Where is the oxygen sensor located on a 1990 Ford Ranger 4 liter engine?

On a 1990 Ford Ranger with a 4.0L V6 engine, the oxygen sensor (O2 sensor) is typically located in the exhaust manifold, before the catalytic converter. There's usually one upstream (before the catalytic converter) and one downstream (after). However, the 1990 model likely only has the upstream sensor.

To be absolutely certain, you should:

* Consult your owner's manual: This is the best source of information specific to your vehicle.

* Check a repair manual specific to your year and engine: These manuals often have detailed diagrams showing sensor locations.

* Look under the vehicle: With the engine cool, carefully inspect the exhaust manifold and piping near the engine for a sensor with a wire harness connected to it. It will likely have a threaded body for installation into the exhaust.

Be aware that the location might vary slightly depending on specific options or modifications made to your truck. Use caution when looking underneath, as exhaust components get extremely hot.