Fuel Rail Kit Installation for 9th Gen Civic Si

By ACUITY Instruments: Performance Automotive Products | Published: 2026-10-25

Category: How-to Guides

Step-by-step guide to installing a fuel rail kit on a 9th Gen Honda Civic Si using the OEM fuel line. Avoid common mistakes and upgrade your fuel system.

Quick answer

Installing a fuel rail kit on a 9th Gen Civic Si is a straightforward upgrade that cleans up underhood appearance and simplifies future fuel system modifications. Use the stock fuel line and choose gauge placement before you start.

Why upgrade the fuel rail?

The factory fuel rail works fine for a stock car, but it can become a bottleneck if you plan to add a larger fuel pump, injectors, or a pressure regulator later. An aftermarket fuel rail like the ACUITY kit gives you a clean mounting point for a fuel pressure gauge and makes it easier to service the fuel system without removing the whole rail.

Trade-offs to consider

This kit is designed to work with the OEM fuel line, so you won't need to buy a custom line. However, you must decide upfront whether you want a fuel pressure gauge and where to mount it—top or side. The gauge is not included, so order one separately if you want real-time pressure readings. Also, the kit does not include a new fuel line; reuse your stock one.

Installation steps

Depressurize the fuel system: Remove the fuel pump fuse or relay, then start the engine and let it run until it stalls. Turn the key off. This prevents fuel spray when you disconnect the lines. Skipping this step can lead to a dangerous fuel spray. Always verify the system has no pressure by opening the fuel fill cap and listening for a hiss.
Disconnect the battery negative terminal: Use a 10mm wrench to remove the negative battery cable and tuck it away from the terminal. This eliminates the risk of sparks near fuel vapors. Even with the system depressurized, a spark could ignite residual fumes. Never skip this safety step.
Remove the factory fuel rail: Unbolt the two 10mm bolts holding the factory rail to the intake manifold. Carefully lift the rail straight up to avoid bending the injectors. Disconnect the fuel line quick-disconnect by pressing the release tab. Injectors are fragile. If they stick, gently rock the rail side-to-side—do not pry against the injector body.
Assemble the new fuel rail kit: Install the supplied fittings into the new rail. Decide now if you want a fuel pressure gauge and on which port (top or side). If you're not using a gauge, install the plug provided. Torque fittings to manufacturer spec (typically 20-25 ft-lb). Choosing gauge placement after assembly means disassembly and rework. Decide before you tighten anything.
Connect the OEM fuel line: Press the stock fuel line quick-disconnect onto the rail's inlet fitting until it clicks. Give it a gentle tug to confirm it's locked. Route the line away from hot or moving parts. The quick-disconnect can feel seated when it's not. Always test with a tug to avoid a fuel leak under pressure.
Mount the new rail and reconnect battery: Set the rail onto the injectors and press down evenly until all injectors seat. Reinstall the two 10mm bolts and torque to 7-10 ft-lb. Reconnect the battery terminal. Uneven seating can cause an injector O-ring to roll, leading to a vacuum leak or fuel leak. Check each injector visually.
Prime the fuel system and check for leaks: Turn the key to ON (but do not start) for 3 seconds, then OFF. Repeat 3-4 times to build pressure. Inspect all fittings and the quick-disconnect for drips. Start the engine and recheck while running. A small leak may only appear under running pressure. Keep a rag handy and shut off immediately if you see fuel.

Product details

Fuel Rail Kit for the 9th Gen Civic Si Using the OEM Fuel Line: This kit is designed for the 9th generation Honda Civic Si and is intended to be used with the stock fuel line. You save money by reusing the existing line, but you must verify your stock line is in good condition before installation.
Fuel Rail Kit for the 9th Gen Civic Si Using the OEM Fuel Line