Owner's Problem Description
The owner reports that their 1990 Oldsmobile Silhouette with a 3.1L engine flooded and won't start after a failed jump-start attempt in very cold weather (-30 degrees). Since then, both throttle body injectors are dumping excessive fuel. The owner has replaced the ECM and coolant temperature sensor, but the issue persists without any trouble codes being displayed. Fuel pressure regulator appears fine, but the engine idles roughly when one injector is disconnected, indicating a fuel delivery issue.
Professional Technical Analysis
The vehicle in question is a 1990 Oldsmobile Silhouette equipped with a 3.1L V6 engine, likely with over 150,000 miles given its age. After an unsuccessful jump-start attempt in extremely cold temperatures, the owner noted a severe flooding issue with both throttle body injectors dumping excessive fuel. This condition led to a no-start situation. The initial inspection revealed that the Electronic Control Module (ECM) and the coolant temperature sensor had been replaced, but no improvement was noted, and no trouble codes were stored in the OBD system. The fuel pressure regulator was inspected and seemed to be functioning correctly. However, the engine did exhibit rough idling characteristics when one of the fuel injectors was disconnected, suggesting an over-fueling issue. Considering the environmental conditions, the extreme cold may have exacerbated existing issues, such as fuel viscosity and injector performance. Potential system interconnections include how the ECM regulates fuel delivery based on sensor inputs and how a malfunctioning injector could lead to excessive fuel delivery. Without stored codes, diagnostic steps should focus on monitoring the injector pulse width and fuel pressure to determine if the ECM is commanding the injectors to operate outside of normal parameters. Additionally, the crankshaft position sensor should be evaluated, as intermittent failures can lead to incorrect fueling and timing adjustments, further complicating the start-up process.
Possible Causes
Most common causes (ordered by frequency):
- Throttle Body Injector Malfunction: Both throttle body injectors may be stuck open or leaking due to wear or contamination, causing excessive fuel delivery. This can lead to flooding and a no-start condition. Testing should involve checking the injector resistance (typically 12-16 ohms) and confirming they are not leaking fuel when de-energized. - Excessive fuel smell, rough idle when one injector is disconnected, fuel leaks visible around the throttle body area.
- ECM Calibration Issue: The ECM may not be calibrated correctly, leading to improper fuel delivery commands. This could happen if the ECM was replaced without the necessary reprogramming or if there are updates required for the vehicle's software. - No trouble codes present, issues persisting after ECM replacement, potential software update requirements.
- Fuel Pressure Regulator Failure: Although inspected and seemingly fine, the fuel pressure regulator may still be faulty, allowing excessive fuel to enter the intake manifold. Testing should include fuel pressure measurement, which should ideally be around 40-50 PSI with the engine running. - Fuel pressure gauge reading indicating excessive pressure, rough idle indicating fuel delivery issues.
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 - Initial Visual Inspection: Start with a thorough visual inspection of the throttle body and fuel injectors. Look for signs of fuel leakage around the injectors and throttle body. Verify the integrity of electrical connections to the injectors and ECM. Check for any physical damage or contamination that could affect injector operation.
- STEP 2 - Fuel Pressure Measurement: Use a fuel pressure gauge to measure the fuel pressure at the throttle body. The pressure should be within the specified range (around 40-50 PSI). If the pressure is too high, it may indicate a failing fuel pressure regulator. Document the pressure readings for further analysis.
- STEP 3 - Injector Operation Check: Disconnect the electrical connectors from the throttle body injectors. Use a noid light to check for injector pulse. This will confirm if the ECM is sending the proper signal to the injectors. If no pulse is detected, further diagnostic of the ECM or wiring harness may be necessary.
- STEP 4 - Injector Resistance Testing: Measure the resistance of each fuel injector using a multimeter. The resistance should typically be within 12-16 ohms. If any injector shows an open circuit or significantly different resistance, it should be replaced. This step is crucial in confirming injector health.
