Possible Causes:
* Vacuum Leaks: A significant vacuum leak can cause erratic fuel/air mixture delivery, leading to backfires. Check all vacuum lines, the intake manifold gasket, and the throttle body gasket for cracks or leaks. Use a vacuum gauge to test the system's vacuum.
* Ignition System Problems:
* Worn distributor cap and rotor: These components wear over time and can cause misfires that lead to backfires. Inspect them for cracks, arcing, or wear.
* Worn or faulty spark plugs and wires: Check the spark plugs for proper gap, wear, and fouling. Inspect the spark plug wires for cracks, damage, or loose connections. A bad wire can cause a misfire in one or more cylinders.
* Ignition coil: A failing ignition coil can provide insufficient spark, resulting in misfires and backfires.
* Ignition module (control module): This controls the ignition timing and can fail, leading to erratic ignition.
* Crankshaft Position Sensor (CKP): A faulty CKP sensor will provide inaccurate signals to the ECM, affecting timing and potentially causing misfires.
* Fuel System Issues:
* Fuel injectors: A sticking or leaking fuel injector can deliver too much fuel, resulting in a rich mixture and potential backfires.
* Fuel pressure regulator: A faulty regulator can lead to incorrect fuel pressure, causing a rich or lean condition.
* Throttle Position Sensor (TPS): An inaccurate TPS reading can confuse the ECM, resulting in incorrect fuel delivery.
* MAF sensor (if equipped): A faulty Mass Airflow Sensor will provide incorrect airflow readings leading to improper fuel/air ratios. The 1990 Suburban might not have a MAF sensor; check your specific model specs.
* ECM/PCM Problems: While less common, a faulty Engine Control Module (ECM) or Powertrain Control Module (PCM) can cause malfunctions in the ignition and fuel systems, resulting in backfires.
Troubleshooting Steps:
1. Safety First: Don't continue to run the engine if it's backfiring through the throttle body. This is dangerous.
2. Visual Inspection: Begin by carefully inspecting all components mentioned above. Look for obvious signs of damage, wear, or loose connections.
3. Vacuum Test: Use a vacuum gauge to measure the manifold vacuum. Low vacuum indicates a leak.
4. Check Spark: Inspect the spark plugs and wires. If possible, use a spark tester to verify the spark strength.
5. Fuel Pressure Test: Check the fuel pressure using a fuel pressure gauge. Compare your reading to the specifications in your repair manual.
6. Scan the Codes: Use a code reader to check for any diagnostic trouble codes (DTCs) stored in the ECM. These codes can provide valuable clues to the problem.
7. Professional Help: If you're not comfortable troubleshooting these issues yourself, take your Suburban to a qualified mechanic specializing in older GM vehicles. This is crucial for safety and proper diagnosis.
Important Note: Backfiring can cause damage to engine components. Addressing the problem promptly is critical to prevent further damage and ensure the safety of yourself and others. If you are unsure about any of these steps, seek professional help immediately.
