BMW 1989-1995 525i Service Manual page 171

F UEL INJECTION-DME
130-3
NOTE -
Poor initial driveabifity may be encountered when the
battery is disconnected and reconnected. When the bat-
tery is disconnected. the DME adaptive memory is lost.
The DME system will readapt after about ten minutes of
driving.
Fault Diagnosis
The management of engine functions is controlled by a
numbe r of systems-ignition . fuel injection, and emiss ion
contro l. Because these functions are interrelated, it is difficult
to isolate general driveability problems by examining individu-
al components. For this reason . engine management and
driveability troubleshooting information can be found in 100
Engine-General. This information is organized to help iso-
late problems and suggest more specific troubleshooting
steps by taking all of the interrelated systems into consider-
ation.
NOTE-
DME systems have an On -Been: Diagnostic (OBD)
feature that detects engine management malfunctions.
When
a
problem is identified.
a
fault code
is
stored in
the engine control module (ECM) and the Check. En-
gine lamp in the instrument cluster may eiso illuminate.
Always check for fault codes
as
the first step in trouble-
shooting
a
driveability problem. See
100 Englne-Gen·
eral ,
Warnings and Cautions
For personal safety. as well as the protection of sensitive
electr onic components. the following warnings and cautions
should be adhered to when work ing on the DME system .
WARNfNG-
• The ignition system produces high voftages that
can be fatal. Avoid contact with exposed termi-
nals. Use extreme caution when working on
a
car
with the ignition switched on or the engine running.
• Do not touch or disconnect any high voltage ca -
bles from the coil, distributor. or spark plugs wll ile
the engine is running or being cranked by the
starter.
o
Disconnecting the battery wiff erase fault code(s)
stored in memory. Check for fault codes prior to
disconnecting the battery cables. If the Check
Engine light
is
illuminated. see
100 Engine-
General
for DME fault code information. If any
other sys tem faults have been detected (indicat·
ed by an iffuminated warning light), see an au -
thorized BMW dealer. Additional sys tems with
self-diagnosfic capabilities include; ABS (ANTI
LOCK). SRS (AIR BAG). EML and ASC (Trac-
tion Control),
o
Connect and disconnect the DME system wiring
and test equipment leads only when the ignition
is switched off.
WARNING-
o
Gasoline is highly ffammable and its vapors are
explosive. Do not smoke or work on
a
car near
heaters or other fire hazards when diagnos ing
and repairing fuel syste m problems , Have
a
fire
extinguisher available in case of an emergency.
o
When working on an open fuel system, wear suit-
able hand protection.
as
prolonged contact with
fuel can cause illnesses and skin disorders.
• Before making any electrical tests that require
the engine to be cranked using the starter. dis-
able the ignition system
as
described in
120 IgnI-
tion System-DME.
CAUTION -
o
Do not connect any test equipment that delivers
a
t2- volt power supply to terminal 15 (+) of the
ignition coif. The current ffow may damage the
ECM. In general, connect tesl equipment only
as
specified by BMW. this manual. or the equip-
ment maker.
• Do not a ttempt to disable the ig nition system by
removing the center coif wire or by removing the
distributor cap (where applicable). High voltage
may arc to other electrical components causing
extensive damage.
• Do not run the engine with any of the spark plug
wires disconnected. Catalytic converter damage
may result.
o
Always wait at least 40 seconds after tum ing ott
the ignition before removing the control module
connector.
If
the conn ector is removed beiote this
time. residual power in the system relay may
damage the control module.
o
Cleanliness is essential when 1V0rking on an
open fuel system. Thoroughly clean fuel line con-
nections and surrounding areas before toosen -
ing. Avoid the use of compressed air, and avoid
moving the car. Only install clean parts.
o
Fuel system cleaners and other chemical addi-
tives other than those specifically recommended
by BMW may damage the catalytic converter. the
oxygen sensor or other fuel supply components.
FUEL PRESSURE TESTS
Checking fuel pressure is a fundamental part of trouble-
shooting and diagnosing the DME system. Fuel pressure di-
rectly influences fuel delivery . An accurate fuel pressure
gauge will be needed to make the tests.
There are two sign ificant fuel pressure values : 1) system
pressure-created by the fuel pump and mainta ined by the
pressure regulat or , and 2) residual pressure-the pressure
maintained in the closed system after the engine (and fuel
pump) is shut off.
FUEL PRESSURE TESTS