Fuel Injection System - Bosch LH (turbo) Volvo 760 I

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. No Spark (ignition system).
2. Fuse No. 1 or 11 defective.
3. Poor wire connection.
4. Inlet system, air leakage.
5. Fuel pump, defective.
6. Line pressure, incorrect.
7. Charge air overpressure sw. defective.
8. Wire/components defective.

Poor Cold Starting

1. Coolant temperature sensor defective (shorted).

Surge During Engine Braking

1. Bypass valve does not open.
2. Throttle sw. incorrectly adjusted.

High fuel consumption

1. Coolant temperature sensor not connected.
2. Fuel leakage.
3. Line pressure, incorrect.
4. CO - adjustment, incorrect.

Rough Running (All engine speeds)

1. Inlet system, air leakage.
2. Injectors defective, all four cylinders do not fire.
3. Line pressure, incorrect.
4. Air mass meter, defective (emergency ckt. defective)

Rough Idle

1. Inlet system, air leakage.
2. Air control valve hoses clogged/loose.
3. Air control valve seized.
4. Coolant temperature sensor not connected properly.
5. Throttle valve, loose/incorrectly adjusted.
6. Throttle switch incorrectly adjusted.
7. Ignition setting incorrect.
8. Line pressure incorrect.
9. CO - setting incorrect.

Low top speed poor performance

1. Throttle linkage incorrectly set, throttle does not open fully.
2. Ignition setting incorrect.
3. Inlet system, air leakage.
4. Tank pump, defective.
5. Line pressure, incorrect.
6. Bypass valve does not close.
7. Charge pressure incorrect.

FUSES

Check fuse no.1 for pump relay and fuse no. 11 for tank pump. (Scheme 6)

Fuse Box. Scheme 6

CONNECTORS & GROUND CONNECTIONS

Make sure that knock sensor and coolant temperature sensor connectors are not interchanged. The knock sensor wires are green and the coolant temperature sensors are gray and black. Make sure that air control valve and throttle switch connectors are not interchanged. Air control valve wires are green, yellow/red, and gray/red. Throttle switch connector wires are orange and brown.

Check the ground connections on intake manifold. Make sure the wires are properly connected and tight. (Scheme 7) Poor connections can cause a variety of fault symptoms.

Check ground connections behind LH-control unit (Scheme 8)(main fuel pump ground). Check ground connection in trunk (pre-pump ground).

Ground Connections on Intake Manifold. Scheme 7

Ground Connections behind LH-Control Unit. Scheme 8

Check Inlet System For Leakage

If air leaks from point where air mass meter is mounted on engine, air fuel mixture will be lean.

Make sure to check the inlet system between air mass meter and intake manifold. Check all hoses and connections on the intake manifold. Check the couplings and seals for intake manifold, throttle housing etc.

Throttle Switch

To check open throttle slightly and listen. A click should be heard as soon as the throttle is opened to indicate that the idle switch opens.

To adjust slacken screws (Allen key 3mm). Turn switch clockwise slightly, then turn the switch back until the click is heard. Tighten the retaining screws. Check setting.

Fuel Pump, Tank Pump Check

Remove panel above foot pedals. Pull apart the connector next to the charge air overpressure switch. Connect the ground wire to suitable grounding point. Both wires are yellow/black, check which one is ground. Turn on the ignition to start the fuel pumps. The pumps should be heard. Remove the fuel tank cap to hear tank pump.

If neither pump operates

1. Turn off the ignition. Pull out central electrical unit from the center console and remove the system relay. (Scheme 9)
2. Turn ignition on. Check for voltage at terminal 30. If there is no voltage, then check wire and fuse no. 1 between the battery and relay.
3. Connect a bridge wire across terminals 30 and 87/2. Both of the pumps should start. If they do not check the wires between the relay and the pumps.
4. Check circuit between terminals 87/1 and 85. Use an ohm meter or test buzzer.
5. Check that terminal 86/2 is grounded (separate ground wire at charge air overpressure switch.
6. Check that terminal 86/1 is grounded. If incorrect, check wiring harness to control unit.
7. Test with new relay

Central Electrical Unit. Scheme 9

Main fuel pump does not operate

1. Check wires from fuse no. 11 and pump.
2. Check fuel pump ground.

Tank pump does not operate

1. Check fuse no. 11 wires and pump.
2. Check fuel pump ground.

LINE PRESSURE, REGULATOR

Turn off ignition. Connect pressure gauge between line and distribution rail. Use hose and adapter. Plug gauge hose. Turn gauge clock to position 1 (pointing towards hose).

