Owner's Problem Description
The owner reports that their 1989 Ford Probe has no spark despite performing several actions. They confirmed that the relays are functioning as they click when the ignition is activated. A new ignition coil was installed, but there is still no spark. The ignition module was removed and tested good, with clean connections and no noticeable changes in engine cranking speed. The owner was advised that the distributor might be faulty and inquired about possible tests to confirm this. They also heard about a fuel shut-off safety switch but noted that the vehicle has never been in an accident. The car has been sitting a lot and is not garage-kept.
Professional Technical Analysis
This 1989 Ford Probe, equipped with a turbocharged 4-cylinder engine, has a history of intermittent starting issues leading to no spark condition. The vehicle has been sitting for extended periods, potentially contributing to electrical connection degradation. The ignition system comprises several components, including the ignition coil and the ignition module, which have been inspected and tested good. The TFI (Thick Film Ignition) module, which is critical for proper ignition timing, is mounted on the distributor and could be a point of failure despite testing well. Voltage checks reveal that the coil's positive terminal has power, indicating that the supply is intact, but the negative terminal remains static, suggesting that the coil is not being pulsed to create a spark. The distributor could also be malfunctioning, affecting rotor and cap functionality. Given the age of the vehicle, corrosion, and wear could lead to poor connectivity within the ignition circuit. Additionally, the potential for a malfunctioning fuel shut-off safety switch should be considered, although it’s less likely given the vehicle's history. Overall, the vehicle requires a thorough diagnostic approach focusing on the ignition system, including the TFI module's operational integrity, the distributor's mechanical condition, and verifying all electrical connections.
Possible Causes
Most common causes (ordered by frequency):
- Faulty TFI Module: The TFI module, critical for ignition timing, is known to fail intermittently even when it tests good at parts stores. Testing under operational conditions is crucial; if the module is not pulsing the ignition coil correctly, it will prevent spark generation. Checking the module's voltage inputs and outputs while cranking the engine is essential for confirmation. - Static voltage reading on coil negative terminal during cranking, no spark detected at ignition coil.
- Distributor Mechanical Failure: The distributor's internal components, such as the rotor and cap, can wear out or become corroded. Even if the distributor appears intact externally, internal faults could prevent proper spark distribution. Testing the rotor's movement while cranking the engine can confirm its operational integrity. - Visible wear on rotor or cap, inconsistent rotor movement while cranking.
- Ignition Coil Issues: Even after installing a new ignition coil, the coil could be defective or not receiving proper voltage. Testing the positive and negative terminals for voltage while cranking can help determine if the coil is functioning correctly. The expected voltage at the positive terminal should be battery voltage, while the negative terminal should pulse during cranking. - New ignition coil installed but no spark; voltage checks show static reading on negative terminal.
- Electrical Connection Issues: Given the car's history of sitting outside, corrosion can occur at various electrical connections. Poor connections can lead to insufficient voltage to the ignition components. Ensuring all ground connections are clean and tight can help improve spark generation. - Corroded connections found during inspection; evidence of electrical arcing.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Voltage Check at Ignition Coil: Use a multimeter to check the voltage on the positive terminal (white/red wire) of the ignition coil while turning the ignition key to the ON position. You should see battery voltage present. If voltage is confirmed, proceed to check the negative terminal while cranking the engine to see if it pulses.
- STEP 2 - TFI Module Testing: Remove the TFI module and inspect for any signs of overheating or damage. If possible, conduct a bench test under load conditions, or consider replacing it with a known good unit to see if spark is generated.
- STEP 3 - Distributor Inspection: Remove the distributor cap and check for wear on the rotor and cap contacts. Ensure the rotor is turning when the engine is cranked by observing its movement. If there is significant wear or if it does not turn, replacement may be necessary.
- STEP 4 - Comprehensive Electrical Inspection: Inspect all electrical connections, especially grounds, for corrosion or looseness. Clean any corroded connections with a wire brush and ensure all connections are tight. This can often resolve intermittent ignition issues caused by poor connectivity.
