GMC T Series 1994 Repair Manual page 613

N O T IC E : W h e n f a s t e n e r s a r e r e m o v e d , a lw a y s r e in s t a l l th e m a t th e s a m e lo c a t io n f r o m w h ic h th e y w e r e
r e m o v e d . I f a f a s t e n e r n e e d s to b e r e p la c e d , u s e t h e c o r r e c t p a r t n u m b e r f a s t e n e r f o r t h a t a p p lic a t io n . I f
th e c o r r e c t p a r t n u m b e r f a s t e n e r is n o t a v a ila b le , a fa s t e n e r o f e q u a l s iz e a n d s t r e n g t h ( o r s t r o n g e r ) m a y
b e u s e d . F a s t e n e r s t h a t a r e n o t r e u s e d , a n d t h o s e r e q u ir in g t h r e a d lo c k in g c o m p o u n d w ill b e c a lle d o u t.
T h e c o r r e c t t o r q u e v a lu e m u s t b e u s e d w h e n in s t a llin g fa s t e n e r s t h a t r e q u ir e it. I f t h e a b o v e c o n d it io n s
a r e n o t f o llo w e d , p a r t s o r s y s t e m d a m a g e c o u ld re s u lt.
SUBJECT
General D escription......................................................................................................................................................6D4A-1
Delco Remy Distributors......................................................................................................................................... 6D4A-1
Ignition C o il............................................................................................................................................................. 6D4A-1
Ignition Control Module....................................................................................................................................... 6D4A-1
Pole Piece and Coil Assem bly.......................................................................................................................... 6D4A-1
Disassem bly.................................................................................................................................................................... 6D4A-3
D istributor.................................................................................................................................................................... 6D4A-3
Inspection and Electrical Tests.................................................................................................................................6D4A-4
A ssem bly..........................................................................................................................................................................6D4A-5
D istributor.................................................................................................................................................................... 6D4A-5
Special T o o ls ..................................................................................................................................................................6D4A-6
DELCO REMY DISTRIBUTORS
Distributors with separate coils and sealed connectors
are used on light duty truck engines (figure 1). The
ignition coil connects to the distributor cap through a
high tension wire.
The distributor uses an internal magnetic pickup
assembly that consists of a permanent magnet, pole
piece with internal teeth, and pickup coil. When the
rotating teeth of the timer core line up with the teeth of
the pole piece, voltage is induced in the pickup coil.
This voltage signals the ignition control module (ICM) to
trigger the primary ignition circuit. Current flow in the
primary circuit is interrupted and up to 35,000 volts is
induced in the ignition coil secondary winding. This volt­
age is directed through the secondary ignition circuit to
fire the spark plugs.
IGNITION COIL
The coil is built like a transformer with the winding
surrounded by a laminated iron frame. It generates a
high secondary voltage (up to 35,000 volts) when the
primary circuit is broken. It connects to the distributor
by a high tension wire.
SECTION 6D4A
DISTRIBUTORS
CONTENTS
GENERAL DESCRIPTION
IGNITION CONTROL MODULE
The ignition control module (ICM) is a solid state unit
containing many circuits. These circuits control spark
triggering, switching, current limiting, dwell control, and
distributor pickup. The vehicle's computer sends signals
to the module to control dwell and spark timing. The
module may have seven or eight terminals, depending
on the ignition system.
POLE PIECE AND COIL ASSEMBLY
The pole piece and plate assembly (often referred to
as the pickup coil assembly) consists of a stationary
pole piece with internal teeth and a pickup coil and
magnet that are located between the pole piece and a
bottom plate (figures 2 and 3).
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