Owner's Problem Description
The owner of a 1973 Buick Centurion with a 455 engine reports that the car starts without issue when cold. However, after running and warming up, starting becomes problematic. After stopping the engine for a few minutes, the car sometimes fails to crank when attempting to start, producing a low grunt sound. Releasing the key and trying again usually results in a successful start. Additionally, the gas pedal sticks and requires force to depress, although the owner is unsure if this is related. Assistance is sought to diagnose these issues.
Professional Technical Analysis
The 1973 Buick Centurion equipped with a 455 engine and approximately 100,000 miles is experiencing intermittent starting problems, particularly when warm. The owner notes that while the vehicle starts easily when cold, it can struggle to crank after operating for a period. The grunt sound during cranking indicates potential issues with the starter motor or electrical connections, particularly under heat conditions. With the symptoms occurring after running, the heat may be affecting the starter's performance or its engagement with the flywheel. Additionally, the sticking gas pedal suggests possible binding in the throttle cable, which could be contributing to the starting issue by preventing the throttle from opening correctly. A comprehensive analysis of the starting system, including battery voltage under load (should be 12.4-12.6V at rest and above 10.5V during cranking), starter solenoid function, and the integrity of the starter motor is essential. It's crucial to check the starter for overheating signs, as the starter may not disengage properly due to thermal expansion, leading to the grunt sound. Furthermore, assessing the throttle cable for wear or corrosion and ensuring proper lubrication could alleviate the pedal issue and improve overall throttle response.
Possible Causes
Most common causes (ordered by frequency):
- Starter Motor Thermal Overheating: The starter motor may be overheating after prolonged use, leading to failure to engage properly when hot. Symptoms include a low grunt sound and inability to crank. Measure battery voltage during cranking; it should remain above 10.5V. If voltage drops significantly, it indicates a weak starter or poor electrical connections. - Low grunt sound during cranking, successful start after releasing key, battery voltage drops below 10.5V during cranking.
- Weak Starter Solenoid Engagement: The solenoid may not be engaging the starter properly when warm, possibly due to heat expansion or internal wear. Inspect the solenoid for proper operation and test the resistance across the solenoid terminals, which should be less than 0.5 ohms when activated. - Intermittent engagement of the starter, resistance testing showing values higher than normal.
- Throttle Cable Binding: The gas pedal sticking issue may indicate binding in the throttle cable, which can affect throttle response and starting conditions. Inspect the throttle cable for lubrication points and ensure it moves freely; use graphite or transmission fluid for lubrication. - Gas pedal sticks before start-up, requiring force to depress; throttle cable inspection shows 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 Electrical System Check: Begin by checking battery voltage and connections. Ensure the battery voltage is above 12.4V at rest and check for corrosion on terminals. Use a multimeter to measure voltage during cranking. Cleaning any corroded connections can improve starter performance. Consider using the GeekOBD APP to monitor battery health and potential pending codes.
- STEP 2 - Starter Motor Inspection: Remove the starter motor for inspection. Check the solenoid operation and test the resistance across the terminals. Ensure proper engagement with the flywheel. If the starter shows signs of overheating or wear, consider replacement. Document findings for future reference.
- STEP 3 - Throttle Cable Examination: Inspect the throttle cable for any signs of binding or wear. Lubricate as needed with appropriate lubricants like graphite or transmission fluid. Ensure that the throttle moves freely during operation. A properly functioning throttle can assist in smooth starting conditions.
- STEP 4 - Test Drive with Data Monitoring: After completing the inspections and any necessary repairs, take the vehicle for a test drive while monitoring the starting performance. Use the GeekOBD APP to log any diagnostic data and check for any recurring issues after the vehicle has warmed up.
