Some tips to keep in mind :
• Always position the piezo pickup on the fuel line at about the same distance from the injector.
• Place the pickup on a straight part of the fuel line. Don’t place it on a bent part of the line.
• Always compare results with a reference waveform from a good diesel engine to get acquainted with the signal
shape.
• Always compare signals at the same engine speed (RPM).
• Pump timing is critical and should occur within 1 degree of crankshaft rotation.
Diesel Injector
(Diesel RPM Measurement and Diesel Injection Pattern Display)
Use the optional Diesel Probe Set consisting of a Piezo Pickup, which is clamped on the diesel fuel pipe, and a
Diesel Adaptor to be connected to the CH A input of the instrument.
• Reference Waveform
DUR = Duration of the injection pulse
• Analysis of Injection Pattern at Idle Speed
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6.6 DIESEL TESTS
The diesel test functions are selected if “IGNITION: DIESEL” has been set in the VEHICLE DATA menu. To choose
a preset DIESEL test menu, select COMPONENT TESTS from the MAIN MENU. From the resulting menu, select
DIESEL TESTS menu.
Introduction
During the compression stroke of a diesel engine, the intake air is compressed to about 735 psi (50 Bar). The
temperature hereby increases up to 1,292 ° to 1,652 °F (700 ° to 900 °C). This temperature is sufficient to cause
automatic ignition of the Diesel fuel which is injected into the cylinder, shortly before the end of the compression
stroke and very near to the TDC (Top Dead Center).
Diesel fuel is delivered to the individual cylinders at a pressure of between 5145 psi and 17,640 psi (350 Bar and
1200 Bar). The start of the injection cycle should be timed within 1 ° Crankshaft to achieve the optimum trade-off
between engine fuel consumption and combustion noise (knock). A timing device controls the start of the injection
and will also compensate for the propagation times in the fuel delivery lines.
Diesel RPM measurements are necessary for adjusting idle speed, checking maximum RPM, and performing smoke
tests at fixed RPM values.
Measurement Conditions
Cleaning : The fuel lines (to be measured on) should be cleaned in order to assure a good contact of the fuel line
itself to the Piezo Pickup and ground clip. Use sandpaper (preferably a de-greaser) to clean the lines.
Positioni ng and Pr obe Connection : The Piezo Adapter should be placed as close as possible to the Diesel
injector on a straight part of the fuel line. Clamp the ground clip close to the Piezo Pickup. Make sure that the ground
clip does not make contact to the piezo itself or to adjacent fuel lines. Connect the adapter to the instrument. Notice
that the ground wire is shorter than the signal wire in order to have the weight of probe and cable loaded on the
ground wire, not on the signal wire. The piezo element may not bounce or rattle on the fuel line, or make contact to
other fuel lines or any other material close by.
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RPM = 903
DUR = 0.6 ms
VEHICLE DATA
IGNITION
DIESEL
DIESEL
COMPONENT TESTS
DIESEL TEST MENU
DIESEL INJECTOR
ADVANCE
MENU ( )
MENU ( )
The delivery valve opens
and a pressure wave
proceeds toward the
injector.
When the injector opening
pressure is reached to more than
1,470 psi (100 Bar), the needle
valve overcomes its needle spring
force and lifts.
The injection pumps plunger
moves in the supply direction
and thus generating a high
pressure in the pressure
gallery.
The injection process ends, the
delivery valve closes and the
pressure in the fuel line drops.
This quick drop causes the
nozzle to close instantly,
preventing the nozzle from
opening again, and preventing
backflow of combustion gases.
