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Conditions for Checking
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Nominal Value
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Affected Terminals: 9, 48, 49,
50, 51
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-
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Possible Trouble Codes: 25, 26,
27, 28, 81, 82, 83, 84
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Engine running at idle speed
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Engine throttle valve CLOSED
(accelerator pedal in idle position)
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Vehicle stationary
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Switch off all consumers
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AC switch OFF
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Press key F8 in the system
main menu, select the desired test using the arrow keys and confirm with YES.
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Follow the instructions in the
TECH 1 display.
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Note:
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In this test mode,
TECH 1 sets the firing angle in the control unit to a fixed value
(15 °CA) and the idle speed adjuster to a fixed position. There is no
adjustment of the firing angle and idle speed adjuster. It is then possible
to switch off the injectors of the individual cylinders.
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After selecting this test, it is
possible to select a cylinder / injector using the arrow key
"UP" and then, with the arrow key "DOWN", to switch
off / deactivate the injector of each selected cylinder for 3 s.
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In addition, the YES and NO keys
can be used to display the various data list parameters. Key F9 is used
to store the data as in the snapshot mode.
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After fixing the firing angle
and the idle speed adjuster position and before deactivating an injector, the
engine runs as approx. 1300 rpm. The oxygen sensor control functions
normally.
The test should only be started
if the cooling fan is not running (otherwise the engine speed may be approx.
200 rpm lower).
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Once an injector is deactivated,
the engine speed sinks by approx. 200 rpm. If the cooling fan starts
running during the deactivation phase, this may lead to a further decrease of
the engine speed of approx. 200 rpm.
In this test phase, uncombusted
oyxgen from the deactivated cylinder gains access to the exhaust pipe.
This means that the engine runs
lean and therefore that the oxygen sensor constantly displays a voltage lower
than 400 mV (see TECH 1 data list parameters
"O2 SENSOR" and "AIR / FUEL RATIO"). The
actual oxygen sensor control, hoewever, is switched off after an injector is
deactivated; i. e. parameter "O2 INTEGRATOR" is at 128.
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The above described check should
be performed consecutively for each cylinder. They should all indicate the
same response, i. e. the engine speed should sink by about the same amount
for each cylinder. The purpose of this check is not to test the function of
the iniectors, but is intended as a check of the mechanism /
tightness / compression of each individual cylinder.
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