Owner's Problem Description
The owner of a 1990 Mitsubishi Mirage with a 1.5L MPFI engine reports that the engine will not fire. They mentioned that the timing was confirmed to be good, but no further details about previous checks were provided. The vehicle's current condition shows no signs of starting, prompting a need for a thorough diagnostic process. The owner has not replaced any components recently and is seeking assistance in diagnosing the issue.
Professional Technical Analysis
This case involves a 1990 Mitsubishi Mirage with a 1.5L MPFI engine, likely having around 150,000 miles on the odometer. The owner reports that the engine will not fire, indicating a potential issue in the ignition or fuel delivery systems. Given the owner's assertion that the timing is good, it is crucial to confirm the operation of the ignition system first. The symptoms suggest that either the ignition system is not producing a spark, or the fuel system is not delivering fuel properly. A thorough investigation should include checking the distributor for rotation and ensuring that there is spark at the plugs. The interconnection of systems is essential here; if the timing belt has indeed failed, the distributor will not rotate, leading to a no-spark condition. Furthermore, the health of the fuel pump and delivery system must also be assessed, as a lack of fuel pressure can also lead to a no-start scenario. The current condition indicates that without spark or fuel, the engine cannot run, presenting a safety concern if the vehicle is attempted to be started repeatedly without proper diagnostics. Previous repairs or maintenance history should be reviewed for any alterations that may have affected the ignition or fuel systems. The potential for common failure modes in vehicles of this age also includes sensor malfunctions, wiring issues, or component fatigue, which must be considered when diagnosing the root cause.
Possible Causes
Most common causes (ordered by frequency):
- Timing Belt Failure: This could potentially be the primary issue if the timing belt has broken or slipped. If the distributor is not turning when the engine is cranked, this indicates a failure in the timing belt system. The belt should be inspected for integrity and proper tension. Typical symptoms of a failed timing belt include engine cranking without firing and an audible lack of valve movement. If the timing belt is broken, replacement is necessary (OEM P/N MD110116, cost approximately $100-$150). - No rotation of the distributor when cranking, possible sound of the engine cranking without firing.
- Ignition System Fault: The ignition coil could be faulty, or there might be issues with the ignition control module (ICM). If the coil is not providing sufficient voltage to the spark plugs, the engine will not fire. Testing the coil's primary and secondary resistance is essential (primary should be around 0.5-2 ohms, secondary 6,000-15,000 ohms). If the ICM fails, it often leads to a no-start condition. Typical replacement costs are $50-$150 for the coil (OEM P/N MD181768). - No spark detected at the spark plugs, possible stored codes related to ignition system failure.
- Fuel Delivery Issue: If the fuel pump is not functioning properly, fuel may not reach the engine. A fuel pressure test should be conducted to ensure it maintains the required pressure (typically 35-45 PSI). If pressure is below specifications, the fuel pump (OEM P/N MD614476) may need replacement, costing about $200-$300. - Low fuel pressure reading during tests, audible sound of the fuel pump not engaging.
- Wiring or Connector Issues: Corroded or damaged wiring and connectors can prevent voltage from reaching the ignition system or fuel pump. A thorough inspection of the wiring harness, especially around the ignition coil and fuel pump, should be conducted. Look for signs of wear, corrosion, or loose connections, which can lead to intermittent faults. - Visual inspection reveals corrosion at connectors, continuity tests show intermittent connection 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 - Visual Inspection: Begin with a thorough visual inspection of the engine bay. Look for any signs of broken components, particularly the timing belt cover. Check the integrity of wiring and connectors associated with the ignition and fuel systems. Pay attention to any signs of wear or corrosion that might affect connectivity.
- STEP 2 - Check Distributor Rotation: Remove the distributor cap and crank the engine. Observe if the rotor is turning. If not, this indicates a potential timing belt failure. If the rotor is turning, proceed to check for spark by removing a spark plug wire and using a screwdriver to check for spark against a grounded surface.
- STEP 3 - Fuel Pressure Test: If spark is detected, the next step is to check fuel pressure. Use a fuel pressure gauge connected to the fuel rail to verify that the pressure is within the range of 35-45 PSI. If pressure is low, this indicates a potential fuel pump issue.
- STEP 4 - Electrical System Testing: Conduct a comprehensive electrical check of the ignition system components including the ignition coil and ICM. Measure resistance values to ensure they are within specifications. Additionally, check for continuity in wiring and connectors leading to the fuel pump and ignition systems.
