help prevent corrosion damage. Use genuine Volve coolant, type C (blue-green) diluted w/clean water in proportions 50/50. This mixture helps to prevent corrosion and frost damage. Never top-up the cooling system w/water alone. Use genuine Volvo coolant diluted w/clean water in proportions 50/50. The coolant should be changed regularly since the corrosion-protective additives in the coolant loose their effect in time.

Draining

Set heater control to MAX. Disconnect one lead from battery. Unscrew and remove cap from expansion tank. Remove engine splash guard. Open tap on right side of cylinder block to drain coolant. A hose can be connected to tap to prevent spillage. Disconnect hose at bottom of radiator. Close tap. Reconnect lower radiator hose. Install splash guard and reconnect battery.

Filling

The filling capacity is approximately 10 qts. (9.5L). Fill cooling system through expansion tank. Warm up engine and top-up with coolant. Refit cap on expansion tank.

THROTTLE VALVE, SWITCH, LINKAGE ADJUSTING

1. The throttle is adjusted at the factory and normally requires no further adjustment unless mechanical problems are suspected. Remove link rod from throttle pulley. Loosen throttle switch attaching screws (3mm Allen). Loosen lock nut on adjustment screw. Loosen adjustment screw until throttle is completely. Tighten adjustment screw until it contacts link rod and then tighten an additional 1/2 turn. Tighten lock nut and make sure that adjustment screw does not turn during this procedure. Adjust throttle switch.
2. Check throttle switch setting. Open throttle switch slightly and listen. A click should be heard to indicate that switch actuates. To adjust, slacken retaining screw (3mm Allen). Turn switch clockwise slightly. Turn switch back again until a click is heard. Tighten retaining screws. Recheck setting.
3. Check/adjust throttle cable. Check for smooth operation of pulley. Both cables should be taut in idle position but not affect position of throttle pulley. Pulley should contact idle stop. Adjust cables if necessary. Depress accelerator to floor and check that pulley contacts full throttle stop.
4. Connect/adjust link rod. Place 1mm (0.04") feeler gauge between throttle pulley and idle speed stop. Clearance between throttle lever and adjustment screw should be 0.1mm (0.04"). Adjust link rod if necessary.
5. Check/adjust kick-down cable (A/T). Depress accelerator to floor. NOTE: Do not operate throttle pulley by hand or setting will be incorrect. At full throttle, cable sleeve-clip seperation should be 50.4-52.6mm (1.98-2.07"). At idle, seperation should be 0.25-1.0mm (0.1-0.4").
6. Check idle speed. NOTE: Engine should be warmed-up until radiator thermostat opens and then for a further 10 minutes. Connect a tachometer. Ground blue-white wire from test point to close air control valve. NOTE: Switch off A/C
7. Adjust idle speed w/idle adjustment screw. Idle speed should be 700 RPM. Adjust idle speed if necessary. Disconnect ground wire from test point. Idle speed should increase to 750 +/- 20 RPM.

Volvo ECU Harness Connector Removal Pull outward and down to remove connector. Scheme 25

Volvo ECU Terminal Locations Always use back of terminals for test connections. Scheme 26

PRELIMINARY CHECKS

The following systems and components must be in good condition and operating properly before beginning diagnosis of the fuel injection system.

Engine Does Not Start

1. Blade Fuse Defective.
2. No Spark (ignition system).
3. Fuse No. 12, defective.
4. Connectors not connected.
5. Air intake system leakage.
6. Fuel pump, defective.
7. Line pressure, incorrect.
8. Poor grounds.
9. No current.
10. Pump/System relay, defective.
11. Starter motor wiring, defective.
12. Ignition coil wiring, defective

Engine Difficult to Start (Cold/Warm)

1. Connectors not connected.
2. Air intake system leakage.
3. Line pressure, incorrect.
4. Starter motor wiring, defective.
5. Temperature sensor, defective.
6. Starting system function defective.

Erratic Running (Poor or No Idle)

1. Air intake system leakage.
2. Injectors, defective.
3. Line pressure, incorrect.
4. Air mass meter, no current or ground
5. Air mass meter wiring, defective
6. Air mass meter, defective

Excessive fuel consumption

1. Fuel leakage.
2. Throttle valve switch incorrectly adjusted.
3. Line pressure, incorrect.
4. Throttle valve switch, defective
5. CO adjustment, incorrect.

Low top speed poor performance

1. Throttle valve switch incorrectly adjusted valve does not open completely.
2. Air intake system leakage.
3. Tank pump, defective.
4. Line pressure, incorrect.
5. Throttle valve switch, defective.
6. Full throttle function, incorrect.
7. CO adjustment, incorrect.

Erratic Idle

1. Air intake system leakage.
2. Engine does not run on all cylinders
3. Air control valve hose blocked/disconnected
4. Throttle valve, loose/incorrectly adjusted.

Excessive high idle speed

1. Temperature sensor connector, loose.
2. Throttle valve switch, adjustment.
3. Temperature sensor, defective.
4. Throttle valve switch, defective.
5. Throttle control incorrectly adjusted.
6. Idle speed, incorrectly adjusted.

Excessive low idle speed, cold engine

1. Fast idle function.
2. Temperature sensor, defective.
3. Air control valve, defective.

Poor Acceleration, Jerking

1. Acceleration enrichment, defective.

If engine does not start, check and see if the following items are defective: blade fuse, fuse no. 12, fuel pump, pump/system relay, starter motor wiring, ignition coil wiring. Test the following items: no spark (ignition system), connectors not connected, leakage of air intake system, line pressure incorrect, poor grounds, no current.

If the engine has difficulties starting, test the following items: Connectors are not connected, leakage of the air intake system, incorrect line pressure. Check and see if the following items are defective: starter motor, temperature sensor, starting system function.

Poor Or No Idle (Erratic Running)

If engine runs poorly or has no idle check the following items: Air intake system leakage, defective injectors, line pressue incorrect, air mass meter has no current or ground, defective air mass meter wiring, defective air mass meter.

If fuel consumption is noticeably high, test the following items: Fuel leakage, throttle valve switch, incorrectly adjusted, incorrect line pressure, defective throttle valve switch, incorrect CO-adjustment

Low Top Speed, Poor Engine Performance

If engine operates poorly at all speeds, test the following items: Throttle valve incorrectly adjusted, valve does not open completely, air intake system leakage, defective tank pump, incorrect line pressure, defective throttle valve switch, incorrect full throttle function, incorrect CO-adjustment

Eratic Idle

In case of eratic idle test the following: Air intake leakage , engine does not run on all cylinders, air control valve hose is either blocked or disconnected, and the throttle valve is either loose or incorrectly adjusted.

Excessively High Idle Speed

In case of highly excessive idle speed test the following: Loose temperature sensor connector, throttle valve switch adjustment, defective temperature sensor, defective throttle valve switch, throttle control incorrectly adjusted, idle speed incorrectly adjusted.

Excessively Low Idle Speed, Cold Engine

If there is excessively low idle speed while the engine is cold, then check the following: Fast idle function, defective temperature sensor or defective air control valve.

For poor acceleration or jerking then there is probably defective acceleration enrichment.

LH Jetronic Fuel Injection System Wiring Diagram. Scheme 27