Measure line pressure

Turn on ignition to start fuel pumps. Charge air overpressure switch must be ground. Line pressure should be 42 psi.

Line pressure is too high

Turn off ignition. Disconnect fuel return line from pressure regulator. Blow through line. Disconnect vacuum hose from pressure regulator. Blow through line. If both hoses are free from blockages, regulator is defective and should be replaced.

Line pressure is too low.

Pinch fuel return line with hand and check pressure increases.

If pressure rises quickly, pumps and fuel lines are OK. Replace regulator and measure again. If pressure rises slowly, this indicates a blocked fuel filter, tank pump filter, or fuel line. If fuel pressure doesn't rise, fuel pump is defective.

Check pressure regulator

Connect a vacuum pump to regulator. Use vacuum pump. Pump air out of regulator and check that line pressure drops. Line pressure should drop to same extent as drop in regulator pressure. Line should be 42psi minus vacuum.

Connect pressure tester and pump to pressure regulator. Increase pressure and check line pressure.

Turn off ignition, remove pressure gauge. Hold paper below fuel line to absorb spillage when disconnecting gauge.

Disconnect ground and reconnect pressure switch plugs. (Scheme 10)

Reconnected Pressure Switch Plugs. Scheme 10

Charge air overpressure switch

Connect pressure tester and pressure gauge. Connect equipment to hose at intake manifold.

Check charge air overpressure switch. Connect a buzzer to switch. Increase pressure w/pump. Switch should cut-out at 12.1-13.5 psi). Remove pump and pressure gauge. Reconnect hose to intake manifold.

COMPONENTS/WIRING

Turn off ignition. Remove panel beneath right side of dashboard and panel in front of right side of door. Disconnect from control unit.

Lift catch upwards and fold connector downwards. Remove the plastic cover and cover plates above terminal.

Note. Do not insert instrument probe into front of connector. Experience has shown that this can cause 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.

Check ground connections

Connect ohmmeter between ground and terminals 5, 11 & 25. Resistance should be nearly 0 in all cases. Ground wires are connected to intake manifold.

Check Lambda-sond shielding wires

Check that wires are connected to terminal 5.

Check that test point is not grounded

Connect ohm meter between ground and terminals 12 & 22. Resistance should be infinite in both cases.

Check engine speed signal from ignition system control unit

Connect tachometer between ground and terminal 1. Operate starter motor. Tachometer should show engine speed.

Check voltage supply

Turn on ignition. Connect voltmeter between ground and terminal 18. Meter should show battery voltage. Check voltage when operating starter motor. Turn off ignition.

MAIN RELAY

Connect voltmeter between ground and terminal 9. Ground terminal 21. Relay should make circuit and meter should show battery voltage.

PUMP RELAY

Ground terminal 21 to complete main relay circuit. Ground terminal 17. Pump relay should activate fuel pumps and pumps should start operating.

Connect voltmeter between ground and terminal 18 in 20-pole connector, next to right "A" pillar. Meter should show battery voltage. Disconnect ground leads.

Separate connector at right "A" pillar. It is black retainer containing three connectors: 20-pole, 11-pole, 8-pole.

INJECTORS & BALLAST RESISTORS

Connect ohmmeter between terminal 13 on control unit & terminal 18 of 20-pole connector. Resistance should be approx. 2 ohms. If this incorrect, measure resistance at injectors and a ballast resistors to find out where fault lies. Disconnect connectors when measuring. Injector resistance should be approx. 2 ohms. Ballast resistance should be approx. 6 ohms.

AIR CONTROL VALVE

Connect ohmmeter between terminal 18 of 20-pole connector and terminal 23 and 10 on control unit. Resistance should be approx. 20 ohms in both cases.

Check preheating resistor in Lamda-sond

Connect ohmmeter between ground and terminal 18 of 20-pole connector. Resistance of cold Lambda sond (20°C, 68°F) is 3 ohms. Resistance of warm Lambda sond (above 350°C, 662°F) is 13 ohms. Install 20-pole connector at right "A" pillar.

COOLANT TEMPERATURE SENSOR

Connect ohmmeter between ground and terminal 2. Resistance is temperature dependent.

