Possible Causes:
* Ignition System Issues:
* Spark Plugs and Wires: Worn or fouled spark plugs can misfire, causing jerking. Inspect for wear, corrosion, or gaps outside the recommended range.
* Distributor Cap and Rotor: Cracks or wear in the distributor cap or rotor can disrupt spark delivery.
* Ignition Coil: A failing ignition coil can deliver weak or inconsistent spark.
* Ignition Control Module: This module can fail, disrupting timing and causing misfires.
* Fuel System Problems:
* Fuel Filter: A clogged fuel filter restricts fuel flow, leading to uneven fuel delivery.
* Fuel Pump: A weak fuel pump can struggle to deliver enough fuel under acceleration.
* Fuel Injectors: Clogged or worn injectors can lead to inconsistent fuel delivery.
* Transmission Issues:
* Torque Converter: A slipping torque converter can cause jerking during acceleration.
* Transmission Fluid: Low or contaminated transmission fluid can cause problems with shifting.
* Engine Problems:
* Vacuum Leaks: Leaks in the vacuum system can disrupt engine timing or air/fuel ratios.
* Engine Sensors: Faulty sensors (like the Oxygen Sensor, MAP sensor, or TPS) can provide inaccurate readings, causing the engine to run poorly.
* Drivetrain Problems:
* U-Joints: Worn U-joints in the driveshafts can cause vibration and jerking during acceleration.
* Transfer Case: Issues with the transfer case, especially in a 4x4 vehicle, can lead to drivetrain problems.
Troubleshooting Steps:
1. Check Engine Light: If the Check Engine Light is on, use an OBD-II scanner to read the codes. This can provide valuable clues about the problem.
2. Inspect Spark Plugs and Wires: Visually inspect the spark plugs and wires for wear, corrosion, or signs of arcing. Replace them if necessary.
3. Check Fuel Filter: Replace the fuel filter if it's been a while or if you suspect it might be clogged.
4. Test Fuel Pressure: Measure the fuel pressure to see if the pump is delivering adequate pressure.
5. Check Transmission Fluid: Check the transmission fluid level and condition. Replace it if necessary.
6. Inspect Vacuum Lines: Look for any cracks, leaks, or disconnected hoses in the vacuum system.
7. Check for Engine Sensor Problems: Test the relevant engine sensors with a multimeter.
8. Inspect U-Joints and Driveline: Inspect the U-joints for wear and looseness.
9. Check for Transfer Case Issues: If you suspect transfer case problems, it's best to have it inspected by a qualified mechanic.
Important Notes:
* Safety First: Always work on a cool engine and disconnect the battery before working on electrical components.
* Professional Assistance: If you're not comfortable with vehicle repairs, it's best to take your Blazer to a qualified mechanic for diagnosis and repair.
By carefully troubleshooting the potential causes, you should be able to identify and resolve the jerking issue in your 1985 Chevy Blazer.
