Car repair can be risky, and it’s crucial to proceed with caution. This guide uses a flowchart approach to help diagnose common car starting problems related to the starter, spark, and fuel systems.
Starter System Diagnosis
Does the starter crank and turn over the engine when you turn the key?
If no, consider these possibilities:
- Neutral Safety Switch Issues: For automatic transmissions, ensure the car is in Park or Neutral. A faulty neutral safety switch might prevent power from reaching the starter. In manual transmissions, check the clutch pedal switch.
- Key Lock Problems: If you can’t turn the key or remove it, it might be stuck in gear, preventing the starter from engaging.
Does the starter spin at high speed or make a clashing or grinding sound without turning the engine?
If yes, the issue might be with the starter motor or flywheel:
- Starter Solenoid Failure: The solenoid engages a gear to mesh with the flywheel. If it fails, the starter may spin without turning the engine. Corroded terminals or a stuck plunger can also cause this.
- Flywheel or Pinion Gear Damage: Missing or damaged teeth on the flywheel or starter pinion gear can prevent proper engagement, often accompanied by a grinding sound. Try manually turning the engine slightly using a socket wrench on the crankshaft pulley to engage different teeth. Safety First: Ensure the ignition is off and remove the wrench before attempting to start the car.
Does the battery read above 12 Volts?
Use a digital voltmeter for accurate readings.
- Low Battery Voltage: A healthy battery should read around 12.8V when the car is off. If it drops below 12V when headlights are turned on, it’s likely undercharged.
- Jump Start Test: If jump-starting or pop-starting (manual transmission) works, the problem is likely the battery or charging system.
- Battery Condition: Check battery water levels (if not sealed) and consider a specific gravity test if the battery isn’t holding a charge. Batteries have a limited lifespan, typically rated in months on the casing.
- Charging System Check: With the engine running (in Park or Neutral, parking brake engaged), battery voltage should be above 14V, indicating charging. If not, suspect alternator or voltage regulator issues. The voltage regulator is often easier and cheaper to test. Remember the alternator needs power from the regulator to generate electricity. Common alternator failures include rectifier diode problems.
Have you cleaned the battery terminals and connections?
- Corroded or Loose Terminals: Check for oxidation or loose connections at the battery terminals. This is a common cause of starting problems, especially if you only hear clicking from the starter relay or slow cranking.
- Cleaning Procedure: Remove connectors, clean posts and connector interiors with sandpaper or emery cloth. Ensure connections are tight.
- Ground Connections: Check and clean the battery ground connection to the chassis and the engine-to-chassis ground strap.
Starter Relay and Safety Bypass (Use with Caution):
- Cars use a starter relay to manage high current flow to the starter. A faulty relay or blown fuse in the starter circuit can prevent power to the starter.
- Bypass for Testing (Advanced): Only for experienced individuals and with extreme caution. You can carefully bypass the starter relay or ignition switch to directly power the starter for diagnostic purposes. Crucially, ensure the car is in Park or Neutral to prevent accidental movement. This bypasses safety features like the neutral safety switch.
Starter Removal and Bench Test:
- If issues persist, remove the starter for out-of-car testing. Disconnect the battery ground cable first to prevent electrical accidents.
- Visual Inspection: Check starter terminals for corrosion.
- Bench Test: Use jumper cables to connect the starter case to ground and the main terminal to positive battery. The starter motor should spin, and the pinion gear should extend.
Spark System Diagnosis
Does the engine fire and try to catch, or does it just crank endlessly?
- No Firing: If the engine cranks without any attempt to start, suspect spark or fuel delivery issues.
- Initial Firing then Stalling: If it briefly tries to start but then stalls, it could be fuel-related (flooding or fuel starvation). Backfiring can indicate timing problems. Engine fires suggest timing and fuel leak issues – prioritize safety and have a fire extinguisher ready.
Is spark getting to the plugs?
- Spark Test: Disconnect a spark plug wire, insert a screwdriver into the plug boot’s metal connector, and hold the screwdriver shaft near a grounded engine part while someone cranks the engine. A good spark should be bright and audible. Test only one wire initially.
Is there a spark from the coil secondary?
- Coil Output Test: If no spark at plugs or weak spark, the coil might be faulty. Test coil output by holding the secondary output near ground with a screwdriver and intermittently grounding the coil’s negative terminal using a jumper wire (touch and release). This simulates current changes needed for coil operation.
Do you have a mechanical distributor?
- Distributor Identification: Mechanical distributors have a round cap with spark plug wires around the edge and a central coil wire.
- Components: Under the cap, a rotor turns with the camshaft, distributing spark. Older systems use points; newer systems use Hall effect pickups.
- Maintenance: Check and clean rotor and cap contacts for corrosion. Worn contacts can increase spark gap.
- Magnetic Pickup Failure: Hall effect pickups can fail, causing stalling or hard starting. Testing procedures are in shop manuals.
