Volvo Coupes/Sedans/Wagons 1970-1989 Repair Guide

Bosch Electronic Fuel Injection

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1975 AND EARLIER MODELS



See Figures 1 and 2

All 1973 and earlier fuel injected models and the 1974-75 164 use the Bosch electronic fuel injection system. Fuel is drawn from the fuel tank by the electric fuel pump and forced through the fuel lines and filter to the pressure regulator. The pressure regulator supplies fuel at a constant pressure of 28 psi (193 kPa) to the injectors. The electromagnetic fuel injectors are mounted in the intake ports of the cylinder head.

The duration of fuel injection, and, consequently, fuel quantity, is controlled by engine rpm and load. Engine rpm information is supplied to the electronic brain via the distributor triggering contacts. Engine load information is supplied by the intake air pressure sensor. The electronic brain uses this information to determine the length of time the injectors will remain open. During warm-up periods, the cold start valve injects extra fuel into the intake air stream when the starter is operated. At the same time, the auxiliary air regulator supplies extra air until the engine reaches operating temperature.

When the engine is accelerated, the throttle valve switch sends electrical impulses to the brain to increase the time the injectors are open. When decelerating, the throttle valve switch sends another impulse to the brain, closing off the fuel flow. When engine speed drops to approximately 1,000 rpm, the fuel supply is turned on again, allowing a smooth transition to idle speed.



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Fig. Fig. 1: Schematic for the electronic fuel injection system-B20F engine



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Fig. Fig. 2: Schematic for the electronic fuel injection system-B30F engine

COMPONENT TESTING, ADJUSTMENT & REPLACEMENT



Through 1975, B20 and B30 engines

The fuel injection system is repaired simply by replacing the defective component. There are adjustments that can be made to the pressure regulator, throttle valve, throttle valve switch, throttle stop-screw, and the fuel mixture. To make resistance checks, use an ohmmeter and for continuity checks, a 12V test light. If the control unit is defective, return it to a qualified repair agency and install a new unit.

CONTROL UNIT

See Figure 3

The idle mixture may be adjusted with the slotted knob on the control unit. This operation is best performed with the use of a CO meter, which is available on the dealer level. The control unit may be tested only with the help of sophisticated test equipment available, again, only at the dealer level. To replace the control unit:

  1. On 1800 series models and 1975 164 models, disconnect the defroster hose, remove the control unit bracket retaining screws, and lower the unit to the floor. On 140 series and 1973-74 164 models, move the passenger's front seat all the way back, unscrew the bolt securing the seat front, move the seat forward while folding the seat bottom to the rear, remove the control unit retaining screws, and draw out the unit.
  2.  
  3. Remove the screw for the cap holding the cable harness to the unit. Pull out the plastic cover strip.
  4.  



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Fig. Fig. 3: Acquire or fabricate the puller shown to facilitate removal of the control unit plug contact

  1. Construct a puller out of 5 / 64 in. (2mm) welding wire (see illustration) to disconnect the main plug contact. Insert the puller in the rear of the control unit and pull out the plug carefully.
  2.  

To install:
  1. Press the plug contact firmly into the new or reconditioned control unit. Fit the plastic cover strip, retaining cap, and screw.
  2.  
  3. Fit the control unit into place and install its retaining screws. Install the remaining components in the reverse order of removal. Have the mixture adjusted, if necessary.
  4.  

PRESSURE REGULATOR

The regulator may be adjusted with its adjusting nut. Pinch and disconnect the flexible fuel hose between the pressure regulator and the header pipe and insert a tee fitting and pressure gauge. Tighten the fuel connections and start the engine. Loosen the locknut and adjust the pressure to 28 psi (193 kPa). If the regulator cannot be adjusted properly, it must be replaced. Remove the tee fitting and gauge, and connect the fuel hoses. Replace the regulator as follows:

  1. Place pinch clamps on the three fuel hoses connected to the regulator.
  2.  
  3. Loosen the hose clamps and remove the hoses.
  4.  
  5. On 1970-71 models, remove the regulator from its bracket and replace it with a new one.
  6.  
  7. Connect the fuel hoses to the new regulator, tighten the hose clamps, and remove the pinch clamps.
  8.  
  9. Start the engine and check for fuel leaks.
  10.  

FUEL INJECTORS

See Figure 4

The fuel injectors may be checked for electrical function and sealing only. To check for electrical function, remove the electrical connection and connect an ohmmeter across the injector terminals. Resistance should be 2.40 ohms at 68°F (20°C).

