Owner's Problem Description
The owner reports that their 1998 Chevy Cheyenne truck has developed a starting issue over the past year. The truck often fails to start when it's cold and wet, although it turns over. Typically, it starts by the afternoon. Recently, the owner has noticed it cutting out intermittently. They suspect the moisture might be causing the issue and have tried covering the hood with a blanket, which seems to help. The problem persists, especially in winter conditions.
Professional Technical Analysis
This 1998 Chevy Cheyenne truck, equipped with a 5.7L V8 engine and an automatic transmission, has approximately 180,000 miles on it. The owner reports intermittent starting issues, particularly in cold and wet conditions. The engine turns over but fails to start, which suggests a potential ignition or fuel system issue. Given the owner's observation that covering the hood helps, moisture ingress is a likely factor. The truck also shows signs of occasional stalling, indicating possible electrical or fuel delivery failures. Components such as the ignition control module (ICM), fuel pump, and mass air flow (MAF) sensor must be evaluated, alongside the battery and ground cables. The voltage supply should be verified, as poor connections can lead to starting issues. A thorough diagnostic using the GeekOBD APP to monitor live data during starting attempts will aid in pinpointing the root cause. In my experience, common failure points include poor electrical connections at the ignition coil, moisture-related failures in the ICM, or fuel delivery issues due to a failing fuel pump. Safety should be prioritized, especially as the vehicle is cutting out while driving.
Possible Causes
Most common causes (ordered by frequency):
- Moisture-Related Ignition Control Module (ICM) Failure: The ICM, often located near the engine or firewall, can fail due to moisture ingress, especially in cold, damp conditions. This module typically fails to provide a spark when wet, leading to no-start conditions. The ICM should be tested for proper output voltage (typically around 12V during crank) and checked for moisture damage. If it fails under these conditions, consider replacing it with OEM P/N 10456126. - Symptoms include failure to start on cold, wet days, intermittent stalling, and voltage drops at the ICM during testing.
- Fuel System Issues: If the fuel pump isn’t priming correctly, or if there’s a clog in the fuel filter, it could prevent starting in cold, damp conditions. The fuel pump should be checked for proper operation, with pressure readings expected between 60-65 PSI. If the pump is faulty, replace it with OEM P/N 19117150. - No fuel pressure during crank, fuel pump relays clicking but not engaging, and check engine light indicating fuel system errors.
- Electrical Connection Problems: Corrosion or loose connections at the battery terminals, ground connections, or wiring harness can lead to insufficient power to the ignition system and fuel pump. Tightening and cleaning these connections can often resolve intermittent starting issues. Ground connections should show less than 5 ohms resistance. - Visual inspection of battery terminals shows corrosion, and ground cables show signs of wear.
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 Scan with GeekOBD APP: Begin by connecting the GeekOBD APP to the vehicle's OBD-II port to retrieve any stored fault codes. Pay particular attention to fuel system and ignition codes that may point to underlying issues. Use the app to monitor live data during the no-start condition to check fuel pressure and ignition signals.
- STEP 2 - Fuel System Pressure Test: Connect a fuel pressure gauge to the test port. Crank the engine and observe the fuel pressure, which should be within the range of 60-65 PSI. If the pressure is low or absent, suspect a fuel pump or filter issue. Check the power and ground connections to the fuel pump for integrity.
- STEP 3 - Visual Inspection of Electrical Connections: Inspect battery terminals, ground connections, and wiring harness for corrosion or loose connections. Clean any corroded connections and tighten them to ensure reliable electrical flow. Ground connections should be tested for resistance, aiming for less than 5 ohms.
- STEP 4 - Testing the Ignition Control Module: If issues persist, remove the ICM and perform a bench test to evaluate its output voltage while simulating operating conditions. Check for signs of moisture damage. If the module fails to provide a consistent spark or voltage, replace it with a new unit.
