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.
To access your Mitsubishi MFI relay, open your fuse box by undoing the locking tabs on your fuse cover.
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 pins shown in our Mitsubishi fuel pump relay diagram are signified by the dot when you flip the relay over.
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.
You will be checking the A-18X connector or the fusebox for this part of the test. Turn the dial of your multimeter to read DC voltage and turn your Eclipse ignition to the “ON” position.
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!
I appreciated how you explained the relay test. I only have one question and I am not trying to make a foolish issue, but, I am sure you meant Refer to our Eclipse MFI Relay wiring schematic below to match A to 1 instead of !.
Hi Jack, thanks for reading our MFI relay test guide. You are correct sir! sorry about that confusion but glad it wasn’t too hard to figure out. Much appreciated sir!
Yeah that great!! Thanks!!
What does it mean if the relay a18 X you jump The Wire some the red and white to the red I believe it would be pin 1 and 3 on the harness side and your car works it starts and runs but without it it does not run?
Hi Ray, thanks for reading
What year is your Eclipse and what are the issues you are having? Does the vehicle respond once you turn the key to the ON position? Does your MFI relay click at all? Let me know and I can try to help! Thanks
Would this be the same for an Evo 8 B-19X relay?
Sorry Joe but no, the 2 MFI relays are not the same. Sorry about that
I have a 2003 eclipse and I am having issues starting the car started running hot at a light and less than a quarter mile up the road it shut off. Found out the timing belt snapped. Fixed that issue but she still only cranks over but no start. I replaced the fuel pump relay and the fuel pump. Please help
Hi Josh, if you own a 2003 Mitsubishi it’s, unfortunately, an interference type engine, which means that if your timing belt snapped, things collided inside your engine. I would go buy or rent a cheap compression checker, and see if you have compression in your engine.I’m willing to bet that you bent a valve when your timing belt snapped, which will ruin your engine.
Sorry to be the bearer of bad news. Let me know how it turns out. thanks for commenting
Will have to do that. So just so I understand properly. Would the engine still turn over with a bad valve? How expensive you it be to just to replace the valves?
yes.. the engine can in theory still turn over and crank with a bent valve. THe problem is your cylinder isnt sealing anymore, which eliminates the possibility of any combustion or the engine starting.
Just replacing a valve is rarely enough, you will need some sort of valve job not to mention the timing belt job that must be completed as the cylinder head has to be removed.
I have 2002 eclipse 2.4l that cranks but wont start. KOEO no check engine light. Checked mfi relay. It is good. Put jumper wire across terminals for load side of relay. Now check engine light comes on and car will start. Check of the terminals for control side of relay found power coming into relay but no ground from the other terminal. Where does the mfi relay get its ground to activate the relay when the key is turned on.
Hi Kevin, sounds like your MFI relay is the main problem.
I would circle back or add grounds to your ECU harness, or conversely ground the MFI relay directly to see what will happen. If you add ground and it starts normally, sounds like you have a broken wire somewhere.
Best of luck!
Hey great info but i got a 2006 eclipse turn ovee but dont crank is not gettin pluse on the injector nether in the coils already change the crank and cam sensor but still nothing check the coil harness got power and ground but not the pulse im getting frustrated with this car any suggestions
Hey Freddy, sounds like you’ve got a bad Eclipse starting problem there.
Have you recently changed / modified the car at all? Is this a new engine? If you have already checked the eclipse cam sensor and crank sensor, have you already checked your ECU? If you are saying there’s no pulse or spark, I would suggest checking the ECU first given you have done all the pre-requisite work. This includes but is not limited to checking the wiring on your crank sensor and ECU wiring.
Hope that helps!
I have a question concerning this test what if you get voltage with the key off position but when you turn key on the voltage goes away,also if I use a single hot wire to check fuel pump without using a suplimental ground will the pump come on so that I can see that it is working if not what progs do I connect hot and neg to at plug to check fuel pump?
Hi Ace, thanks for reading.
Okay, really quickly just wanted to ask. Did you mean that the key in the OFF position returns a voltage? And when you turn the Eclipse key to ON you get nothing?
Do you hear the Eclipse relay kick on when you turn the key to the ON position?
I have an ’03 Lancer with a crank, no start condition. I recently replaced the two fuel pump relays because they showed too much resistance (About 130, when they were supposed to be approximately 70 like the Eclipse’s MFI). The new ones I bought tested in the low hundreds for resistance. Are they unusable? This guy from “Watches and Wrenches” on YouTube said that relays should measure between 50 & 120, but the service manual says they should be around 70.
Hi DJ, okay that’s a weird issue. You bought new ones and they are out of spec already?
can you describe your no start issue further?
I have a 2002 mitsubishi eclipse automatic My cranks runs for about 10 minutes and then it dies
I wait for about 20 minutes then it’s able to start again
I also just replaced the fuel pump and relay
But same issue
What do you think the problem is?
Hey Jesus, thanks for reading.
so it sounds initially like a fuel pressure issue. Can you check your pressure at your rail with the key to the “ON” position? Should be static and around 30-40 PSI.
Hope that helps