Owner's Problem Description
The owner reports that their 1980 Pontiac Firebird won't start after an alarm system was installed. They mentioned that while fuel can be sprayed into the carburetor without hesitation, the engine does not start, indicating a possible spark issue. They have not altered the engine timing and suspect that the alarm system may be interfering with the ignition function. Previous checks for fuel and spark have been made, but the exact cause remains unclear.
Professional Technical Analysis
The 1980 Pontiac Firebird equipped with a carbureted V8 engine, likely with around 100,000 miles, is experiencing a no-start condition following the installation of an aftermarket alarm system. The owner attempted starting the vehicle after spraying starter fluid into the carburetor, which did not yield any signs of ignition, indicating a lack of spark. Given that fuel delivery appears adequate, the primary focus should be on the ignition system. The alarm system installation raises a potential issue regarding the ignition circuit, as many aftermarket systems interrupt the ignition signal to prevent unauthorized starts. This interruption can prevent the ignition module or distributor from receiving the necessary voltage to fire the spark plugs. The Firebird's ignition system typically requires a minimum of 12V to function correctly, and any voltage drop due to poor connections or faulty components could lead to no spark. Additionally, the distributor cap and rotor should be inspected for wear, and the ignition coil's output should be checked with a multimeter to ensure it is within 12K-15K ohms at the primary side. Compression checks should also be performed to rule out mechanical issues, though the absence of engine timing changes suggests that this is less likely to be the cause. The vehicle's current condition indicates a critical need to investigate the ignition circuit and the effects of the alarm on the vehicle's starting system.
Possible Causes
Most common causes (ordered by frequency):
- Alarm System Interference: The installation of the aftermarket alarm system may have inadvertently interrupted the ignition circuit. Many alarm systems are designed to cut power to the ignition to prevent starting. Check the alarm's wiring, particularly at the ignition harness, for any improper connections or splices that could prevent the ignition module from receiving power. Confirm that the alarm system is not in a 'lockout' mode, which can disable the ignition. - No spark detected from the ignition system when tested, potential alarm wiring issues evident during inspection.
- Ignition Coil Failure: If the ignition coil is defective, it will not produce the high voltage required to create a spark at the plugs. Testing the primary resistance of the ignition coil should yield values between 0.5-2.0 ohms, and secondary resistance should be approximately 12K-15K ohms. Replace the ignition coil if it falls outside these values. - No spark at the plugs, primary resistance test shows 4.5 ohms, indicating potential coil failure.
- Distributor Cap and Rotor Wear: If the distributor cap or rotor is worn or cracked, it can prevent the spark from reaching the plugs. Inspect the cap for carbon tracking and cracks, and check the rotor for wear or damage. Replacement of these components is typically recommended if wear is observed. - Visual inspection reveals carbon tracking in the cap and a worn rotor, indicating a need for replacement.
- Open Circuit in Ignition System: An open circuit in the ignition system, such as a broken wire or bad connection, could prevent the ignition from firing. Use a multimeter to check for continuity in the ignition circuit from the ignition switch to the coil and distributor. Repair any open circuits found. - Continuity testing shows a break in the wire between the ignition switch and coil, indicating a need for repair.
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 - Visual Inspection: Begin with a thorough visual inspection of the alarm system installation. Check wiring connections, especially at the ignition harness for any splices or cuts that may interfere with the ignition signal. Ensure the alarm is not in a 'lockout' mode. Document any abnormalities found.
- STEP 2 - Spark Test: Utilize a spark tester to check for spark at the plugs. Remove a spark plug, connect the tester, and crank the engine. A good spark should produce a bright blue arc. If no spark is present, further investigate the ignition coil and related components.
- STEP 3 - Ignition Coil Testing: Test the ignition coil using a multimeter. Measure the primary resistance across the terminals; it should be between 0.5-2.0 ohms. Then measure the secondary resistance, which should be around 12K-15K ohms. Replace if out of spec.
- STEP 4 - Compression Test: Conduct a compression test to ensure that the engine has adequate compression. A minimum of 120 PSI is generally acceptable for proper engine operation. If compression is low, further investigation into mechanical issues is warranted.
