Location: The most common location for the single O2 sensor on this engine is in the exhaust manifold or the Y-pipe (the pipe connecting the exhaust manifolds) near the catalytic converter. It's not accessible from inside the driver's compartment.
Changing the O2 Sensor:
1. Safety First: Disconnect the negative terminal of your battery before starting any work. This prevents accidental shorts and electrical damage. Allow the exhaust system to cool completely before you start working – it gets extremely hot.
2. Locate the Sensor: Crawl under the van. Look for a threaded sensor usually located close to the catalytic converter, in either the exhaust manifold or the Y-pipe. It will likely have a single wire (or sometimes a few) connected to it, and have a cylindrical shape.
3. Disconnect the Wiring Harness: Carefully disconnect the electrical connector from the O2 sensor. There's usually a small tab or latch to release the connector.
4. Remove the Sensor: You'll need an oxygen sensor socket. These are specifically designed to prevent rounding off the sensor's hex head. A standard socket might work but risks damaging the sensor. Apply penetrating oil (like PB Blaster) to the sensor threads a few hours before you start the work. This will loosen any corrosion.
Use the socket and a wrench to carefully unscrew the sensor. It may be quite tight due to heat and corrosion. Use gentle but firm pressure; if it's very stuck, consider using a breaker bar for extra leverage.
5. Install the New Sensor: Apply a thin layer of anti-seize compound to the threads of the new sensor. This prevents future corrosion and makes it easier to remove next time. Screw the new sensor into place by hand first, then tighten it with the oxygen sensor socket to the manufacturer's specified torque (consult your repair manual). Don't overtighten.
6. Reconnect the Wiring Harness: Securely reconnect the wiring harness to the new O2 sensor.
7. Reconnect the Battery: Reconnect the negative battery terminal.
8. Clear Trouble Codes (Optional): If you had a check engine light on before replacing the sensor, you might need to clear the trouble codes using an OBD-II scanner. Some auto parts stores will do this for free.
Important Notes:
* Repair Manual: A repair manual specific to your 1990 GMC Vandura 3500 is highly recommended. It will provide detailed diagrams, torque specifications, and other valuable information.
* Difficulty: This job can be challenging due to limited space under the van and the potential for stuck or corroded sensors. If you're uncomfortable working under your vehicle, consider taking it to a mechanic.
If you're still unsure about the location or the procedure, it's always best to consult a professional mechanic. Incorrect installation can lead to damage to the sensor, exhaust system, or even to your engine's performance.
