Est Ignition System Check; Test Description - MerCruiser GM4 Service Manual

(+)
PUR
IGNITION
COIL
CONNECTOR
TO
DISTRIBUTOR
CAP
IGN COIL
S
E
C

Test Description

Numbers below refer to circled numbers on the
diagnostic chart.
1. Two wires are checked, to ensure that an open is
not present in a spark plug wire.
a. If spark occurs with EST connector discon-
nected, pick-up coil output is too low for EST
operation.
2. A spark indicates the problem must be the distrib-
utor cap or rotor.
3. Normally, there should be battery voltage at the
"C" and "+" terminals. Low voltage would indicate
an open or a high resistance circuit from the dis-
tributor to the coil or ignition switch. If "C" terminal
voltage was low, but "+" terminal voltage is 10
volts or more, circuit from "C" terminal to ignition
coil or ignition coil primary winding is open.
4. Checks for a shorted module or grounded circuit
from the ignition coil to the module. The distributor
module should be turned "OFF," so normal volt-
age should be about 12 volts. If the module is
turned "ON," the voltage would be low, but above
1 volt. This could cause the ignition coil to fail from
excessive heat. With an open ignition coil primary
winding, a small amount of voltage will leak
through the module from the "BAT" to the "TACH"
terminal.
Index
1C- 10 - TROUBLESHOOTING
("C")
GRY
DISTRIBUTOR
HEI MODULE
+ C
+ C
B
FILTER
PNK
B
P
BLK
R
CONN
I
BRN
A
GRY
A

EST Ignition System Check

PICK-UP
COIL
PN
BRE
BRE
WHT
WHT
5. Applying a voltage (1.5 to 8 volts) to module termi-
nal "P" should turn the module "ON" and the "tach"
terminal voltage should drop to about 7-9 volts.
This test will determine whether the module or coil
is faulty or if the pick-up coil is not generating the
proper signal to turn the module "ON." This test
can be performed by using a DC battery with a rat-
ing of 1.5 to 8 volts. The use of the test light is
mainly to allow the "P" terminal to be probed more
easily. Some digital multi-meters can also be
used to trigger the module by selecting ohms,
usually the diode position. In this position the me-
ter may have a voltage across its terminals which
can be used to trigger the module. The voltage in
the ohm's position can be checked by using a se-
cond meter or by checking the manufacturer's
specification of the tool being used.
6. This should turn "OFF" the module and cause a
spark. If no spark occurs, the fault is most likely in
the ignition coil because most module problems
would have been found before this point in the
procedure. A module tester could determine
which is at fault.
B R E
DISTRIBUTOR 3 TERMINAL
CONNECTOR
71572
90-816462 2-695