BMW 5251 Service Manual page 359

Ignition System
-
Turn ignition on and check for battery voltage,
If battery voltage is not present, checlt wire between termi-
nal 15 and the unloader relay. See ELE Electrical Wiring
Diagrams.
-
Turn ignition off.
Remove coil and inspect coil housing for hairline cracks or
leaking casting material. Replace any cracked or leaking coil.
NOTE-
A leaky coil may indicate a faulty Engine Control Module
(ECM). Check ECM before installing a new coil.
CAUTION-
Note location of coilground straps before coil removal; rein-
stall in the same location.
Use a multimeter to test:
Coil primary resistance at coil terminals.
Sparlt plug connector resistance.
* Compare results to specification in Table c. lgnition coil
resistance.
Table c. Ignition coil resistance
Coil secondary
resistance
Spark plug connector:
Bosch
1
.O
I( ohm
t
20%
1.8
ir ohm
t
20%
Component
Co~l prlmary
resistance
-
Replace ignition coil or sparlt plug connector if resistance
readings do not meet specifications.
4
Remove ignition coil to be tested.
Install BMW special tool 12 7 030 (A) on coil to be tested.
Connect ground jumper between coil mounting point
(B)
and engine ground point (C).
Clip scope high pick-up lead (D) around ignition lead.
Start engine.
Compare scope pattern with diagrams in Oscilloscope di-
agnostic diagrams.
NOTE-
When replacing ignition coils, ensure that the replacements
Terminal
1 (-)
and
15 (+)
are from the same manufacturer with the same partlcode
numbers. I f individual coils with the correct specifications are
not available. all coils should be re~laced.
Resistance
0.8
ohms