Ignition module failure
Ignition module failure is a common ignition-related problem on the Pontiac Fiero, especially on V6 cars with distributor ignition.
A failing ignition module can cause a no-start condition, stalling, misfiring, intermittent shutdown, loss of spark, poor performance, or a hot engine that will not restart until it cools down.
Overview
The ignition module is part of the ignition system.
On 2.8L V6 Fieros, the ignition module is mounted in the distributor and works with the distributor pickup coil, ignition coil, ECM, Electronic Spark Timing circuit, wiring, and related connectors.
Some four-cylinder Fieros use distributor ignition, while later four-cylinder Fieros use a distributorless ignition system. On distributorless systems, the ignition module is part of a different ignition arrangement involving crankshaft sensing and coil packs.
Because ignition-system layout depends on model year and engine, diagnosis should be based on the actual system installed in the car.
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Location
Image wanted: Photo or diagram showing the 2.8L V6 distributor ignition module location under the distributor cap, including the pickup coil leads and module connectors.
On V6 Fieros, the ignition module is located inside the distributor.
The distributor is mounted on the engine and also contains the pickup coil. The ignition module connects to the pickup coil, ignition coil, ECM-related circuits, tachometer signal circuit, and distributor wiring.
On distributorless four-cylinder systems, the ignition module is not in a distributor. It is part of the DIS ignition assembly and should be diagnosed using the correct information for that system.
Function
The ignition module helps control ignition spark.
On distributor ignition systems, the ignition module receives a signal from the distributor pickup coil and controls ignition-coil triggering. It also provides reference information used by the ECM.
At low engine speed and during cranking, the module plays a direct role in spark control. Once the engine is running above the bypass threshold, the ECM can take over spark timing control through the Electronic Spark Timing system.
If the module, pickup coil, ignition coil, wiring, or ECM-related ignition circuits fail, the result may be no spark, poor spark control, Code 42, or a crank/no-start condition.
Electronic Spark Timing relationship
The Fiero ignition system uses Electronic Spark Timing, often abbreviated as EST.
On distributor ignition systems, the ignition module and ECM communicate through circuits that include:
- Reference signal
- Reference ground
- Bypass circuit
- EST circuit
- Ignition power
- Tachometer signal
The ignition module provides a reference signal that allows the ECM to determine engine speed and timing information.
The bypass circuit is used to switch from module-controlled timing to ECM-controlled timing once engine speed is high enough. If the bypass or EST circuit is open, shorted, grounded, or not switching correctly, Code 42 may be set.
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V6 distributor ignition
On the 2.8L V6, the ignition module is part of the distributor ignition system.
Related parts include:
- Distributor
- Pickup coil
- Ignition module
- Ignition coil
- Distributor cap
- Rotor
- Spark plug wires
- Spark plugs
- ECM
- EST and bypass wiring
- Tachometer signal circuit
Because many of these parts can cause similar symptoms, the ignition module should not be diagnosed by symptoms alone.
Four-cylinder ignition systems
Four-cylinder Fiero ignition systems vary by year.
Some four-cylinder Fieros use distributor ignition.
Later four-cylinder Fieros use a distributorless ignition system with an ignition module, crankshaft sensor, and coil packs rather than a conventional distributor.
Because the hardware and diagnosis are different, the term “ignition module” should be interpreted according to the engine and ignition system installed in the car.
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Heat-related failure
Ignition modules can fail from heat, age, poor electrical connections, poor heat transfer, poor mounting-surface contact, or low-quality replacement parts.
A common owner-reported pattern is that the engine starts and runs when cold, then stalls or will not restart when hot. After the module cools down, the engine may restart.
Heat-related failure is common enough that many Fiero owners keep a spare ignition module and the tools needed to replace it.
Heat-sink compound
When replacing a distributor-mounted ignition module, proper heat-sink compound should be used between the module and the distributor mounting surface.
Ordinary dielectric grease is not the same as heat-sink compound. Dielectric grease is useful for protecting some electrical connections, but it should not be used as a substitute for thermal compound under the ignition module.
The module mounting surface should be clean so heat can transfer properly from the module into the distributor base.
Symptoms
Common symptoms of ignition module or related ignition-system problems include:
- Engine cranks but does not start
- Engine starts cold but stalls when hot
- Engine shuts off suddenly while driving
- Engine restarts after cooling down
- No spark
- Weak or intermittent spark
- Misfire
- Tachometer does not move while cranking
- Tachometer drops suddenly when the engine stalls
- Poor performance
- Reduced fuel economy
- Stored Code 42 in some cases
- Intermittent no-start with no obvious fuel problem
These symptoms can also be caused by other ignition, fuel, ECM, wiring, or power-supply faults.
Tachometer clue
On distributor ignition systems, tachometer behavior can be a useful clue.
If the engine is cranking but the tachometer does not move, the ignition module, pickup coil, distributor wiring, ignition power feed, reference circuit, or related connector should be checked.
A tachometer signal does not prove the ignition system is fully working, but a missing tach signal during cranking can help narrow the diagnosis.
Code 42 relationship
Code 42 is related to the Electronic Spark Timing circuit.
