Servicing / Maintenance

The D-Jetronic was regularly measured in the workshops with the “blue box” from BOSCH EFAW 228. However, if this box has a long out of service time, there are many contact problems and therefore incorrect measurements. However, individual measurements with a standard Volt-Meter or a Ohm-Meter are also possible.

It is very helpful to collect a few connectors from an imposed wiring harness as adapters with cables.

Measuring the injection system

Intake air temperature and engine temperature sensors are NTC- resistors.

NTC: Negative temperature coefficient

This means that the resistance decreases with increasing the temperature.

Check the fuel hoses and the fuel pressure in the ring line

All fuel hoses, especially those above the injection valves, tend to leak. If there is a smell of petrol after the engine has been switched off, there is a great danger of fire. Quick action is required here.

For more information about injection valves, see the chapter on Preservation of Values / Security.

Important! Short circuit the pump at the pump relay (connections 30 to 87) and then measure the pressure. It should be 2.1 +0.1 bar.

  • The pressure is increased by screwing in the screw (first loosen the lock) on top of the system pressure regulator
  • This gives the spring above the diaphragm a different, higher preload.

Never reduce the pressure below the minimum of 2.1 bar! If the mixture is too lean, the engines are susceptible to piston burners.

Better is 2.2 bar. The low additional consumption brings better internal cooling of the engine due to lower combustion temperatures.

Check flow rate

The return hose comes off the bottom of the system pressure regulator.Disconnect this hose at the connection to the fuel line on the body and lead it into a container, then control the pump (for this purpose short-circuit the relay from connection 30 to 87. The set flow must be at least 100 litres/hour, i.e. 1.66 litres/minute. “ONLY” the return flow may be measured.

If the flow rate is not reached, change the fuel filter. It is also possible that the voltage is too low (voltage drop with long line or oxidation) or a defect in the fuel pump.

Trigger contacts in the ignition distributor ("bit")

Carefully remove the rubber protection and the plug on the ignition distributor.

Remove the pulse trigger from the ignition distributor by loosing the 2 screws and visually check the contacts.

If the two pairs of contacts have a grey coating, they can be carefully cleaned with a glass eraser.

Because the current at these contacts is very low, the smallest oxidation and oily smearing can cause malfunctions. (dropouts in driving operation)

The wear of the contacts is kept low if the cams in the ignition distributor are lubricated with a little hot position grease. VOLVO has recommended relubrication every 5000 kilometers.

Bent and heavily worn contacts must be replaced. (Re-bending is not recommended)

The bit can now be reinstalled in the ignition distributor. Carefully attach the plug and rubber protection cap.

Afterwards it is recommended to check the ignition and to adjust it if necessary. If necessary, replace the breaker, adjust the dwell angle and set the ignition timing.

The ignition is one of the main causes of problems or malfunctions and not the injection system itself. In case of doubt, replace the circuit breaker, capacitor, distributor cover, wiring harness and spark plugs.

Resistance mesurements

The sensor is located at the front after the air filter

  • Set at +20°C = 400-500 Ohm

  • Colder: higher resistance

  • Warmer: lower resistance

The engine temperature sensor is located on the right side of the cylinder head. (Closed to the auxiliary valve)

  • Resistance at plus 20°C: 2000-3000 Ohm
  • Resistance at plus 40°C: 1000-1400 Ohm
  • Resistance at plus 80°C: 180-200 Ohm

if the old black version of the temperature sensor is still installed, generally replace it with the new brown version

Resistance injectors

  • 2,4 Ohm at plus 20°C per injector

Note: Do not apply any voltage at the injectors. They can get off.

Check Pressure Sensor

Disconnect the connector and measure the resistance of the primary winding between pin 7 and pin 15.

Setpoint: approx. 90 Ohm

Measure the resistance of the secondary winding between pin 8 and pin 10.

Setpoint: approx. 350 Ohm

Important!
Use a vacuum pump to suck out the pressure sensor. It must hold the vacuum for approxymatly 3 minutes, then it’s sealed. Alternative Test-Methode: Use a vacuum hand pump to suck out the pressure sensor. Only if it can hold the vacuum between -0.5 and -0.45 bar >10 sec. is it leakproof. If it leaks, the pressure sensor must be replaced. A repair of the defective barometer box is very complex and accordingly expensive. When repairing/replacing the barometer box, make sure that the exact Bosch part number is indicated. B20E and B20F engines are different and have different intake characteristics.  If there is a leak, the control unit greases up immediately, and this is equal to the control value for the full load signal, the engine speed goes up at idle.

Pay attention to the hose to the intake manifold, it must be absolutely tight. In case of incorrect air, the measured values of the pressure sensor are no longer correct and the mixture is greased (see section above). Also note the exact mounting method, because on some chassisi-No. the pressure sensors were mounted 180° turned and the length of the hose to the manifold was shorter.

Possibilities for malfunction:
Injection nozzles sealing rings leaking (especially the one under the nozzle holder). All rubber sealing rings must be replaced. Pay attention to the small diameter of the injection valve at the tip (8 or 9.4 mm diameter possible). For further information see also under Preservation of Values / Security.

Intake manifold gasket leaking, burnt through or cracked.

Brake booster or leaking no-return valve.