Evo X Fuel Pump Relay Location: Complete Guide to Finding, Testing, and Replacing It
If you own a Mitsubishi Lancer Evolution X and are searching for the Evo X fuel pump relay location, here is the direct answer: the fuel pump relay is located in the engine bay fuse box, on the driver's side, near the firewall. It is a small, cube-shaped black relay typically labeled "FP" or "FUEL PUMP" on the fuse box cover diagram. However, this seemingly simple component has been the source of countless problems for Evo X owners, and knowing exactly where it is and how to deal with it can save you from expensive engine damage.
The Direct Answer: Where Is the Evo X Fuel Pump Relay?
The stock Evo X fuel pump relay sits inside the main fuse box under the hood. Open the hood and look at the fuse box on the driver's side, right behind the battery. Remove the plastic cover, and you will see a row of relays. The fuel pump relay is the one that controls voltage switching for the fuel pump. It is commonly a black relay, though some later models may have a blue or green one.
According to Road Race Engineering, the relay in question is specifically "in the fuse box under the hood". The common part number for the black relay is 8627A049, and the improved blue relay is MR400709. Do not confuse this with the cold start relay kit or the ACD relay, which are located elsewhere. The fuel pump relay is the one that handles the pump's high-current switching.
Why This Relay Matters More Than You Think
The fuel pump relay in the Evo X is not just a simple on-off switch. It is part of a dual-voltage system that the factory designed to extend fuel pump life. When the engine is idling or cruising, the pump runs at around 9 volts. Under boost or heavy load, the ECU sends a signal to the relay, and the pump gets full battery voltage of 13.5-14.5 volts. This switching happens every time you go in and out of boost, which is why the relay gets a workout.
Here is the catch: the factory black relays are notoriously unreliable. AMS Performance documented that the relay can get "stuck in the LOW position," meaning the pump never switches to high voltage. When that happens, the fuel pump cannot deliver enough fuel under boost, causing dangerously lean air-fuel ratios in the 13s or 14s instead of the safe 10s or 11s. That is a recipe for melted pistons and blown engines.
The Known Black Relay Problem: What to Watch For
Multiple performance shops have confirmed that the stock black fuel pump relay is a ticking time bomb. Road Race Engineering cut open failed relays and found that the internal contacts degrade over time. They reported that "all black relays are slowly eating themselves" due to arcing every time the relay clicks. The lever mechanism inside the relay does not apply enough pressure on the contacts, leading to high resistance, heat buildup, and eventual failure.
The worst part is that this degradation happens gradually. You may not notice any symptoms until the relay fails completely or starts causing intermittent issues. AMS Performance noted that they saw this problem repeatedly on tuning trips, where cars would suddenly go lean during baseline pulls. They would swap the fuel pump relay with the Daytime Running Light relay, and the problem would disappear immediately.
Symptoms of a Failing Fuel Pump Relay
Knowing the symptoms can help you catch a bad relay before it kills your engine. Here are the most common signs:
1. The engine stalls suddenly while driving. If the relay cuts power to the fuel pump, the engine dies without warning. Sometimes it restarts after a few minutes once the relay cools down, which is a classic sign of an intermittent fault.
2. Loss of power under acceleration. If you feel the car bog down or hesitate when you step on the gas, the pump may not be getting full voltage. The relay might still be working, but its corroded contacts are dropping voltage.
3. No fuel pump prime noise. When you turn the ignition to ON, you should hear a brief whirring sound from the rear of the car as the fuel pump primes. If you hear nothing, the relay is likely dead.
4. Hard starting or extended cranking. The engine cranks but takes longer than usual to fire up. This can indicate that the pump is not building pressure quickly enough because the relay is not delivering full power.
5. Check engine light with fuel system codes. Modern ECUs can detect low fuel pressure or circuit faults. Codes related to fuel pressure or pump circuit should prompt you to inspect the relay.
6. The car runs fine cold but acts up when hot. Heat can make a failing relay worse. If you notice problems after driving for a while, the relay may be thermal-sensitive.
How to Test Your Evo X Fuel Pump Relay
Testing the relay is straightforward and requires only a multimeter and a helper. Follow these steps:
Step 1: Locate the relay. Remove the engine bay fuse box cover. Refer to the diagram on the cover to find the fuel pump relay. It is usually one of the larger relays.
Step 2: Listen for operation. Have a helper turn the ignition key to ON (do not start the engine). You should hear the relay click and the fuel pump hum from the rear. If you hear a click but no pump noise, the relay contacts may be bad while the coil still works.
Step 3: Swap test. Find another relay in the fuse box that has the same part number and pin configuration. The Daytime Running Light relay or the horn relay are common candidates. Swap them and see if the problem moves. If the fuel pump starts working, the original relay is bad.
Step 4: Voltage test. With the relay removed, use your multimeter to check for 12V at the relay socket pins when the ignition is ON. You should have power on the coil supply pin and battery feed pin. If voltage is missing, you have a wiring or fuse issue.
Step 5: Continuity test. If you have a spare relay, you can test it manually. Apply 12V to the coil pins (85 and 86) and listen for a click. Use the multimeter to check for continuity between pins 30 and 87 when the relay is energized. If the contacts do not close, the relay is dead.
