December 14, 2023

Acura NSX (1995-2005) Check Engine Light or Running Rough?

Acura NSX EVAP check engine light and running rough or not starting A check engine light on your Acura NSX only tells have the story, if it’s running rough or not starting, we may have your answer.  Working on an Acura NSX, particularly 1995-2005 models, I’ve encountered my fair share of EVAP system issues. The first thing you’ll likely see is an engine light. I can’t imagine anything more frustrating than having this car and it running rough, or not starting at all.  Let’s take a look at how to troubleshoot and fix these issues, focusing on the EVAP control valves.

Brake fluid leak? Oil leak?

Check for Recalls

Understanding the EVAP System in Your Acura NSX

The Evaporative Emission Control System, captures gas vapors from the fuel tank and stores them in a charcoal canister safely burning them in the engine. This is required for the environment and improves your vehicle’s efficiency.

Role of EVAP Control Valves

The control valves manage the flow of vapors into the engine. If these valves fail, you’ll see a noticeable drop in fuel efficiency, increased emissions, and that dreaded engine light.  If your car is also not starting, then this is the issue.

Acura NSX symptoms

  • Check Engine Light: The most common symptom. Modern vehicles, including the Acura NSX, have an onboard diagnostic system that detects irregularities in the emissions system.
  • Fuel Odor: If the EVAP system is not sealing properly due to a faulty control valve, fuel vapors may escape, resulting in a noticeable gasoline smell.
  • Difficulty Starting the Engine: May cause issues with the fuel system pressure, leading to difficulties in starting the engine.
  • Poor Fuel Economy: May be less fuel efficient, resulting in a decrease in miles per gallon (km/l).
  • Performance: A faulty EVAP valve can cause performance issues such as rough idling, stalling, or hesitation during acceleration.
  • Failed Emissions Test: A malfunctioning valve can cause higher hydrocarbon emissions, which will fail an emissions test.

Troubleshooting

  • Engine Light.  The first sign is often the engine light. Use an OBD-II scanner to read the codes. Common codes include P0440, P0441, P0442, P0446, P0455, and P0456.  See all the OBD codes here.
  • Gas Cap.  A loose or faulty gas cap can trigger EVAP system codes. Check if it’s tight and in good condition.
  • Visible Signs of Damage.  Inspect the EVAP hoses and connections for cracks or loose fittings. Any damage here can cause leaks that affect the system’s performance.
  • Locate the EVAP Control Valve: It’s typically found near the fuel tank or the charcoal canister.
  • Test the EVAP Control Valves.  The control valves can be tested using a vacuum pump. If they don’t hold vacuum, they need to be replaced.
    • Visual Inspection:  Check for any signs of damage, cracks, or loose connections.
    • Disconnect the Valve:  Carefully disconnect the electrical connector and vacuum lines from the valve. Note how they were connected.
    • Test the Valve with a Multimeter:  Set your multimeter to the ohms (resistance) setting.  Connect the multimeter leads to the valve’s terminals.  A normal reading typically falls within a specific range, often between 20-30 ohms, but check your vehicle’s manual.
    • Perform a Vacuum Test:  Connect a hand-held vacuum pump to the valve’s port.  Apply vacuum to the valve and observe if it holds vacuum.
    • Check Valve Operation:  Reconnect the electrical connector to the valve.  Turn on the vehicle’s ignition (do not start the engine).  Use the multimeter in voltage mode to check if the valve is receiving voltage.  A functioning valve should receive voltage when the engine is idling (consult the vehicle manual for specifics).
    • Reconnect Everything:  Once testing is complete, reconnect all vacuum lines and electrical connections as they were originally.

Replacing Acura NSX Failed EVAP Control Valves

  • Disconnect the Battery.  For safety, disconnect the negative terminal of the battery.
  • Remove the Old Valves.  Disconnect the hoses and electrical connectors from the valves. Remove any mounting screws or clamps.
  • Install the New Valves.  Place the new valves in the same position as the old ones. Connect the hoses and electrical connectors.
  • Reconnect the Battery and Test.  Reconnect the battery and start the car. Check if the engine light turns off. It may be wise to drive for a few days to ensure the issue is resolved.

Final Thoughts

Your car is noticeably having issues… it may be running rough or just not starting. Dealing with EVAP system issues can be tough.  Hopefully this page make it manageable.  For NSX owners, I made this page to bring awareness of the EVAP system’s role and knowing how to address common issues. Stay vigilant for that engine light and happy motoring!

By following these steps and understanding the importance of the EVAP system, you can ensure your NSX runs smoothly and stays environmentally friendly.