Mercury MerCruiser MCM 454 Mag MPI Service Manual page 730

SERVICE MANUAL NUMBER 23
Code 42 (3 of 3): Ignition Control (IC) Circuit (Scan)
Index
90-861326--1 MARCH 1999
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1. Ignition OFF.
2. Disconnect ECM connectors.
3. Ignition ON.
4. Use a DVOM with selector in the OHMS
4
range.
5. Probe ECM harness connector CKT 423
with DVOMto ground.
It should read more than 3000 Ohms.
Does it?
Probe ECM harness connector CKT 424 with a
test light to battery positive (B+).
5
Is test light on?
Open CKT 423, faulty connection or faulty igni-
6
tion module.
With Ohmmeter connected to ECM harness
CKT 423 and ground, probe harness CKT 424
with test light connected to battery positive
(B+).
7 7
As test light contacts CKT 424, resistance
should change from over 3000 Ohms to under
1000 Ohms.
Does it?
Disconnect distributor 4-way connector. Con-
nect ohmmeter between CKT 423 and ground.
8 8
Resistance should have gone high (open
circuit), does it?
Reconnect ECM and idle engine for 1 minute
9
or until code 42 sets.
CKT 424 open, faulty connections or faulty
10
ignition module.
11 CKT 423 shorted to ground.
12 Faulty ECM.
Code 42 is intermittent refer to "Diagnostic
13
Aids."
14 Disconnect ignition module 4-way connector.
Is test light on?
15 CKT 424 shorted to ground.
16 Faulty ignition module.
TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI
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Step 5 Step 6
Step 14 Step 7
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Step 9 Step 8
Step 10 Step 11
Step 12 Step 13
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Step 15 Step 16
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