Test Point 9 - Throttle Switch
TEST POINT 9 - DME 944Throttle Switch
1. Idle Contact
A) Connect Bosch test leads on one fuel injector. Connect oscilloscope on test leads as specified - see testing requirements.
This image should be displayed at idle speed.
Accelerate engine to approx. 4000 rpm - the injection time section (ti) should be wider.
Return throttle to idle stop quickly. The injection time section (ti) should no longer be visible on the screen (coasting shutoff).
The idle speed image should again be visible from a speed of approx. 1200 rpm (approx. 1300 rpm at 20 °C) on.
If the oscilloscope does not display coasting shutoff, there is a defect either in the wire leading to the control unit, the control unit itself or the throttle switch.
Throttle Valve Potentiometer (V)
B) Power Supply to Throttle Valve Potentiometer
Pull off plug on throttle valve potentiometer. Connect voltmeter on term. 1 and 2 on plug end. Turn on ignition.
Display = approx. 5 V (full load).
Connect voltmeter on term. 4 and 6. Turn on ignition.
Display = approx. 5 V (idle speed).
C) Idle Speed Contact
Connect ohmmeter on term. 12 and ground of disconnected DME control unit plug.
Display: throttle valve closed = 0 - 10 ohms
throttle valve opened (approx. 10) = inf. ohms
No Display:
Make test direct on throttle valve potentiometer. Connect ohmmeter on term. 6 and 4.
Display:
Check power flow from plug to control unit.
D) Checking Control Unit
Pull off plug on throttle valve housing.
Start and run engine at idle speed.
Bridge term. 4 and 6 on disconnected plug with a piece of wire. Boost engine speed to approx. 1600 rpm. Engine begins to surge (coasting shutoff).
E) Full Load Contact
Check tap resistance.
Pull off KLR control unit plug.
Connect ohmmeter on term. 22 and 23.
Display: throttle valve closed = 320 to 670 ohms
throttle valve wide open = 2.7 to 4.7 k-ohms
This test can also be made direct on term. 2 and 3 of the throttle valve potentiometer.
Since the full load pulse is triggered by the KLR control unit with a throttle valve gap of 650, this test can only be made on a running engine. It is recommended to pull off two fuel injector plugs, to avoid racing the engine.
Connect voltmeter on test connection term. B and C.
Start and run engine at idle speed.
Display = approx. 5 V.
Floor accelerator briefly (without racing the engine).
Display = returns to 0 V.
No Display:
Check connection between B and term. 18 on the disconnected KLR plug.
Connection Okay:
Replace KLR control unit.
Checking DME Control Unit:
Check ignition timing at 2500 rpm.
Specification: 35 ± 3° before TDC.
Bridge test connection term. B and C with a piece of wire.
Check ignition timing at 2500 rpm.
Specification: 18 ± 3° before TDC.
If there is no ignition timing control, check the connection between KLR control unit plug terminal 18 and DME control unit plug terminal 3.
Connection Okay:
Replace DME control unit.