Owner's Problem Description
The owner's 1995 Dodge Intrepid with a 3.5L engine and approximately 175,000 miles suddenly died. There is fuel pressure, and the ignition coil checks out fine. However, it only sparks once from the #1 spark plug when cranking. After replacing the crankshaft position sensor (CRPS), the issue persists. The owner suspects the cam sensor or a timing belt issue, as they can hear the valves operating, but is also considering the MAP sensor's role. They are hesitant to spend more money without a clear diagnosis.
Professional Technical Analysis
The 1995 Dodge Intrepid, equipped with a 3.5L V6 engine and approximately 175,000 miles, presents a no-start condition. Initial diagnostics reveal fuel pressure at the check valve, indicating the fuel pump is operational. Ignition coil testing shows appropriate voltage, yet spark is only observed once at the #1 plug during cranking. This suggests a potential issue with the ignition control system. The crankshaft position sensor (CRPS) has been replaced, but the problem persists, indicating that the fault may lie elsewhere. The owner speculates on a possible camshaft position sensor failure or a timing belt issue, though valve operation sounds normal. The intermittent spark suggests an underlying electrical issue, possibly linked to the Auto Shut Down (ASD) relay, which could affect both fuel pump and ignition coil operation. Analyzing the electrical system for voltage drops and verifying the integrity of connections is crucial. Given the vehicle's age and mileage, components like the ignition control module (ICM) or the MAP sensor should also be assessed, as these have known failure patterns that could lead to similar symptoms. Current vehicle conditions indicate a need for a systematic diagnostic approach to isolate the fault, ensuring any safety concerns are addressed.
Possible Causes
Most common causes (ordered by frequency):
- Ignition Control Module (ICM) failure: The ICM may be failing due to heat or age, common in high-mileage vehicles. This could lead to intermittent spark issues. Testing should include checking for proper input and output signals. Typical failure modes include failure to provide spark under load, which can be verified through live data monitoring. ICM for this vehicle typically has a resistance of 1-2 ohms on the primary side and should output a signal voltage of 5V when functioning correctly. Replacement ICMs range from $100 to $250 depending on OEM or aftermarket sourcing. - Check engine light could be triggered, intermittent spark pattern observed, possible stored fault codes related to ignition.
- Camshaft Position Sensor (CMP) failure: A faulty CMP sensor can lead to improper ignition timing, which would result in no spark or incorrect spark timing. This sensor should produce a square wave signal, typically around 5V, when functioning properly. If it fails, the PCM might not receive the correct timing information. Testing should include checking the sensor output with an oscilloscope for signal integrity. Replacement CMP sensors can cost between $50-$150. - Symptoms include no spark under cranking conditions, potential stored codes for CMP malfunction.
- Auto Shut Down (ASD) Relay failure: The ASD relay controls power to the ignition coil and fuel pump, and a malfunction can result in a lack of spark and fuel delivery. Testing should involve checking the relay for continuity and operation under load. If the relay fails, it may need to be replaced, which typically costs around $30-$60. A faulty relay can be visually inspected for signs of burn or corrosion. - No fuel pump operation noted during cranking, potential voltage drops observed across the relay terminals.
- MAP Sensor failure: A malfunctioning MAP sensor may send incorrect pressure readings to the PCM, causing improper fuel metering and no start conditions. Testing the MAP sensor involves checking the voltage signal, which should range from 1V (idle) to 4.5V (wide open throttle). Replacement MAP sensors typically cost between $40-$100. - Poor fuel metering symptoms may be present, with potential error codes related to the MAP sensor.
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 - OBD-II Scan: Use a professional OBD-II scanner or GeekOBD APP to retrieve any stored fault codes. Since the battery was drained, it is crucial to check if any codes have been logged before the reset. Pay attention to engine-related codes, particularly those that could indicate ignition or sensor issues.
- STEP 2 - Fuel Pressure Check: Verify the fuel pressure using a fuel pressure gauge. The desired fuel pressure for this vehicle should be maintained between 35-45 PSI. If the pressure is below this range, it may indicate a failing fuel pump or clogged fuel filter. Document the readings for future reference.
- STEP 3 - Spark Testing: Check for spark at the ignition coil and the #1 spark plug. Use a spark tester to verify if the spark is consistent during cranking. If spark is intermittent or absent, proceed to check the ICM and CMP sensor outputs for proper signal integrity.
- STEP 4 - Relay and Sensor Testing: Inspect the ASD relay for continuity and proper operation. Test the MAP sensor output using a multimeter, ensuring it provides expected voltage readings under various engine conditions. Replace any faulty components identified during testing.