A Code 42 does not automatically mean the ignition module itself has failed. Possible causes include:
- Faulty ignition module
- Poor ignition-module connection
- Open or grounded bypass circuit
- Open or grounded EST circuit
- Poor distributor connector contact
- Wiring fault between ignition module and ECM
- ECM connector problem
- ECM problem
- PROM not fully seated, where applicable
Because Code 42 can involve both the ignition module and wiring/ECM-related circuits, the diagnostic chart for Code 42 should be followed rather than replacing parts at random.
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Related components
Ignition module diagnosis should also include nearby and related parts:
- Ignition coil
- Distributor
- Pickup coil
- Spark plugs
- Spark plug wires
- Ignition timing
- ECM
- Ground problems
- Wiring harness
- Battery
- Fuses and relays
No-start diagnosis
Ignition module failure is one possible cause of a crank/no-start condition.
A practical no-start diagnosis should determine whether the engine has:
- Spark
- Injector pulse
- Fuel pressure
- ECM power and reference signal
- Correct ignition power feed
- Usable pickup coil or crank signal, depending on system
On the 2.8L V6, factory no-start diagnosis includes checking for RPM indication during cranking, checking spark with a spark tester, checking injector pulse, and checking the ignition/reference circuit before condemning the ignition module.
Related topics:
- No-start diagnosis
- Code 42
- Pickup coil
- Ignition coil
- Distributor
- ALDL diagnostics
- Fuel pressure test
Diagnosis
A practical diagnostic order is:
- Determine which ignition system the car has.
- Determine whether the engine has spark.
- Watch the tachometer while cranking.
- Check whether ECM data or diagnostic equipment shows RPM while cranking, if available.
- Inspect ignition module connectors.
- Inspect the distributor pickup coil and wiring, if equipped.
- Check ignition power and ground.
- Check the ignition coil.
- Read Diagnostic trouble codes.
- Diagnose Code 42 if present.
- Test or substitute the ignition module if appropriate.
- Inspect related wiring and ECM connections.
- Confirm that fuel pressure and injector pulse are not the real cause of the no-start.
Do not assume the ignition module is bad until power, ground, pickup/crank signal, coil, connectors, and related wiring have been considered.
Pickup coil relationship
On distributor ignition systems, the pickup coil provides the signal the ignition module uses to trigger spark and provide reference information.
A failing pickup coil or damaged pickup-coil wiring can produce symptoms similar to ignition module failure.
Possible pickup-coil-related symptoms include:
- No spark
- Intermittent spark
- Stall when hot
- No tachometer movement while cranking
- Intermittent no-start
- Misfire or poor running
The pickup coil and its small wires should be inspected carefully when replacing or testing the ignition module.
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Ignition coil relationship
A bad ignition coil can also cause no spark, weak spark, intermittent spark, misfire, hard starting, or hot restart problems.
Before blaming the ignition module, check the ignition coil, coil connector, high-voltage coil wire, distributor cap, rotor, and spark plug wires.
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Connector and wiring problems
Ignition module problems are often discussed as part failures, but connector and wiring problems can create the same symptoms.
Common issues include:
- Loose distributor connectors
- Corroded terminals
- Broken pickup-coil wires
- Heat-damaged wiring
- Poor ignition-coil connector contact
- Poor ECM connector contact
- Poor ground
- Previous wiring repairs or modifications
- Harness damage near the distributor or exhaust heat
Intermittent ignition problems should include a careful connector and wiring inspection.
Replacement
When replacing a distributor-mounted ignition module:
- Disconnect the battery if appropriate.
- Remove the distributor cap as needed.
- Note connector locations before disassembly.
- Disconnect the module connectors carefully.
- Remove the old module.
- Clean the mounting surface.
- Apply proper heat-sink compound.
- Install the replacement module.
- Reconnect wiring.
- Reinstall the distributor cap.
- Verify spark and engine operation.
- Check ignition timing if the distributor or timing-related parts were disturbed.
Use the correct module for the engine and ignition system.
Roadside spare
Many Fiero owners carry a spare ignition module because sudden failure can leave the car stranded.
Useful roadside items may include:
- Spare ignition module
- Correct tool for module screws
- Small amount of proper heat-sink compound
- Basic hand tools
- Spare ignition coil, if desired
- Contact cleaner, if desired
A spare module is useful only if the actual problem is the module. Pickup coil failure, ignition-coil failure, bad wiring, loss of ignition power, or fuel-system problems can produce similar symptoms.
Service notes
When working on the ignition module:
- Use the correct module for the engine and ignition system.
- Use proper heat-sink compound under distributor-mounted modules.
- Do not substitute ordinary dielectric grease for heat-sink compound.
- Inspect connectors before replacing parts.
- Inspect pickup-coil wiring on distributor systems.
- Check ignition power and ground.
- Check for Code 42 if the engine runs poorly or the Service Engine Soon light is on.
- Do not assume the ECM is bad before checking module, wiring, and connector faults.
- Do not assume every hot no-start is caused by the ignition module.
Notes
Ignition module failure should not be diagnosed by symptoms alone.
Pickup coil failure, ignition coil failure, bad connectors, poor grounds, wiring faults, ECM issues, fuel-pressure problems, injector-pulse problems, and other ignition faults can produce similar symptoms.
Many Fiero owners keep a spare ignition module and the tools needed to replace it because sudden ignition module failure can leave the car stranded.