Vapor Trapper Installation Guide

Vapor Trapper trunk-mounted routing diagram showing canister mount under body panel, fuel tank vent connection, vent line rising above highest point of liquid fuel, and atmospheric exit from trunk — Trunk-mounted routing (typical classic/muscle car)

The Vapor Trapper installs on most gasoline fuel systems in a few hours with hand tools. This is the universal version of the install — vehicle-specific notes (Mustang, Camaro, Jeep, etc.) are linked at the bottom and worth reading before you start if there is one for your platform.

Tools and parts

Vapor Trapper canister
3/8" fuel-rated vapor hose (sometimes labeled "evap hose" or "fuel vapor hose")
Worm-gear or fuel-injection clamps
Non-vented gas cap, or a plug to block the vent in your existing cap
Vacuum tee for the purge line connection
Bulkhead barb fitting for the tank vent (if drilling the filler neck)
Basic hand tools: drill, step bit, screwdriver, wrench

Step 1: Plan the routing

Before drilling anything, lay out where each line will run:

Tank vent: From tank top or filler neck, forward to the canister. Aim to rise to a high point near the canister.
Canister mounting: Upright, in the engine bay, away from exhaust heat.
Purge line: From the canister to a manifold vacuum source on the intake.
Atmospheric vent: Open port pointed down and forward.

Step 2: Vent the tank

If your tank has a factory vent fitting (most fuel-injected vehicles do), use it. If not, two common options:

Filler neck bulkhead barb: Drill a 3/8" hole in the filler neck above the highest fill point. Install a bulkhead barb with sealing washers. Tighten and check for fuel leaks.
Sending unit plate modification: With the tank out, weld or thread a fitting into the sending unit plate. Cleaner, more work.

Switching to a non-vented gas cap (or plugging the vent in your existing one) is the cleanest finish — the tank then vents only through your new line. Either approach works as long as the cap is no longer doing the venting.

Step 3: Run the vent line

Route fuel-rated vapor hose from the tank fitting forward to the engine bay:

Use P-clips every 18 inches or so to prevent chafing
Keep the line away from exhaust heat (or use a heat sleeve)
Rise to a high point near the canister — this acts as a liquid trap that helps prevent fuel from siphoning into the canister

Step 4: Mount the canister

Position the canister upright in the engine bay. Common spots:

Driver-side inner fender
Passenger-side inner fender
Firewall
Radiator support

Use the supplied bracket. Drill mounting holes carefully — check what is behind the metal before drilling.

Step 5: Connect the purge line

The purge port (usually labeled "P" or "PURGE") connects to a manifold vacuum source on the intake:

Carbureted: Tee into the PCV vacuum line, or into a direct manifold vacuum port on the carb base or intake plenum.
EFI without ECU purge control: Tee into a manifold vacuum source. Engine purges continuously while running.
EFI with ECU purge control: Use the factory purge solenoid (or add one) between canister and intake. Solenoid wires to the ECU EVAP output.

Note: Avoid ported vacuum (vacuum that only appears above idle) if you can. The canister will not purge at idle, charcoal saturates faster, and over time you can push liquid fuel through the system. Manifold vacuum is the cleaner choice on almost any build.

Step 6: Atmospheric vent

Point the atmospheric inlet downward and forward. A small inline filter on this port is worth adding to keep dust out of the charcoal — cheap insurance.

Step 7: Test

Fill the tank to 3/4. Verify no leaks at the new vent fitting.
Let the car sit overnight in a closed garage. The next morning the garage should smell like garage, not gas station.
Start the engine. Verify vacuum at the purge port (pinch test the line — engine should idle slightly cleaner with purge connected if charcoal is loaded).
Drive 20-30 miles. Park in the garage again. Check for fuel smell.

Troubleshooting

Still smells: Check the tank vent line for loose clamps or kinks. Verify the gas cap is non-vented.
Liquid fuel in the canister: Tank vent routing is too low. Add a high loop between tank and canister.
Rough idle after install: Purge line is connecting to ported vacuum, or the line is leaking air. Pinch test to isolate.
Charcoal smell from canister: Normal when new. Should fade in days.