Ignition System - Hard Start/Rough Running/Misfire Codes
No.: 19/01/98/NASRef: TIB 19/07/96/US
Issue: 4
Date: 07/30/99
High-tension Ignition Lead Check
AFFECTED VEHICLE RANGE:
VEHICLES EQUIPPED WITH 14 CUX OR GEMS ENGINE MANAGEMENT SYSTEMS
SITUATION:
ASSISTANCE IN IGNITION RELATED DIAGNOSTICS
The information provided in this document is intended to assist in diagnosing ignition lead faults and summarizes ignition related issues previously issued as part of Operation Pride.
RESOLUTION:
DIAGNOSE AND IF INDICATED REPLACE INDIVIDUAL FAULTY IGNITION LEADS
NOTE:
Ignition faults are only one cause of the symptoms described in this TIB. Investigation of other causes may need to be explored to determine the root cause of the customer complaint.
When you suspect an ignition lead fault is the cause of customer complaints relating to hard starting, rough running or OBD misfire faults, the procedures in this document are provided to assist diagnosis and repairs. Only ignition leads determined to be faulty are to be replaced.
PARTS INFORMATION
WARRANTY CLAIMS:
Normal warranty policy and procedures apply.
Complete wire sets replaced due to faulty individual leads will not be paid by warranty.
Claims for damaged non-defective leads will be subject to debit.
REPAIR PROCEDURE:
14CUX IGNITION SYSTEM PHYSICAL AND RESISTANCE CHECKS
CAUTION:
Always use correct procedures when removing ignitions leads to avoid damage to the lead. Testing may be required to verify lead condition.
1. Install coil primary eyelet connectors as described in TIB 19/07/96/US.
NOTE:
Surface cracks in any engine lacquer sprayed on the wires should be ignored, but any wire that is obviously damaged should be replaced.
2. Inspect secondary ignition wires visually for damage to cables or boots.
CAUTION:
Always verify that ignition cable terminals at all locations are fully engaged.
3. Ensure that the wire connectors are fully engaged with the terminals on the spark plugs, distributor and coil.
4. If any connectors are found to be loose, the wire terminal, boot and mating half connector should be cleaned with brake cleaner and inspected:
^ If serious corrosion or damage is evident, replace the wire.
^ If no serious corrosion or damage is evident, ensure the mating connections are clean and assembled.
5. Attach TestBook with Bear Engine Analyzer to the vehicle and connect for conventional ignition as follows:
^ Attach yellow lead to coil wire.
^ Plug the yellow lead into the spot where the eight lead for plug wires on Direct Ignition attach.
^ Attach the green trigger lead to the # 1 plug wire.
^ Attach the small wire with the black clip (connected to the battery leads) to the negative terminal of the ignition coil.
^ Connect the high voltage pickup and trigger pickup around ignition wires which have been cleaned for 75 mm (3 inches) in either direction of the pickup with brake cleaner.
6. Perform the secondary ignition test and verify that the results are within the following limits:
^ Average Kv 12-17KV
^ Snap KV 17-26KV
^ Burn Time 0.4-2.0
NOTE:
Other faults, such as fueling faults may give unusual readings.
7. If any of these readings are abnormal, check the following:
^ Ensure that base time is set to the Workshop Manual specification.
^ Verify condition and gap of spark plugs.
^ Inspect condition of distributor cap and rotor (cracks, dirt, carbon brush condition).
^ Check resistance of spark plug and coil wires. Resistance should be between 98 and 213 ohms per cm (3 and 6.5 K ohms per foot).
NOTE:
A high average KV, somewhere around 35 KV (see Chart 1), is an indication of an open circuit on that cylinder.
8. Check for variables that raise average KV such as:
^ High resistance plug or coil wire
^ Connector pulled off plug distributor or coil
^ Carbon brush missing or broken in distributor cap
^ Badly worn spark plug
^ Snap throttle opening
^ Lean Mixture
^ Retarded ignition timing
NOTE:
A very low average KV, around 2-3 KV (see Chart 2) indicates a possible short circuit in the plug wire or spark plug. Only the wires that are out of specification or show signs of arcing are to be replaced.