COOLANT TEMP. SENSOR TEMPERATURE (1)

Check Throttle Switch

Connect ohmmeter between ground an terminal 3. Resistance should be 0. Depress accelerator pedal slightly. Resistance should increase to infinity. Throttle switch ground wire is connected to intake manifold.

Check Transmission Switch

Note. On 1985 MTX automatic gearboxes, check that wire is not grounded.

Connect ohmmeter between ground and terminal 15. With gear lever in 1st or 2nd resistance should be 0 (switch closed). With gear lever in 3rd or 4th gear resistance should be infinite. Switch is grounded via gearbox.

MASS AIRFLOW METER

1. Remove rubber sleeve from mass airflow meter to uncover wire connector. Connect voltmeter leads between ground and airflow meter connector terminal No. 5.
2. Voltmeter should read battery voltage. Connect voltmeter between terminal No. 5 and terminal No. 1. Voltmeter should again read battery voltage.
3. Connect ohmmeter leads to airflow meter connector terminal No. 2 and terminal No. 3. Ohmmeter should read approximately 3.7 ohms.
4. Connect ohmmeter between terminal No. 2 and terminal No. 6. Ohmmeter should read 0-1000 ohms.

CO-Adjustment Screw

Turn on ignition. Connect a voltmeter between terminal 14 at the LH control ground. Meter should be 0 to 2.6 volts depending on CO screw position. 0 volts is max. lean position. 2.6 volts is a max. rich position. Turn screw on air mass meter and check if voltage changes. If no voltage or no variation when screw is turned, check wiring continuity.

Note. Adjustment screw must be resealed after adjustment.

Air Mass Meter Output

Turn on ignition. Connect a voltmeter between terminal 7 at the LH-control unit and ground. Meter should show approximately 1.2 volts. Start engine. Warm engine to operating temperature (A/C off). Check output at idle, 750 rpm. Meter should show approx. 2.2 volts. Increase idle speed to 3500 rpm. Output should increase to approx. 2.9 volts. Check wiring continuity if out of specification.

Burn Off Function

Engine running at operating temperature. Connect voltmeter between terminal 4 and ground. Increase engine speed to 2500 rpm. Close throttle and let engine slow down to idle speed. Turn off the ignition. After approx. 4 seconds, the meter should deflect for 1 second. If no reading, check wiring continuity. Reinstall rubber cover.

Check signal from A/C control panel. Connect voltmeter between ground and terminal 16. Start engine. Move control to A/C ON position. Voltmeter should show battery voltage and idle speed should increase to 900 rpm. Turn off ignition.

Assemble Connector

Note. Ignition must be off when disconnecting/connecting connector.

Connect connector to control unit. Start engine. If engine does not start, test with a new control unit. Connect CO meter. Connect meter to adaptor next to catalytic cleaner.

Warm up engine.

LAMBDA-SOND

Disassemble Lambda-sond connector. Ground wire leading to control unit. CO should increase to show that wire and control unit are OK. Connect voltmeter to Lambda-sond. Meter should deflect to show that Lambda-sond functions. If CO is as specified, voltage be approx. 0.5V. Connect Lambda-sond connector.

Check/adjust CO content

Test circuit with a new control unit. If no faults are found during fault tracing procedures and engine is rough, connect a new control unit. Ignition setting, idle, CO, valve clearance, etc. should all be according to specifications.

DESCRIPTION

Throttle valve and throttle switch must be correctly set before adjusting ignition setting, idle speed, CO content.

Use open-type exhaust gas extractors. Use an exhaust gas extractor that fits loosely over the exhaust pipe.

If very powerful exhaust gas extraction is used there is risk that oil will be drawn into the exhaust system past the turbocharger gaskets. This would cause the sound damping material in the exhaust system to be soaked in oil, and cause the blue exhaust smoke for a long time. Such a condition could be misinterpreted as a inner oil leakage and could be the cause of unnecessary repairs.

Three types of test equipment can be used to check/adjust CO content: 1) CO-Meter, which should be only used in special cases during fault tracing procedures, and 2) Test diode 999 5280.

