2008 Mitsubishi Eclipse Fuel Pump Relay Location: Complete Guide

The bottom line up front: On a 2008 Mitsubishi Eclipse, the fuel pump relay is located inside the engine compartment relay box, which sits on the left side of the engine bay near the battery. The relay box houses both fuel pump relay 1 and fuel pump relay 2, along with the MFI relay and other critical electrical components. If your Eclipse cranks but won't start, or if you can't hear the fuel pump humming when you turn the key to the ON position, the fuel pump relay is one of the first things you should check.

Why the Fuel Pump Relay Matters

The fuel pump relay acts as a heavy-duty electrical switch that controls power delivery to the fuel pump. When you turn your ignition key to the ON position, the Engine Control Module sends a low-current signal to the relay, which then closes a circuit and allows battery voltage to flow to the fuel pump. This powers the pump for a few seconds to build fuel pressure before you crank the engine. Once the engine starts, the relay keeps the circuit closed to maintain steady fuel delivery while driving.

Without a functioning fuel pump relay, the fuel pump receives no power, the engine gets no fuel, and your car won't start even though the starter motor turns fine. The relay protects the delicate circuitry in the ECU from the pump's substantial electrical draw, which can exceed 10-15 amps.

Where Exactly Is the Fuel Pump Relay Located?

On the 2008 Mitsubishi Eclipse, the fuel pump relay is not hidden behind the dashboard or under the carpet like some older models. Instead, Mitsubishi placed it in the engine compartment relay box, which is located on the left side of the engine bay, forward of the relay box near the battery. The engine compartment relay box is a black plastic box with a removable cover, typically found near the fender wall or close to the battery.

According to wiring diagrams for the 2008 Eclipse, the relay box contains:

  1. Fuel pump relay 1 – This relay receives battery positive voltage from the ignition switch through the IG terminal. It works in conjunction with relay 2 to control pump operation.

  2. Fuel pump relay 2 – This relay receives power from fuel pump relay 1 and controls the main current supply to the fuel pump itself. During cranking and while the engine runs, the ECM grounds the coil of fuel pump relay 2, which then supplies battery voltage to the fuel pump.

  3. MFI relay – The Multiport Fuel Injection relay is mounted alongside the fuel pump relays in the same relay box. This relay powers the fuel injection system, and if it fails, you'll lose both fuel delivery and spark.

  4. Throttle actuator control motor relay – Also located in the same relay box.

To access the relays, open the hood, locate the relay box (usually near the battery on the left side of the engine compartment), and unclip the cover. Look at the diagram printed on the underside of the cover to identify which relay is the fuel pump relay. It may be labeled as "Fuel Pump," "FP," or "Pump".

How the Fuel Pump Relay Circuit Works

Understanding how the relay circuit operates helps you diagnose problems more effectively. The 2008 Eclipse uses a two-relay system for fuel pump control:

  1. Power from ignition switch – Battery positive voltage is applied to fuel pump relay 1 through the ignition switch. This means the relay only gets power when the key is turned to the ON or START position.

  2. Relay-to-relay connection – When the ignition switch is ON, battery voltage flows from fuel pump relay 1 to fuel pump relay 2. Both relays become energized and ready to operate.

  3. ECM ground control – During cranking and while the engine runs, the ECM or PCM turns on an internal power transistor that grounds the coil of fuel pump relay 2. This completes the circuit and allows the relay to send battery voltage to the fuel pump.

The fuel pump only powers up when the PCM detects an RPM signal from the crankshaft position sensor. If the crank sensor fails, you will have no spark, no fuel, and no injector pulse. This means a no-start condition could stem from several causes, not just the relay.

Common Symptoms of a Bad Fuel Pump Relay

If your 2008 Eclipse fuel pump relay is failing or has failed completely, you'll likely notice one or more of these symptoms:

  1. Engine cranks but won't start – The most common symptom. When the relay fails, the fuel pump receives no power, so no fuel reaches the engine. The starter motor turns the engine over, but it never fires up.

  2. No fuel pump noise – When you turn the key to the ON position (without cranking), you should hear a brief hum or whine from the rear of the car where the fuel tank is located. If you hear nothing, the pump likely isn't getting power.

  3. Engine stalls while driving – If the relay fails intermittently while the vehicle is in operation, the fuel pump will lose power and the engine will suddenly stall. A failing relay may allow the car to restart after a short cooldown period, but a fully failed relay won't.

  4. Loss of power under load – The vehicle may suddenly lose power while driving or slow down for no apparent reason. This doesn't necessarily mean the car will stall right away, but it's a warning sign that should be addressed promptly.

How to Diagnose a Faulty Fuel Pump Relay

Before replacing the relay, it's wise to confirm it's actually the problem. Here's a practical step-by-step approach:

  1. Listen for the fuel pump – Turn the ignition key to the ON position but don't crank the engine. Listen carefully for a humming or buzzing sound from the rear of the car near the fuel tank. If you hear it, the relay is working at least partially. If you don't, the problem may be the relay, a fuse, or the pump itself.