Do NOT apply 12V current to the injectors. Such voltage would immediately destroy the injector. The internal electric components work on a maximum of three volts.



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Fig. Fig. 4: Cutaway view of the fuel injector

After following Steps 1 and 3-5 below, simply observe the amount of fuel which leaks from the injector with the fuel hose still connected. Acceptable leakage is 5 drops per minute or about one drop every 12 seconds. Excessive dripping delivers too much fuel; the engine runs too rich. Symptoms similar to flooding a carbureted engine may appear. Remove and replace the injectors.

  1. On 164 models, remove the air cleaner.
  2.  
  3. Pinch shut the fuel hose to the header pipe.
  4.  
  5. Loosen the hose clamps for the injectors and lift up the header pipe.
  6.  

  1. Remove the plug contacts from the injectors. Disconnect the cable harness from the distributing pipe.
  2.  
  3. Turn the lockrings on the injectors counterclockwise so that they loosen from their bayonet fittings. Lift out the injectors.
  4.  

To install:
  1. Place the new injectors, with new washers and new rubber sealing rings, in position and secure them by turning the lockrings clockwise.
  2.  
  3. Connect the cable harness at the distributing pipe. Connect the plug contacts to the injectors.
  4.  
  5. Place the header pipe in position, and tighten the hose clamps. Remove the pinch clamps.
  6.  
  7. On 164 models, install the air cleaner.
  8.  

COLD START VALVE

The cold start valve, mounted on the intake manifold, provides the engine with extr fuel during cold start up. The injection time is governed by the thermal timer which measures coolant temperature and activates the cold start valve electrically. The cold start valve is energized when the temperature of the coolant is below 95°F (35°C). When engaged, the system provides extra fuel for up to 12 seconds, as long as the starter is engaged. To replace the cold start valve:

  1. On 164 models, remove the air cleaner.
  2.  
  3. Pinch shut the fuel line to the valve.
  4.  
  5. Remove the plug contact and the fuel hose from the valve.
  6.  
  7. Remove the two retaining screws and the cold start valve from the inlet duct.
  8.  

To install:
  1. Place the new cold start valve in position with packing and install the retaining screws.
  2.  
  3. Connect the plug contact and fuel hose to the valve. Remove the pinch clamp.
  4.  
  5. On 164 models, install the air cleaner.
  6.  

THERMAL TIMER

The thermal timer is a temperature controlled switch controlling current to the cold start valve. In addition to sensing the temperature of the coolant, an internal circuit heats up when the starter is engaged. After a certain temperature is reached, the control circuit to the cold start valve is disconnected. This prevents delivering excessive amounts of fuel to an engine being cranked for long periods. To replace:

  1. Drain the cooling system.
  2.  
  3. Disconnect the plug contacts and unscrew the thermal timer from the cylinder head.
  4.  
  5. Install a new timer and connect the plug contacts.
  6.  
  7. Refill the cooling system.
  8.  

THROTTLE VALVE SWITCH

The throttle valve switch may be adjusted with an ohmmeter. Connect the ohmmeter to the control unit (contacts 14 and 17 for 4-cylinder, and contacts 9 and 14 for 6-cylinder). Loosen the screws slightly so that the switch may be rotated. Scribe a mark at the upper switch screw on the inlet duct if one is not there already.

Close the throttle valve by turning the switch clockwise as far as it will go. Then, observing the ohmmeter, carefully turn the switch counterclockwise until the ohmmeter registers 0. At this point, the switch is turned a further 1° counterclockwise ( 1 / 2 graduation mark at upper screw), and both switch screws are tightened. Check to make sure that the ohmmeter reading rises to infinity when the throttle valve opens approximately 1°. If it becomes necessary to replace the switch:

  1. Disconnect the plug contact from the switch. Remove the two retaining screws and pull the switch straight out of the inlet duct.
  2.  
  3. Fit the new switch to the inlet duct and install the retaining screws. Connect the plug contact.
  4.  
  5. Adjust the switch.
  6.  

AUXILIARY AIR REGULATOR

The auxiliary air regulator is found at the front of the cylinder head and has a capillary tube extending into the cooling system. Its functional range is from -13°F to +140°F (-25°C to +60°C). Depending on the temperature of the coolant, the unit allows additional air into the intake manifold. As the engine heats up, the capillary tube expands and presses back the regulator slide; at 140°F (60°C), the system is completely closed and no additional air is admitted to the system.

