Owner's Problem Description
The owner reports that their 1991 Dodge Shadow died after hitting a pothole. They checked the fuse for the fuel pump and found no power. Additionally, they noticed the light under the hood isn’t working. They replaced the auto shutoff relay but still have no power at the fuel pump fuse. The vehicle runs briefly when starting fluid is sprayed into the throttle body, indicating potential fuel delivery issues.
Professional Technical Analysis
The 1991 Dodge Shadow is equipped with a 2.5L inline-4 engine and has approximately 150,000 miles on the odometer. The owner's report of an intermittent stall following a pothole incident suggests potential electrical or fuel system failure. The absence of power at the fuel pump fuse indicates an issue in the circuit, which could be due to a faulty relay, wiring issue, or a failure in the engine control module (ECM) signaling. Given that the vehicle operates when starting fluid is applied, the ignition system is likely functional, focusing attention on the fuel delivery system. The ASD (Auto Shut Down) relay plays a critical role in powering the fuel pump; therefore, confirming the integrity of the relay and associated wiring is essential. A thorough check should include verifying the relay pinouts with a multimeter, ensuring the relay receives an activation signal from the PCM, and inspecting the wiring harness for damage or disconnections. Additionally, the inoperative hood light may be a symptom of a blown fuse or an issue with the vehicle's electrical system, warranting further investigation. Current vehicle conditions raise safety concerns due to potential stalling issues while driving.
Possible Causes
Most common causes (ordered by frequency):
- ASD Relay Failure: The Auto Shut Down relay may not be activating due to internal failure or loss of signal from the PCM. This relay is critical for supplying power to the fuel pump circuit. A multimeter should be used to check for voltage at the relay's coil terminals (should have battery voltage when the ignition is on), and also verify that the relay is properly seated and free from corrosion. Relay replacements typically range from $20 to $50. - No power at the fuel pump fuse, new ASD relay installed but still no voltage, multimeter shows no voltage at relay coil.
- Wiring Issues: The wiring from the ASD relay to the fuel pump may have been damaged due to the impact from the pothole, resulting in an open circuit. A visual inspection of the wiring harness and connectors is necessary to identify any signs of damage, broken wires, or corrosion. Continuity testing should be performed to ensure the circuit is intact. - Damaged wiring or connectors may be visible, continuity test reveals open circuit.
- Fuel Pump Failure: If the fuel pump itself has failed, it would not receive power despite the relay functioning correctly. Testing the fuel pump directly by applying battery voltage to it can confirm its operation. Fuel pumps typically fail after 100,000 miles due to wear, and replacement costs usually range from $200 to $400. - Fuel pump does not operate when powered directly, signs of wear or age may be evident.
- PCM Failure: A malfunction in the Powertrain Control Module (PCM) could prevent the ASD relay from receiving the activation signal. Checking for stored trouble codes related to the fuel pump and verifying PCM operation is critical. If the PCM is faulty, replacement can be costly, typically around $700 to $1200. - No trouble codes related to fuel pump or relay, PCM not responding during tests.
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 - Check Power at ASD Relay: Begin with a multimeter to check for power at the ASD relay. Ensure that the relay is receiving battery voltage at its coil terminals when the ignition is on. If no voltage is present, check the ignition switch and wiring leading to the relay.
- STEP 2 - Inspect Wiring and Connectors: Visually inspect the wiring harness and connectors from the ASD relay to the fuel pump for damage, corrosion, or loose connections. Perform continuity tests on the wiring to confirm no breaks or opens exist in the circuit.
- STEP 3 - Test Fuel Pump Operation: If the relay and wiring are in good condition, directly test the fuel pump by applying battery voltage. If it operates, the issue lies upstream with the relay or the PCM. If it does not operate, the fuel pump itself may need replacement.
- STEP 4 - Check for PCM Issues: If all previous checks pass, check for trouble codes using an OBD-II scanner. Confirm that the PCM is functioning correctly and providing signals to the ASD relay. If the PCM shows faults, further diagnostics will be necessary.