The Fix: Replace the Black Relay Immediately
Every reputable shop that works on Evo Xs recommends the same thing: replace the factory black relay with a higher-quality unit. Road Race Engineering states, "All Xs should have a blue or green relay installed ASAP. Stock or tuned. Especially if modded and not tuned!"
The upgraded relay is the Mitsubishi OEM blue relay (part number MR400709). It is a direct swap and costs around $20-30. You can find it at Mitsubishi dealers or online parts stores. Some owners also use the green relays from other Mitsubishi models, but the blue one is the most commonly recommended.
If you are running a high-flow fuel pump like a Walbro 255 or AEM 340, consider upgrading to a 30-amp relay. The stock relay is only rated for about 20 amps, and high-performance pumps draw more current. One Evo IX owner solved his fuel pump issues by installing "a higher amperage relay (30Amp) in the same location". This applies to the Evo X as well.
Step-by-Step Replacement Guide
Replacing the fuel pump relay is one of the easiest maintenance tasks you can do. Here is how to do it:
1. Disconnect the battery negative terminal. Safety first. Wait a few minutes for the ECU capacitors to discharge.
2. Open the engine bay fuse box. Press the tabs on the sides and lift the cover.
3. Identify the relay. Look for the black relay labeled for the fuel pump. If you are unsure, consult your owner's manual or the diagram on the fuse box cover.
4. Pull the relay straight out. It may require gentle wiggling. Do not pry with a screwdriver, as you can damage the socket.
5. Insert the new relay. Push it in firmly until it clicks into place. Make sure it is fully seated.
6. Reconnect the battery. Turn the ignition to ON and listen for the fuel pump prime. Start the engine and check for proper operation.
7. Keep the old relay as a spare. If you ever have a relay failure on a road trip, you can temporarily swap it with another relay to get home.
What About the Secondary Pump Relay?
Some Evo X owners add a secondary fuel pump for high-horsepower builds. If you have a surge tank setup or a second in-tank pump, the ECU can control it using the "Second Pump Patch" from TunerHelper. This patch uses the stock ECU to trigger a relay for the second pump based on engine load.
The wiring for the secondary pump relay usually goes to the ECU pin #51 or the passive wastegate solenoid wiring, depending on your setup. The intercooler sprayer light on the dash will illuminate when the second pump is active, giving you visual feedback. This is a popular mod for Evo X owners running E85 or big turbo setups.
Common Misconceptions About the Fuel Pump Relay
"I can test the relay by shaking it." Road Race Engineering debunked this: "Do not rely on the salt shaker test to see if you have a dead relay". The contacts can be badly worn without making any noise when shaken.
"The relay only fails in cold climates." AMS Performance and Road Race Engineering both saw failures in California, where it rarely freezes. The issue is not condensation, it is poor contact design and arcing wear.
"A bad relay will always throw a code." Not true. An intermittent relay may not trigger the check engine light, because the ECU sees voltage drops but may not register them as faults.
"The relay either works or it doesn't." Actually, it degrades slowly. You can have a relay that works fine at idle but fails under high load when maximum current is needed.
Prevention: Better Than Cure
The cheapest insurance for your Evo X engine is to replace the fuel pump relay before it fails. Here is a simple schedule:
- If your car has over 50,000 miles on the original black relay, replace it now.
- If you have upgraded your fuel pump to a higher-flow unit, replace the relay with a 30-amp version.
- If you track your car or drive it hard, replace the relay annually or every 20,000 miles.
- If you buy a used Evo X, replace the relay as part of your baseline maintenance.
The blue or green relays from Mitsubishi are much more durable. They use better contact materials and a more robust switching mechanism. The upgrade costs less than a tank of gas and could save you thousands in engine repairs.
Recommended Product: KEMSO Fuel Pump for Your Evo X
When it comes to replacing your fuel pump itself, not just the relay, you need a product you can trust. KEMSO offers high-performance fuel pumps that are designed as OEM replacements with lifetime warranty. Their pumps are built to handle the demands of both stock and modified Evo X engines, delivering consistent fuel pressure and flow under all conditions.
Whether you are upgrading to support a bigger turbo, running E85, or simply replacing a worn-out factory pump, KEMSO fuel pumps provide the reliability you need. The lifetime warranty means you only buy it once, and they stand behind their product for as long as you own your vehicle.
Visit their website to explore their full lineup of fuel pumps designed specifically for performance applications: https://www.kemsoracing.com/
Final Thoughts
The Evo X fuel pump relay location is in the engine bay fuse box, but the real takeaway is that you should not ignore it. This cheap, simple component is responsible for delivering consistent voltage to your fuel pump, and when it fails, the consequences can be catastrophic. Replace the black relay with a blue or high-amperage unit as soon as possible. Test it periodically if you drive your car hard. And if you are upgrading your fuel system, pair your new relay with a quality fuel pump from a trusted brand like KEMSO.
Your Evo X deserves reliable fuel delivery. Start with the relay, and you will sleep better knowing your engine is safe.
For more information on high-performance fuel pumps and fuel system components, visit https://www.kemsoracing.com/ and check out their latest offerings backed by a lifetime warranty.