- Electronic Distributors: For electronic distributors, consult the repair manual and check for OBD II codes.
Reading 12V+ at coil primary?
- Coil Power Supply Check: With the ignition key in the “run” position, check for battery voltage at the coil’s positive primary terminal. No voltage means tracing back through the ignition circuit is needed.
- Wiring Diagrams: Obtain a wiring diagram for your car to effectively trace circuits. Modern cars have complex wiring harnesses. Diagrams simplify troubleshooting by showing circuit paths and connector locations, aiding in finding open or short circuits.
Fuel System Diagnosis
Is fuel getting to the last fuel filter in line?
- Fuel Filter Check: Cars may have multiple fuel filters. Check the last filter before the carburetor or fuel injection system.
- Fuel Flow Test: Professionals use pressure gauges. A simpler method is to remove the filter, check for fuel inside, and blow through it in the direction of fuel flow (indicated by an arrow on the filter). A clogged filter will be difficult to blow through. No fuel in the filter indicates a fuel supply problem.
- Fuel Pump Test (Caution): Redirect the fuel line into a container and crank the engine to check fuel flow. Avoid sparks or flames during this test due to fire risk.
- Vapor Lock/Tank Vacuum: Blocked fuel tank vents or vapor recovery systems can create a vacuum, hindering fuel flow. Loosen the gas cap to check for a “whoosh” sound, which might indicate vacuum and resolve the issue.
Does the vehicle have electronic fuel injection or a carburetor?
- Fuel Injection Systems: Fuel-injected cars can suffer from injector failures or blockages. Systems include multi-point injection (injectors per cylinder) and throttle body injection (single injector). Diagnose using a car-specific manual, checking computer logic and supply voltage.
- Carburetor Systems: For carburetors, use engine starter fluid sprayed into the carburetor throat while holding the throttle open. If the engine starts and runs briefly on the spray, the problem is fuel or carburetor related. Carburetors can become clogged and may require cleaning or rebuilding, though regular rebuilds are not always necessary.
Does the car start, run briefly, and then stall?
- Possible Causes: This could be spark control system issues (timing), or the engine not cranking fast enough.
- Cranking Speed: Slow cranking can be due to low battery voltage, corroded cables, or a weak starter motor. Try jump-starting; if it starts easily, the issue is likely battery or starter related.
OBD and Diagnostic Codes
Check the OBD (On-Board Diagnostics) system.
- Diagnostic Codes: Consult your owner’s manual or a repair manual for instructions on retrieving diagnostic codes. Many cars display codes by blinking the “check engine” light in patterns.
- Code Readers: Auto parts stores may offer free code reading. You can also purchase OBD code readers for more detailed diagnostics.
Does the engine fire right up but stall as soon as you release the key to the “run” position?
- Ignition Switch Failure: This strongly suggests a faulty ignition switch. However, these are expensive, so diagnose carefully with a wiring diagram before replacement.
- Hotwiring (Emergency Use Only): In emergencies, you can “hotwire” the car to bypass the ignition switch’s “run” circuit. This is for extreme situations only and can potentially cause damage. It involves directly connecting the “run” circuit to be always on.
Environmental Factors and Stalling
If the car stalls in rain or damp weather:
- Ignition System Moisture Sensitivity: Likely related to the high-voltage ignition components: coil, wires, distributor cap. Moisture makes it easier for sparks to arc.
- Inspection: Run the engine in park or neutral at night with the hood open and look for sparks arcing from ignition components. Any arcing is abnormal.
- Water Splash: Stalling after hitting puddles indicates water splashing onto the distributor or coil. Drying ignition parts might temporarily fix the issue, suggesting replacement or shielding is needed.
If the car stalls when warm:
- Idle Speed: On older cars, incorrect idle speed can cause warm stalling.
- Sensor/Computer Issues: On newer cars, it could be a failing ignition computer or sensor.
- Vacuum Leaks: Check for vacuum leaks in intake manifold or hoses, which can cause stalling and poor performance.
- Sensor Failures: Modern cars have numerous sensors (O2, MAP, etc.). Sensor failures, though potentially indicated by OBD codes, can cause poor running, hard starting, and reduced fuel economy. Decreased fuel mileage without driving habit changes is a key indicator.
If the car stalls when cold:
- Choke Issues: Check for a stuck choke, which might be allowing too much air into the intake.
- EGR Valve: The Exhaust Gas Recirculation (EGR) valve can cause cold stalling issues.
- Vacuum Leaks: Vacuum leaks are also common culprits for cold stalling, especially in older vehicles.
- Vacuum Leak Detection: Spray starter fluid near vacuum lines; engine RPM increase indicates a leak. Use caution to avoid fire, even when the engine is cold.
Example of Cold Start Computer Issue:
- Random cold starting problems in very cold weather can be due to a faulty spark control computer. In one case, warming the computer with a heating pad resolved the issue, indicating temperature sensitivity and necessitating computer replacement.