9. Check for short circuit in the plug wire or ground electrode contacting center electrode of the spark plug.
10. Check for variables that lower average KV such as:
^ Grounded or fouled plug
^ Small plug gap
^ Rich Mixture
^ Advanced timing
^ Poor Compression (burned valves for example)
11. If there is no sign of misfire, the wires should be considered serviceable.
CAUTION:
Do not spray the wires with water. In the past, this has been the recommended procedure. This diagnostic technique can, however, be misleading. Spraying water precipitates a condition called "corona discharge." Corona discharge is a low voltage spark (outside the lead) which has the same appearance as arcing, but which does not affect the firing of the cylinder. Observing a corona discharge display can lead to misdiagnosis and unnecessary replacement of high-tension leads.
12. If a misfire is evident and no high-tension lead fault is found, investigate the following causes:
^ Fueling and Injectors
^ Compression
^ Spark plugs
^ Distributor cap and rotor
^ Ignition coil
^ Crankshaft sensor
^ Exhaust leak
^ Exhaust valve sticking
^ Worn camshaft
GEMS IGNITION SYSTEM PHYSICAL AND RESISTANCE CHECKS
1. Check spark plug wires for damage or looseness.
2. Check all primary circuit wires for tightness, damage or corrosion.
3. Replace any damaged components.
4. Remove spark plugs, ensure plug gap is correct and check for fouling.
NOTE:
Check ignition wire resistance first by measuring the entire length of a companion wire set from one plug end of the wire set to the other plug end through the coil.
5. Verify that a resistance between 24-40 K ohms is obtained when measuring from plug end to plug end with the leads attached to the coil.
6. If out of specification, measure coil and wires separately.
^ Coil secondary resistance should be 13 K ohms.
^ Spark plug wire resistance should be 98 to 213 ohms per cm (3 to 6.5 K ohms per foot) measured from coil end to plug end of the wire.
7. Replace any damaged components.
BEAR ANALYZER IGNITION TEST CONNECTION FOR GEMS IGNITION SYSTEM
1. Attach TestBook with Bear Engine Analyzer to the vehicle and connect for Direct Ignition System
^ Attach the four red leads to the right plug wires (even numbers).
^ Attach the four black leads to the left plug wires (odd numbers).
^ Attach the green trigger wire to the # 1 plug wire.
2. Perform the secondary ignition test.
Acceptable ranges for secondary testing are as shown.
NOTE:
Other faults, such as fueling faults may give unusual readings.
3. If any of these readings are abnormal, check the following:
^ Verify condition and gap of spark plugs.
^ Verify resistance of spark plug and coil wires is between 3 and 6.5 K ohms per foot.
NOTE:
A high average KV, somewhere around 3.5 KV, is an indication of an open circuit on that cylinder.
4. Check for variables that raise average KV such as:
^ High resistance plug or coil wire
^ Connector pulled off plug or coil
^ Badly worn spark plug
^ Snap throttle opening
^ Lean Mixture
^ Retarded ignition timing
NOTE:
A very low average KV, around 2-3 KV indicates a possible short circuit in the plug wire or spark plug. Any wires that are out of specification must be replaced.
5. Check for short circuit in the plug wire or ground electrode contacting center electrode of the spark plug.
6. Check for variables that lower average KV such as:
^ Grounded or fouled plug
^ Small plug gap
^ Rich Mixture
^ Advanced timing
^ Poor Compression (burned valves for example)
7. If there is no sign of misfire, the wires should be considered serviceable.
CAUTION:
Do not spray the wires with water. In the past, this has been the recommended procedure. This diagnostic technique can, however, be misleading. Spraying water precipitates a condition called "corona discharge." Corona discharge is a low voltage spark (outside the lead) which has the same appearance as arcing, but which does not affect the firing of the cylinder. Observing a corona discharge display can lead to misdiagnosis and unnecessary replacement of high-tension leads.
8. If a misfire is evident and no high-tension lead fault is found, investigate the following causes:
^ Fueling and Injectors
^ Compression
^ Spark plugs
^ Ignition coil
^ Crankshaft sensor
^ Exhaust leak
^ Exhaust valve sticking
^ Worn camshaft