Ignition System - Weak/No Spark
86ford24Article No. 86-2-20
IGNITION SYSTEM - TFI - WEAK OR NO SPARK - DIAGNOSTIC TIP
FORD 1982-86 ESCORT, EXP; 1983-86 THUNDERBIRD, LTD, CROWN VICTORIA, MUSTANG; 1984-86 TEMPO; 1986 TAURUS
LINCOLN-MERCURY 1982-83 LN7; 1982-86 LYNX; 1983-86 COUGAR, MERCURY, GRAND MARQUIS, CONTINENTAL, MARK VII, LINCOLN; 1984-86 TOPAZ; 1986 SABLE
LIGHT TRUCK 1983-86 EAND F-SERIES, RANGER, BRONCO; 1984-86 BRONCO II; 1986 AEROSTAR
CALIBRATIONS: All with TFI Systems
If the TFI module fails and causes a short to ground, the primary winding of the ignition coil can be damaged. The TFI diagnostic procedure published in the Shop Manual will not identify this condition.
When servicing a weak or no spark condition, perform the following:
1. Check for spark using the procedures found in the Manual Information, Computerized Engine, Quick Test Section, Test 1.
2. If there is no spark, test the coil primary resistance using Rotunda digital volt-ohmmeter 007-00001, as shown.
3. If the coil primary resistance is O.K., continue with the diagnostic procedure in Test 1.
4. If the coil primary resistance is not O.K., replace the coil and recheck for weak or no spark. If the spark is now O.K., the problem is resolved.
5. If the spark is still NOT O.K., continue with normal diagnostic procedure in Test 1.
OTHER APPLICABLE ARTICLES: None
WARRANTY STATUS: "INFORMATION ONLY"
Wiring Harness
TFI-IV
Part 2
Test 5
TEST EQUIPMENT: VOM, STRAIGHT PIN
TEST PROCEDURE
1. Separate wiring harness connector from ignition module. Inspect for dirt, corrosion, and damage.
NOTE: PUSH connector tabs to separate.
2. Disconnect wire at S terminal of starter relay.
3. Attach negative (-) VOM, Rotunda Number 007-00001, lead to distributor base.
4. Measure battery voltage.
5. Following table below, measure connector terminal voltage by attaching VOM to small straight pin inserted into connector terminal and turning ignition switch to position shown.
CAUTION: Do not allow straight pin to contact electrical ground.
CONNECTOR IGNITION SWITCH
TERMINAL WIRE/CIRCUIT TEST POSITION
#2 TO IGNITION RUN
COIL (-) TERMINAL
#3 RUN CIRCUIT RUN AND START
#4 START CIRCUIT START
6. Turn ignition switch to Off position.
7. Remove straight pin.
8. Reconnect wire to S terminal of starter relay.
TEST RESULT TEST RESOLUTION
90 percent of ^ Test result OK.
battery ^ Go to Part 2, Test 6.
voltage minimum
Less than 90 ^ Inspect for faults in wiring
percent of harness and connectors.
battery ^ Refer to vehicle wiring
voltage diagram for appropriate
circuit.
^ Damaged or worn ignition switch, Refer to Shop Manual, Group 33.
Primary Circuit Continuity
TFI-IV
Part 2
Test 8
TEST EQUIPMENT: VOM, STRAIGHT PIN
TEST PROCEDURE
1. Separate wiring harness connector from ignition module. Inspect for dirt, corrosion, and damage.
NOTE: PUSH connector tabs to separate.
2. Attach negative (-) VOM, Rotunda Number 007-00001, lead to distributor base.
3. Measure battery voltage.
4. Attach VOM to small straight pin inserted into connector terminal No. 2.
CAUTION: Do not allow straight pin to contact electrical ground.
5. Turn ignition switch to Run position and measure terminal No. 2 voltage.
6. Turn ignition switch to Off position.
7. Remove straight pin.
TEST RESULT TEST RESOLUTION
90 percent of ^ Go to Part 2, Test 5.
battery voltage minimum
Less than 90 ^ Go to Part 2, Test 9.
percent of battery voltage
Ignition Coil Primary Resistance
TFI-IV
Part 2
Test 3
TEST EQUIPMENT: VOM
TEST PROCEDURE
1. Turn ignition switch to Off.
2. Disconnect ignition coil connector. Inspect for dirt, corrosion, and damage.
3. Measure resistance from positive (+) to negative (-) terminal of ignition coil, using Rotunda digital volt-ohmmeter 007-00001.
TEST RESULT TEST RESOLUTION
0.3 to 1.0 ^ Test result OK.
ohm ^ Go to Test 4.
Less than ^ Replace ignition coil.
0.3 ohm or greater than 1.0 ohm