Disabling Ignition System; Checking For Spark - BMW 5251 Service Manual

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ignition
System
Disabling ignition system
The ignition system operates in a lethal voltage range and
should be disabled any time engine service or repair work is
being done that requires the ignition to be switched on.
The engine management system can be disabled by remov-
ing the DME main relay. The relay is located in the electronics
box (E-box) in the left rear of the engine compartment, be.
neath the interior microfilter housing.
CAUTION-
Relay locations may vary. Use care when identifying relays.
See 610 Electrical Component Locations.
Checking for spark
CAUTION-
If
a
spark test is done incorrecth damage to the Engine Con-
trol Module (ECM) or the ignition coils may result.
NOTE-
Spark plug replacement is covered in 020 Maintenance.
Check~ng for spark is d~fflcult on englnes wlth d~str~butorless
ignition systems.
Try removing the spark plugs and inspecting for differences
between them. A poor-firing plug may be wet with fuel and/or
~.
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black and sooty, but not always. If a coil is not operating, the
engine management system will electrically disable the fuel
injector to that cylinder. The key is to look for differences be-
tween cylinders.
Ignition coil assembly, testing and
replacing
C4 UTION-
Use a digital multimeter for the following tests.
I
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Remove plastic engine cover from top of valve cover by pry-
ing off bolt covers and removing cover mounting bolts.
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Raise car slowly while constantly checking position of jack
and car.
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Disconnect harness connector from coil. Connect multimeter
between terminal 15 (+) in connector and ground.
4
Terminal identification are typically molded into connector. In
photo, terminals are from left to right: 1, 4a, 15.