CO METER

1. Connect the test equipment, which consists of a tachometer, stroboscope and CO meter. Connect the CO meter to adapter next to the catalyst. Use gauge connector, valve facing exhaust pipe.
2. Warm up the engine to 1500 rpm.
3. Check the idle speed. NOTE: The A/C should be switched off. Check that the engine speed is within 750 +/- 20 rpm. Adjust with the idle speed screw if necessary.
4. Check/adjust the ignition setting. NOTE: The idle speed fluctuations can affect the ignition setting. Make sure that fluctuations are not greater that +/-20 rpm. If greater, check the air control valve function. Ignition setting is °12 (+/- 2°) BTDC at idle. Adjust setting by turning distributor body.
5. Disconnect the Lambda-sond. Check the CO content. The conditions should be checked/adjusted within 5-10 minutes of radiator thermostat opening. The CO content is 0.4-0.8%.
6. Adjust CO as applicable. It should only be adjusted after all possible faults have been checked. Remove the seal. Turn off engine. Drill two 2mm (0.08 in.) holes in plug. Withdraw plug with circlip pliers. Start engine.
7. Adjust CO content. The CO content setting is 0.6%. Turn adjustment screw counter-clockwise, reduces CO. Turn adjustment screw clockwise, increases CO. The adjustment range for the screw is 15 stepless turns. Connect Lambda-Sond.
8. Check basic setting of idle. The engine should be warmed-up until the radiator thermostat opens and then for a further 10 minutes. Ground the red-white wire from test point to close air control valve. Adjust engine speed with idle adjustment screw to 700-750 rpm. Disconnect ground. Engine speed should increase to 750 +/- 20 rpm . Turn off the engine. Disconnect the test equipment. Install the plug in exhaust pipe. WARNING: The adapter can be very hot.
9. Seal CO adjustment screw (as applicable). Use a new plug. Tap plug into position.

CO-CHECKING USING TEST DIODE 999 5280-6

1. Connect test diode, green/white wire, to the point at the right wheel house (connector with green/white wire). The test diode, red wire, should be connected to battery (+) terminal.
2. Connect test meters: tachometer, analyzer. Warm up the engine at 1500 rpm.
3. Check/adjust ignition setting. NOTE: The idle speed fluctuations can affect the ignition setting. Make sure that the engine speed is 750 +/- 20 rpm. If greater, then check the air control valve hoses for blockages. The ignition setting is 12°(+/-2°) BTDC at idle. Adjust setting by turning distributor body.
4. Check CO. If correct the test diode should flash. The CO is too high (rich air/fuel mixture) if the test diode remains on. If it remains off then the CO is too low (lean air/fuel mixture)
5. Adjust CO. It should only be adjusted after all possible faults have been checked. Remove the seal. Turn off engine. Drill two 2mm (0.08 in.) holes in plug. Withdraw plug with circlip pliers. Start engine.
6. Adjust CO content. The CO screw should be turned until test diode starts to flash. Turn adjustment screw counter-clockwise, reduces CO. Turn adjustment screw clockwise, increases CO. The adjustment range is turns.
7. Seal CO adjustment screw (as applicalbe). Use a new plug. Tap plug into position.

INJECTORS, QUICK CHECK

1. Start engine and listen to injectors. A clicking sound should be heard if valves are operating properly. Hold a screwdriver against the injector to amplify the sound.
2. If no click is heard, then interchange connector with that of an injector that operates properly. If the fault moves to other injector this shows that the fault lies with wiring or ballast resistor. If injector still does not function, it is probably defective. Measure injector resistance, which should be 2 ohms (varies w/temperature).
3. If a click is heard but the engine is rough, then let the engine run at idle. Ground the test point for air valve. Disconnect/connect wire from injectors one at a time. If engine speed drops considerably when wire is disconnect, then injector is probably in full working order.

REMOVAL & INSTALLATION

Remove and install fuel injection and injectors as one unit.

IDLE SPEED CHECK

Note. Engine should be warmed up until radiator thermostat open and then for a further 10 minutes.

1. Switch off A/C as applicable. Adjust engine speed with idle adjustment screw to 650 rpm. Disconnect ground from test connector. Engine speed should increase momentarily in excess of 1000 rpm, and then stabilize at 750 +/- 20 rpm.
2. If the engine speed does not increase when removing ground from test connector, check the following: Installation of air valve. Arrow on air valve should point toward intake manifold. Voltage supply to air valve. Air valve control circuit. System with new air valve.

IDLE SPEED ADJUST

Ground tests connector. Using idle speed adjustment screw, adjust idle speed to 700-750 rpm. Disconnect ground from test connector.

Bosch LH Jetronic Schematic. Scheme 11

Component Location and Identification. Scheme 12