Ignition System Diagnosis Chart - Jeep 1987 Wrangler Workshop Manual

I
ELECTRICAL
IGNITION SYSTEM - RENIX
(4-Cyl.
Engine)
IGNITION SYSTEM DIAGNOSIS CHART
CONDITION POTENTIAL C A U S E REPAIR
Weak spark or no
spark at plugs (engine
will not start).
1. Loose or damaged coil rotor,
distributor cap, ignition wires, or
spark plugs.
1. Refer to secondary circuit
diagnosis. Replace as
necessary.
2. Loose or dirty + or - wire
connections at coil terminals.
2. Clean terminals and wire
connectors. Be sure wire
connectors are properly seated
on coil terminals and are not
wedged between coil body
and terminal.
3. Loose connectors at ICM
or E C U .
3. Verify that wire connectors are
firmly plugged into ICM and/or
E C U .
4. Loose or corroded battery
ICM or E C U ground wire
connections.
4. Clean and retighten ground
connections. (NOTE: All three
are grounded at the engine oil
dipstick bracket.)
5. Battery weak or discharged. 5. Recharge battery. Replace
battery if charging does not
restore battery specific gravity
to minimum of 1.235 or if battery
fails heavy load test.
6. Low voltage across terminals A
and B of the ICM connector 1.
6. Check the voltage between
terminals A and B using
voltmeter.
- With ignition On and starter
engaged (engine cranking),
voltage should be minimum of
9.5 volts. If the voltage is OK,
go to next step. If the voltage is
low, check continuity of ICM
and E C U ground wires. Repair
or replace as necessary.
7. Malfunction in the ignition coil
primary or secondary windings
or coil is damaged (cracked or
severely dented). (NOTE: Volt
ohmmeter must have a
minimum of 1 megohm
impedance.)
7. Check primary and secondary
resistance with ohmmeter.
The primary resistance should
be 0.4 to 0.8 ohms maximum.
Secondary resistance should be
2500 to 4000 ohms maximum.
Replace coil if damaged or
faulty. Proceed to next step if
coil is OK.
8. Check E C U and ICM with
MS 1700 tester.
8. Replace ICM or E C U if either
fails the MS 1700 test
sequence.
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