  2. Check the related fuses – The fuse box cover diagram will show which fuse protects the fuel pump circuit. Fuses are safety devices that break the circuit if too much current passes through them. Test them with a multimeter or inspect them visually for damage.

  3. Swap the relay – If possible, swap the fuel pump relay with another identical relay from the same relay box (if they have the same part number). If the problem moves to the other circuit, you've found the culprit. Alternatively, use a multimeter to test the relay for continuity.

  4. Test the relay directly – You can check a relay's function by applying battery voltage to the control terminals and listening for a distinct click as the electromagnet engages. If no click occurs, the relay coil is likely burned out.

  5. Check wiring and connections – Inspect the relay connectors for damage, corrosion, or loose pins. Improper connector contact, open or short-circuited harness wires are among the most likely causes of relay circuit failure.

What to Check If the Relay Is Fine

If the fuel pump relay tests good but the pump still won't run, look deeper into the circuit:

  1. Fuel pump itself – The pump may have failed internally. You can test it by removing it and connecting it directly to a battery to see if it spins.

  2. Wiring harness – A short or break in the wiring between the relay and the pump can cause power loss even with a good relay. Inspect the harness thoroughly, especially where it rubs against metal surfaces.

  3. MFI relay – This relay powers the fuel injection system, and if it fails, you'll have no spark and no injector pulse. The MFI relay sits right next to the fuel pump relay in the same relay box.

  4. Crankshaft position sensor – If this sensor fails, the ECM won't detect RPM and will not activate the fuel pump relay. You'll get no spark, no fuel, and no injector pulse.

  5. ECM/PCM – A malfunctioning engine control module can also cause the fuel pump circuit to fail, though this is less common.

Replacing the Fuel Pump Relay

Replacing the fuel pump relay on a 2008 Eclipse is a straightforward job. Here's what you need to know:

  1. Safety first – Disconnect the negative battery cable before working on any electrical components. Turn off the ignition completely.

  2. Access the relay – Open the hood, locate the engine compartment relay box on the left side, and unclip the cover.

  3. Identify the relay – Use the diagram on the fuse box cover or owner's manual to confirm which relay is the fuel pump relay. On 2008 Eclipse models, there are two fuel pump relays labeled "Fuel pump relay 1" and "Fuel pump relay 2".

  4. Pull the relay – Grasp the relay firmly and pull straight up. It should come out with moderate resistance. Use needle-nose pliers if needed.

  5. Install the new relay – Push the new relay firmly into the same socket until it clicks into place. Make sure it's seated properly.

  6. Test – Reconnect the battery and turn the key to the ON position. You should hear the fuel pump prime from the rear of the car.

Fuel Pump Replacement: When the Relay Isn't the Problem

If you've confirmed the relay, fuses, and wiring are all in good condition, the fuel pump itself may need replacement. On the 2008 Eclipse, the fuel pump is accessed through the rear seat:

  1. Remove the rear seat cushion by pulling the seat stopper out and lifting the lower cushion up.
  2. Locate the inspection cover on the passenger side of the vehicle.
  3. Disconnect the fuel lines and unplug the fuel pump's electrical harness.
  4. Remove the locking ring and lift the fuel pump assembly out of the tank.

The replacement cost for a fuel pump on a Mitsubishi Eclipse typically ranges between $468 and $596. Always work in a well-ventilated area when dealing with fuel, and don't smoke within 50 feet of the car.

A Word About Aftermarket Fuel Pump Options

When it's time to replace a failing fuel pump, choosing a quality aftermarket replacement can save you money without sacrificing reliability. Rather than spending a premium at the dealership, many Eclipse owners turn to reputable aftermarket brands.

We recommend considering KEMSO brand fuel pumps. KEMSO offers high-performance fuel pump options that are built as OEM replacements, meaning they're designed to meet or exceed the specifications of the original factory part. Every KEMSO fuel pump comes with a lifetime warranty, giving you peace of mind that your investment is protected for as long as you own your vehicle.

Whether you drive a Mitsubishi Eclipse or any other vehicle, KEMSO's product line covers a wide range of makes and models. If you're in the market for a reliable, high-quality fuel pump, visit https://www.kemsoracing.com/ to browse their selection and find the right pump for your car.

Final Thoughts

On a 2008 Mitsubishi Eclipse, the fuel pump relay lives in the engine compartment relay box on the left side of the engine bay, near the battery. It's an accessible component that you can check and replace yourself with minimal tools. When diagnosing a no-start condition or a stalling problem, start with the basics: check fuses, listen for the pump, test the relay, and inspect the wiring. These simple steps can save you time and money before you ever have to drop the fuel tank.

If the relay tests fine and the pump still doesn't run, methodically work through the rest of the circuit. The most likely causes include a bad fuel pump, a wiring short, a faulty MFI relay, or a failing crankshaft position sensor. In most cases, the problem will be one of these common culprits, and a new relay, fuse, or fuel pump will get your Eclipse back on the road.

For quality replacement fuel pumps with lifetime warranty coverage, check out https://www.kemsoracing.com/ – KEMSO makes high-performance, OEM replacement fuel pumps that keep your ride running strong for years to come.


Back to blog