Learn about your LTG - Evap System

Written By LTG Motorworks .

While the turbo makes the LTG fast, and the ignition and fuel systems make it powerful, the EVAP system makes it clean. It’s not a performance part in the traditional sense, but it plays a vital role in both emissions compliance and overall efficiency. In fact, without a properly working EVAP system, you can trigger check engine lights, fail emissions tests, and even lose a little fuel economy.

The EVAP system’s mission is simple: capture fuel vapors before they escape into the atmosphere, store them safely, and send them back into the engine to be burned. It’s a closed loop that prevents waste and reduces environmental pollution — and in a turbocharged direct-injection setup like the LTG, it’s engineered with special safeguards to handle boost pressure.

1. Key Components of the LTG EVAP System

1. EVAP Purge Solenoid Valve

  • Acts like a controlled gateway from the EVAP canister to the intake manifold.

  • Commanded by the ECM to open under specific conditions, allowing vapors to be drawn into the engine for combustion.

2. EVAP Canister

  • Packed with activated carbon pellets that absorb and store fuel vapors from the tank.

  • Holds vapors until the ECM decides it’s time to purge them.

3. EVAP Vapor Tube

  • Connects the fuel tank to the canister, letting vapors flow for storage.

4. Vapor Recirculation Tube

  • Provides access points for diagnostics, allowing techs (or DIYers) to run leak and restriction tests.

5. Fuel Tank Pressure Sensor

  • Monitors vacuum or pressure in the fuel tank.

  • Sends feedback to the ECM to verify system performance and detect leaks.

6. Fuel Filler Cap or Capless Fill Design

  • Seals the system after fueling.

  • Capless systems simplify filling but still maintain a secure seal.

7. Fuel Fill Pipe Inlet Check Valve

  • Stops fuel from splashing back out during refueling.

8. Fuel Tank

  • Stores liquid fuel, which naturally creates vapors that need to be captured.

9. EVAP Canister Vent Solenoid Valve

  • Controls when fresh air is drawn into the canister during purging or testing cycles.

10. Vent Hose

  • Provides a path for pressure equalization with the atmosphere when commanded.

11. EVAP Purge Tube

  • Carries vapor from the canister to the intake manifold under vacuum.

12. Purge Tube Check Valve (Turbo-Specific)

  • Prevents boost pressure from entering the EVAP system, which could damage components or cause leaks.

2. How the EVAP System Works

  1. Vapor Capture – As fuel warms and moves inside the tank, vapors travel through the vapor tube into the carbon-filled EVAP canister.

  2. Storage – The canister traps and holds these vapors until the ECM schedules a purge.

  3. Purge Cycle – Under certain load and temperature conditions, the ECM opens the purge solenoid, allowing engine vacuum to draw vapors from the canister into the intake manifold.

  4. Combustion – Vapors mix with incoming air/fuel and are burned in the cylinders, reducing waste.

3. Diagnostic and Testing Functions

The ECM runs a variety of tests to ensure the EVAP system is sealed and functioning:

  • Purge Solenoid Valve Leak Test – Ensures the valve isn’t stuck open or closed.

  • Large Leak Test – Looks for major breaches, like a loose fuel cap.

  • Small Leak Test – Detects pinhole leaks in hoses or seals.

  • Canister Vent Restriction Test – Checks for blockages that could prevent fresh air flow.

If any of these fail, a check engine light will trigger — common codes include P0440, P0442, P0455, and P0496.

4. LTG-Specific Considerations

Because the LTG is turbocharged, the EVAP system includes a purge tube check valve to stop boost from entering the canister. Without it, pressure could force vapors backward or damage seals.

  • This is a common point of failure if the valve sticks or leaks — symptoms include rough idle after fill-ups or EVAP codes.

  • Always use a turbo-rated check valve when replacing this part.

5. DIY Maintenance Tips

  • Check the Cap First: A loose or damaged fuel cap is the #1 cause of EVAP codes.

  • Listen for Purge Operation: A faint ticking from the purge solenoid during idle warm-up is normal.

  • Smoke Testing: A DIY smoke machine can help find small leaks in hoses or seals.

  • Boost-Proof the System: If running higher boost, inspect the purge tube check valve more often — more pressure means more wear.

LTG Motorworks .
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