Owner's Problem Description
The owner installed a 1990 Ford 5.0L 302 EFI engine in a 1941 Ford with a C-4 automatic transmission. After rebuilding the engine and replacing all sensors, including O2 sensors, trouble codes 42, 92, and 75 appeared during the KOER test, while KOEO test showed a pass code of 11. The owner questions if the lack of a Brake On/Off circuit is causing the issues and seeks further diagnostic guidance. The vehicle shows good compression and fuel pressure readings.
Professional Technical Analysis
In this case, we are analyzing a 1990 Ford Crown Victoria equipped with a 5.0L 302 EFI engine that has been retrofitted into a 1941 Ford chassis. The vehicle has been fully rebuilt, with new sensors and a remanufactured Engine Control Module (ECM) installed. The KOEO test returned a passing code of 11, while the KOER test revealed trouble codes 42, 92, and 75. Code 42 indicates a problem with the EGR (Exhaust Gas Recirculation) system, potentially due to a malfunctioning EGR valve or a vacuum leak. Code 92 relates to the fuel system, indicating a rich running condition often caused by incorrect fuel pressure or injector issues. Code 75, linked to the Brake On/Off circuit, may not directly cause the other codes but can complicate diagnostics. The engine exhibits 165 psi compression across all cylinders, 18 inches of vacuum at idle, and fuel pressures of 40 psi static and 30 psi running. These parameters suggest that the engine is mechanically sound, however, the fuel pressure should ideally be within the 30-45 psi range when running. The observed vacuum at idle is slightly lower than normal, typically around 20 inches, which could indicate potential intake leaks. Given the thorough replacement of vacuum hoses, it is crucial to verify the integrity of all connections, including the EGR system and any other air intake paths. The potential for a misconfigured ECM, specifically regarding the EGR and fuel system parameters, should be evaluated, as it might be looking for signals not present in the current setup.
Possible Causes
Most common causes (ordered by frequency):
- EGR System Malfunction: The EGR valve may be stuck open or partially clogged, causing the PCM to set code 42 due to insufficient vacuum or incorrect flow. Verify EGR operation by checking for vacuum at the EGR valve during operation; it should receive vacuum when the engine is at operating temperature and under load. If the EGR valve is defective, the part number is Ford OEM P/N F0AZ-9D475-A, with replacement costs estimated at $80-$120. - Presence of exhaust leaks, unusual idle characteristics, low vacuum readings during KOER test.
- Fuel System Rich Condition: The fuel pressure readings indicate 30 psi while running, which is on the lower end of the expected range (30-45 psi). This could suggest that the fuel pressure regulator (Ford OEM P/N F1AZ-9B263-A) is failing or that the fuel injectors are leaking. Test fuel pressure under load conditions to confirm that it can maintain adequate pressure; replacement costs for the regulator are around $100-$150. - Symptoms include rich running condition, possible black smoke from the exhaust, and poor fuel economy.
- ECM Configuration Issues: The ECM may not have been properly configured or programmed to operate without certain sensors, particularly the Brake On/Off circuit. This could lead to codes 42 and 92 appearing. Verify if the ECM requires reprogramming based on the current engine setup and configurations. Reprogramming services can vary in cost but generally range from $100-$200. - Engine performance issues, abnormal sensor readings, and codes present without corresponding sensor hardware.
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 OBD-II Scan: Utilize a professional OBD-II scanner or the GeekOBD APP to retrieve all trouble codes and freeze frame data. Pay attention to code 42 and 92, which are indicative of EGR and fuel system issues. Document any pending codes and perform a KOEO test to confirm the results.
- STEP 2 - Vacuum and Air Leak Testing: Inspect all vacuum lines and connections for leaks. Use a smoke machine to identify any hidden leaks in the intake system. Ensure that the EGR valve is functioning properly and that there are no obstructions in the passages.
- STEP 3 - Fuel Pressure Testing: Verify fuel pressure using a fuel pressure gauge. The static fuel pressure should be within 30-45 psi range at idle. If the pressure is low, test the fuel pressure regulator and injectors for leaks. Ensure all connections are secure.
- STEP 4 - EGR Function Verification: Check the operation of the EGR valve by applying vacuum to the diaphragm and observing the valve movement. It should open and allow exhaust flow when vacuum is applied. If it does not function correctly, consider replacement.
