Ok

8. j Starts the diesel injector test. High pressure fuel pipe

Fuel injector

Fig. 7.34 Using the piezoelectric pick-up and the Bosch PMS 100 to examine diesel injection details

Fuel injector

Fig. 7.34 Using the piezoelectric pick-up and the Bosch PMS 100 to examine diesel injection details

3,44 ms INJECTION PULSE

877 ftPM

3,44 ms INJECTION PULSE

877 ftPM

1 The injection pumps plunger moves in the supply direction thus generating a high pressure in the pressure gallery.

2 The delivery valve opens and a pressure wave proceeds toward the injector.

3 When the injector opening pressure is reached, the needle valve overcomes its needle spring force and lifts.

4 The injection process ends, the delivery valve closes and the pressure in the line drops. This quick drop causes the nozzle to close instantly, preventing the nozzle from opening again, and preventing backflow of combustion gases.

1 The injection pumps plunger moves in the supply direction thus generating a high pressure in the pressure gallery.

2 The delivery valve opens and a pressure wave proceeds toward the injector.

3 When the injector opening pressure is reached, the needle valve overcomes its needle spring force and lifts.

4 The injection process ends, the delivery valve closes and the pressure in the line drops. This quick drop causes the nozzle to close instantly, preventing the nozzle from opening again, and preventing backflow of combustion gases.

Fig. 7.35 Diesel injection pressure pattern at idle speed 7.8.1 TESTING THE INJECTION POINT ADVANCE

When other facilities on the PMS 100 scope are brought into use it is possible to obtain a trace of the TDC sensor signal and the pressure signal simultaneously. The set-up is shown in Fig. 7.36.

If the engine is now run at idle speed, the advance period can be observed, as shown by the two vertical lines on the trace shown in Fig. 7.37(a). When the speed is increased to 1700 rpm the effect on the advance period is seen in Fig. 7.37(b). The main benefit of this test is it enables one to check the injection point in relation to TDC and this gives an indication that the timing control on the pump is functioning correctly.

7.9 Sensor tests on other systems

The survey of computer controlled systems that is the subject of Chapter 1 shows that the systems rely on sensor inputs for the live data that permits the systems to operate. The diagnostic techniques that are described in the above sections are equally applicable to virtually any computer controlled system on a vehicle. The following examples show other tests that can be applied as part of a diagnostic procedure.

The piezo pickup is clamped on the fuel line of the first cylinder, close to the injector and connected via the blue filter probe to INPUTA.(See figure below).The TDCsensorsignal isconnected to INPUT B

Do not use the ground lead of Channel B, since the instrument is already grounded through the pickup adapter to the fuel line.

• MultiScope key sequence

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