Owner's Problem Description
The owner describes their 1990 Nissan Stanza as having run fine one day but failing to start the next. Despite replacing the starter, solenoid, rotor, distributor cap, and checking fuses and relays, the vehicle still does not start. There is no spark, and the fuel pump activates only when wired directly. The owner expresses desperation for assistance due to financial constraints.
Professional Technical Analysis
The 1990 Nissan Stanza with a KA24E engine (2.4L, approximately 150,000+ miles) is experiencing a crank no start condition. The owner has replaced several key components, including the starter and ignition-related parts, indicating a methodical approach to troubleshooting. Current symptoms include the absence of spark and the fuel pump engaging only when wired directly, suggesting issues within the control circuits. The lack of spark points towards potential failure in the ignition system, specifically the crankshaft position sensor (CKP) or camshaft position sensor (CMP) as critical components for starting the engine. The CKP sensor provides essential input for the Engine Control Module (ECM) to control ignition timing. Voltage specifications for the CKP sensor should be around 0.5V to 5V, depending on the RPM and operational status. Any significant deviation from this range may indicate sensor failure. An OBD-I scan is strongly recommended to check for stored fault codes, as these codes can provide insight into the malfunctioning components. If the sensors are not easily accessible, a manual resistance check can be performed; the CKP sensor should typically show a resistance between 200-800 ohms. Current vehicle condition is critical, as continued cranking without spark can lead to battery drain and additional strain on the starter system. The previous repair history suggests that the owner has taken reasonable steps, but systematic diagnosis is essential to avoid further unnecessary costs.
Possible Causes
Most common causes (ordered by frequency):
- Crankshaft Position Sensor (CKP) Failure: The CKP sensor is crucial for providing the ECM with the position of the crankshaft, which is essential for ignition timing. A failure in this sensor can lead to no spark, preventing the engine from starting. Typically, the CKP should output a voltage range of 0.5V to 5V, which changes based on the RPM. A resistance check should reveal values between 200-800 ohms. If the sensor is faulty, replacement with OEM part number 23731-0F401 is recommended, costing approximately $50-100. - No spark at the ignition system, resistance measurement outside of specified range, potential stored fault codes related to CKP.
- Camshaft Position Sensor (CMP) Failure: The CMP sensor works in conjunction with the CKP sensor to provide the ECM with necessary data for proper fuel injection and ignition timing. A failure in the CMP sensor can also lead to no spark conditions. The CMP sensor should show similar resistance values as the CKP sensor, and if faulty, replacement with OEM part number 23731-0F401 is suggested at a cost of $50-100. - No spark at the ignition system, potential stored fault codes related to CMP, resistance measurement outside of specified range.
- ECM Malfunction: If both the CKP and CMP sensors are functioning correctly, a malfunction within the ECM may prevent spark generation. The ECM should receive the signals from both sensors to operate the ignition system. A diagnostic scan can reveal ECM-related fault codes. Replacement is typically costly, around $300-600 for an OEM unit. - Stored fault codes indicating ECM issues, lack of response from ignition system despite proper sensor input.
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-I Diagnostics: Connect an OBD-I scanner to retrieve any stored fault codes. This step is crucial as it can provide insight into specific sensor failures or ECM issues. If no codes are present, proceed to manually check the CKP and CMP sensors.
- STEP 2 - Sensor Resistance Testing: Use a digital multimeter to measure the resistance of the CKP and CMP sensors. Both sensors should provide readings between 200-800 ohms. If readings are outside this range, the sensors should be replaced.
- STEP 3 - Voltage Signal Testing: With the ignition in the ON position, check the voltage output of the CKP and CMP sensors. The voltage should vary between 0.5V and 5V as the engine cranks. If there is no voltage output, the sensor is likely faulty.
- STEP 4 - Inspect Wiring and Connectors: Visually inspect the wiring and connectors leading to the CKP and CMP sensors for any signs of damage or corrosion. Poor connections can lead to sensor failures and should be repaired if found.