To check the operation of the auxiliary air regulator, start the engine and allow it to reach operating temperature, 176°F (80°C). Make a note of the idle speed and then disconnect the hose between the inlet duct and the regulator. While covering the hose opening with your hand, check to see that the idle speed does not drop significantly under the first reading. A drop in idle speed indicates a leak in the regulator, requiring its replacement. Replace the regulator as follows.

  1. Drain the cooling system.
  2.  


CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted by the ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. Remove the plug contact from the temperature sensor and disconnect the air hoses from the regulator.
  2.  
  3. Remove the two retaining bolts and draw out the regulator.
  4.  
  5. Using a new sealing ring, position the new regulator to the cylinder head and install the retaining bolts.
  6.  
  7. Connect the plug contact and the two air hoses.
  8.  
  9. Refill the cooling system.
  10.  

INTAKE AIR TEMPERATURE SENSOR

Located in front of the air cleaner, this sensor informs the control unit of changes in air temperature. At air temperatures below 86°F (30°C), the injection interval (duration) increases slightly. To test this sensor, connect an ohmmeter across the terminal pins. According to the air temperature, resistance should be: 440 ohms @ 50°F (10°C); 300 ohms @ 68°F (20°C); 210 ohms @ 86°F (30°C); 160 ohms @ 104°F (40°C). Acceptable range is plus or minus 40 ohms for each listed resistance. To replace the sensor:

  1. On 164 models, remove the right drip protection, and the air hose from the right side.
  2.  
  3. Disconnect the four-way plug contact from the sensor.
  4.  
  5. Unscrew the old sensor and install a new one, taking care not to overtighten it.
  6.  
  7. Plug in the four-way contact for the sensor.
  8.  
  9. On 164 models, install the right air hose and drip protection.
  10.  

COOLANT TEMPERATURE SENSOR

The temperature sensor is located at the front of the cylinder head and informs the control unit of changes in the coolant temperature. This sensor is also tested by checking the resistance with an ohmmeter. Ohm readings will vary with coolant temperature as follows: 3000-4200 ohms @ 50°F (10°C); 2100-3100 ohms @ 68°F (20°C); 1400-2100 ohms @ at 86°F (30°C); 1000-1400 ohms @ 104°F (40°C). Target readings are the middle of the range, but anywhere within the range is acceptable. To replace the coolant sensor:

  1. Drain a portion of the cooling system so that the coolant level in the radiator and engine is below the temperature sensor.
  2.  
  3. Disconnect the plug contact from the sensor.
  4.  
  5. Unscrew the old sensor and install a new one with a new sealing ring.
  6.  
  7. Connect the plug contact.
  8.  
  9. Top up the cooling system.
  10.  

PRESSURE SENSOR

This device interprets changes in intake air pressure and communicates with the control unit. It is from this unit that the control unit gets its sense of engine load. Generally located on the right front wheel well, the sensor contains mechanical components to read air pressure and a small transformer for sending electrical signals to the brain.

The terminals should be numbered on the transformer.

Only the transformer can be checked; there are no mechanical repairs for the sensor. Using an ohmmeter, check the resistance between terminals 7 and 15. This measurement of the primary windings should be about 90 ohms. Measure the secondary winding between terminals 8 and 10 and look for about 350 ohms. Any other combination of terminals should yield an infinite resistance, i.e. no connection. If it is necessary to replace the sensor:

  1. Disconnect the four-way contact and the air hose from the sensor.
  2.  
  3. Remove the three screws retaining the sensor to the right wheel housing.
  4.  
  5. Transfer the attaching bracket to the new pressure sensor.
  6.  
  7. Position the new sensor to the wheel well and install the retaining screws.
  8.  
  9. Connect the plug contact and the air hose to the sensor.
  10.  

TRIGGERING CONTACTS

These two contacts are actuated by the distributor camshaft. The electrical message they send to the control unit is used with the air pressure data to determine when injection should begin and how long the injection should last. To inspect or replace the contact unit:

  1. Remove the distributor. (See Engine & Engine Overhaul .)
  2.  
  3. Remove the two screws securing the triggering contacts holder to the distributor and then pull out the holder.
  4.  
  5. Lubricate the fiber pieces of the contact breaker lever on the new holder with silicone cam lobe grease.
  6.  
  7. Check to see that the rubber ring is not damaged. Replace if necessary.
  8.  
  9. Install the new holder in the distributor and tighten the retaining screws.
  10.  
  11. Install the distributor.
  12.  

 
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