The Eclipse MFI relay is a four pin relay found in the A-21x section of your Mitsubishi 3.0 liter engine bay fuse box. This part is primarily responsible for powering your fuel pump and enabling your Mitsubishi Eclipse to start. When this relay burns out your Mitsubishi Eclipse 3.0 liter V6 engine will not start, and your fuel pump will not turn on.
To check your fuel pump operation, insert your Eclipse ignition key and turn to the “ON” position. If you do not hear your fuel pump turning on, this could be a huge reason why your 3.0 liter Mitsubishi will not start.
Today I’ll be showing you how to test the MFI relay in your 2000 Eclipse with a 3.0 liter V6 engine, to correct any fuel pump issues with your Mitsubishi. Over time your MFI relay can fail, causing you serious starting issues or compromising your engine. When your MFI relay starts to fail, you may misdiagnose your crank angle sensor as being the problem.
As previously stated the Eclipse MFI relay is located in your fuse box near your driver side shock tower. This panel can be lifted off and you can access the MFI fuse through the fuse diagram below.
Once your cover is removed you can access the MFI relay. Check our Mitsubishi Eclipse fuse box diagram to the left to see where this relay is.
In order to complete this testing guide for your Eclipse MFI Relay, you will need a digital multimeter. You can also test this relay using an ohmmeter, and if you don’t know the difference check out our primer here.
When the Eclipse MFI relay in your Mitsubishi goes bad, the fuel pump and EFI system will not work properly. The part number for this relay is MR538851, and we’ll begin by checking the relay for continuity.
The first part of our test is to check for continuity between PIN 2 and PIN 3 of the Eclipse MFI relay. Turn the dial of your multimeter to read resistance Ω, and there should be approximately 70 Ω or continuity between these 2 pins.
Now construct wires and run the two wires from MFI relay terminal 2 to the positive battery terminal and terminal 3 to the negative battery terminal. At this point you will recheck for continuity. This time the posts to check are between the MFI relay terminals 1 and 4 while connecting and disconnecting the jumper wire at the negative battery terminal.
With the negative battery terminal disconnected PIN 1 and PIN 4 should return an open loop condition.
When you have the negative terminal of your battery connected, there should be less than 2 ohm Ω.
If the relay itself checks out, there’s some bad news in that the fusebox of your 3.0 liter Mitsubishi Eclipse may have some issues with the wiring.
The next part of the test will require you to check the A-18X connector with the MFI relay disconnected. Refer to our Eclipse MFI Relay wiring schematic below to match A to ! and B to 2 and C to 3 and so on.
Now measure the voltage at terminal A of the ENGINE harness or the fusebox itself.
There should be 12 volts of DC power at this pin. Now check the PIN B position for power, and this too should return 12 volts of battery voltage.
If the terminals at your A-18X terminal check out, and the Eclipse MFI relay checks out, there’s another cause for your Eclipse not starting.
If your Eclipse MFI relay returns values outside of this test, it’s a sign that this relay has gone dead. You will need to unplug this relay and install a new Eclipse fuel pump relay. Once you’ve reconnected a replacement Eclipse MFI relay, turn your key to the ON position to make sure your fuel pump is activated.
Have any questions about our fuel pump relay testing tutorial? Leave us a question below and let us know!