No-start diagnosis
No-start diagnosis is an overview of diagnostic steps for a Pontiac Fiero that cranks but does not start, or does not crank at all.
No-start problems can be caused by battery, starter, ignition, fuel, air, compression, ECM, wiring, sensor, or security-related faults. Diagnosis should begin by identifying whether the engine cranks normally.
Overview
A no-start condition should first be divided into two basic types:
- No crank - the starter does not turn the engine.
- Crank, no start - the starter turns the engine, but the engine does not run.
These two conditions have different likely causes and should be diagnosed differently.
No crank
A no-crank condition may be caused by battery problems, bad connections, starter failure, neutral safety switch or clutch switch problems, ignition switch problems, wiring faults, or ground problems.
Related topics:
- Battery
- Starter
- Starter problems
- Battery cables
- Ground problems
- Ignition switch
- Neutral safety switch
- Clutch safety switch
Crank, no start
A crank/no-start condition usually requires checking for ignition spark, fuel pressure, injector operation, ECM power, sensor signals, and mechanical condition.
Basic checks include:
- Does the engine have spark?
- Does the fuel pump run briefly when the key is turned on?
- Is there correct fuel pressure?
- Are the injectors firing?
- Are any Diagnostic trouble codes stored?
- Does the engine have compression?
- Are the distributor, timing, and ignition components functioning correctly?
Ignition checks
Ignition problems are a common cause of crank/no-start conditions.
Related topics:
- Ignition module failure
- Ignition coil
- Distributor
- Pickup coil
- Spark plug replacement
- Ignition timing
- Code 42
Fuel checks
Fuel delivery problems can also cause crank/no-start conditions.
Related topics:
- Fuel pump problems
- Fuel pressure test
- Fuel pump relay
- Oil pressure switch
- Fuel filter replacement
- Fuel injectors
- Fuel pressure regulator
ECM and electrical checks
The ECM and related wiring must receive proper power and ground for the engine to run.
Related topics:
- ECM
- ALDL diagnostics
- Diagnostic trouble codes
- Ground problems
- Fuses and relays
- Wiring diagrams
- Connector pinouts
Mechanical checks
If spark and fuel are present, mechanical condition should be checked.
Related topics:
Diagnostic order
A practical diagnostic order is:
- Verify battery voltage and cable condition.
- Determine whether the engine cranks.
- Check for spark.
- Check fuel pump operation.
- Check fuel pressure.
- Check injector operation.
- Read diagnostic trouble codes.
- Inspect grounds, fuses, connectors, and wiring.
- Check compression and mechanical timing if needed.
Notes
Avoid replacing parts at random. A no-start condition should be diagnosed by testing one system at a time.
On Fieros, ignition module failure, pickup coil failure, fuel pump problems, bad grounds, poor connections, and wiring issues are common causes of no-start complaints.