Porsche 944 - Manual (Page 163)

944 S/944 S2 Fuel System - Electronic Control
24/28
Test Point 24: Alternator, Regulator
Misfiring of the engine could be caused by
the peak voltage of the alternator.
Take drive belt off of the alternator. Start the
engine.
Check alternator and regulator if the
disturbances have been eliminated.
Test Point 25: Leads K and L
Connections for diagnosing between the
DME control unit and fasters are made with
both leads K and L Check the folIowing
points when diagnosing is not possible.
1. Power flow test (see wiring diagram)
Lead L: Pin 7 (19-pin diagnostics socket) -
Pin 13 (DME plug)
Lead K: Pin 8 (19-pin diagnostics socket) -
Pin 55 (DME plug)
2. Ground short test (see wiring diagram)
Lead L: Voltage on Pin 7 (19-pin diagnostics
socket) must be > 8 V with the ignition
turned on.
Lead K: Voltage on pin 8 (19-pin diagnostics
socket) must be > 8 V with the ignition
turned on.
Possible Causes of Fault:
- Ground short or break in wiring or plug
connections.
- Faulty control unit, which is connected on
these leads (could be any diagnosable
control unit; does not always have to be
the DME control unit).
Checking: Pull off plugs on diagnosable
control units one after the other until there
is
> 8 V. Replace fault-eausing control unit.
- Tester faulty.
- Power supply lacking on diagnostics
socket.
- Ground supply lacking on diagnostics
socket.
Information for idle speed and idle speed
CO test:
a) Idle speed
944 S engines have adaptive idle speed
volumetric efficiency regulation since 1987
modeIs. This means that the idle speed of all
versions does not have to be adjusted. The
system of cars with adaptive idle speed
volumetric efficiency regulation should be
adapted each time the DME control unit had
been disconnected on permanent positive or
after each inspection.
Idle speed control value for engine at
operating temperature:
840 +- 40 rpm
b) Idle speed CO of cars without catalytic
converter
CO level is still adjusted on the CO adjusting
screw in the air flow sensor.
Requirements:
- Engine at operating temperature.
- Engine and ignition in perfect running
condition.
- All electric consumers switched off.
- CO tester at operating temperature,
calibrated and adjusted correctly.
DME - Diagnosing/Troubleshooting
Printed In Germany - XXI, 1989
D 24/28 - 29