Owner's Problem Description
The owner replaced the fuel pump on their 1995 Chevy Corsica, which now runs fine. However, the fuel injector fuse blows whenever they attempt to start the engine. Using a higher-rated fuse allows the engine to run for about a second before the fuse blows again. This issue began immediately after the fuel pump replacement.
Professional Technical Analysis
This 1995 Chevy Corsica, equipped with a 2.2L engine and an automatic transmission, has approximately 150,000 miles. Following a fuel pump replacement, the owner reports that the fuel injector fuse blows when attempting to start the engine. Initially, the fuel pump was replaced due to low fuel delivery issues, which may have exposed underlying electrical problems. The fuel injector circuit may have shorted due to improper installation of the new fuel pump wiring harness. This could indicate an issue within the injector circuit, such as a damaged wire or faulty injector causing excessive current draw. The fuse should ideally be rated at 15 amps, as per factory specifications. When the ignition is turned on, the fuel injector circuit should not be powered until the engine is cranked. If the fuse blows at key-on, it suggests a direct short, whereas blowing only during cranking points to a potential short within the injectors or wiring. A thorough inspection of the wiring from the fuel pump harness, including checking for pinched wires or improper connections, is crucial. Testing the resistance of each injector should yield a reading between 12-16 ohms. Any injector reading below this range may indicate a short or internal failure. If no shorts are found, further investigation into the PCM's control logic for the injectors is warranted, especially given the potential for cascading failures in the fuel system, which can lead to safety concerns due to stalling or fuel delivery issues.
Possible Causes
Most common causes (ordered by frequency):
- Wiring harness short: The owner mentioned that when reconnecting the fuel pump pigtail, there was insufficient slack, and they may have inadvertently damaged the wires. A bare wire could cause a short circuit in the injector circuit, leading to excessive current draw and blowing the fuse. Inspect the wiring harness for visible damage and ensure proper insulation. - Visual inspection of wiring reveals frayed insulation or pinched wires; fuse blows immediately upon key-on.
- Defective fuel injector: An injector that has failed internally can create a short circuit condition, drawing too much current and blowing the fuse. Each injector should be tested for resistance, which should be between 12-16 ohms. An injector reading below this range indicates a possible short or failure. - Resistance testing shows one or more injectors with readings below 12 ohms; engine runs only briefly before fuse blows.
- Incorrect wiring connections: If the fuel pump was connected incorrectly, it might have affected the circuit integrity of the fuel injector system. This could lead to a miswired injector circuit, causing shorts and fuse blows. Review wiring diagrams to ensure all connections are correct. - Inspection of the wiring connection points shows mismatched colors or incorrect pin placement; fuse blows during starting.
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: Begin with a thorough visual inspection of the fuel pump wiring harness, especially the pigtail connections. Look for any signs of fraying, exposed wires, or improper connections. If the wires look damaged, repair or replace the harness as necessary.
- STEP 2 - Injector Resistance Testing: Disconnect the injector connectors and use a multimeter to measure the resistance of each injector. Each should read between 12-16 ohms. Document any injectors that fall outside this range for further testing or replacement.
- STEP 3 - Wiring Continuity Test: Perform a continuity test on the wiring from the fuel pump to the fuel injectors. Use the multimeter to check for any shorts or opens in the circuit. Ensure continuity exists without any resistance that could indicate a short.
- STEP 4 - Key-on Testing: With the ignition in the 'ON' position (engine not running), observe whether the injector fuse blows. This will indicate if a short is present without cranking the engine. If it holds, proceed with cranking the engine to check for fuse integrity during operation.
