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2G MFI/MPI Relay

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kahl23

15+ Year Contributor
1,093
12
May 10, 2004
Wellesley, Massachusetts
I know a lot of guys are trying to find the MFI/MPI relay, here's where it is and what it looks like on a 95 GSX.
 

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Solution
Testing the relay is a matter of applying power to the coil winding and making sure the contacts close. Inside the metal box are two relays, one for the MPI power and one for the fuel pump power. The fuel pump relay has two coil windings and energising either should close the contacts.

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This is the circuit for an 1G automatic car taken from the 1G tech manual. The manual cars have the starter relay and clutch safety switch replacing the AT Inhibitor switch for providing power to the second fuel pump coil to activate the pump while cranking the engine.

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Applying +12v to pin 10 and the ground (-battery) connection to pin 8 should make 12v show up at pins 4 and 5. Same deal for pin 3 and 7 causing...
That doesn't sound right. Sounds like you flipped over the connector and forgot to flop where pin 1 was when you did so. The Red with Black is the AC clutch. Pin 63 and 68 are black with blue stripe wires.

http://www.dsmlink.com/images/forums/1GECUPinout.pdf



That also doesn't sound right but it may be because there is a diode in series with the coil winding and you had it reverse biased. If the relay clicks when you put 12v across those pins and you read battery voltage at pins 4 and 5 while the battery is connected then the MPI side is good.

Your not going to see power at the MAF and CAS until you get the MPI relay switched on and you need to use the right wire.

once again, steve, your right. I was checking the wrong wires. The ECU has power coming to it but still no boot. Got it off craigslist so I'm ####ed out of $75 dollars. Damn. Well I learned a lot about car elec systems thanks so much. I hope this thread helps others in our position.
 
The ECU has power coming to it but still no boot. Got it off craigslist so I'm ####ed out of $75 dollars. Damn.

This doesn't surprise me. How many bad ECU's do you have now?
Pack them up and send them in. I'll fix you up.
 
I have two bad ones now. The first one is burnt halfway through the board. Idk why the other one doesn't work.

I just bought another one from the 1991, plugged it in and it fired right up. Opened it up and theres acid on the board!!! Its a curse


Is it possible that my car is burning them up??? I don't know what to do anymore...
 
I just bought another one from the 1991, plugged it in and it fired right up. Opened it up and theres acid on the board!!! Its a curse


Is it possible that my car is burning them up??? I don't know what to do anymore...

There are things in the car that can like a bad ISC but you have to remember that all of these ECUs have a problem with the caps leaking. Unless the caps have been changed before they leak or have been changed and the damaged repaired the are going to have problems.

My wife sometimes kids me and asked if I've fixed all of them yet but I've only made a dent.
 
Here are some pics of the burnt one.



Steve,
I am going to send you the one that works but is leaking. I rinsed the acid with isopropanol. The ecu causes clicking when its in the car.
 

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That's the +5v regulated filter capacitor and it looks like it leaked, shorted and blew up.
It's possible that in the process of doing so it spiked the CPU and interface chips. Look to telltale bubbles or cracks in the tops of the black square chips. The bigger is the CPU and the smaller interface logic. On EPROM ECUs there are two smaller square chips.

I don't believe that damage has anything to do with your car. It has to do with not getting the caps changed in time. It also doesn't have anything to do with the MPI relay except that a dead ECU may not turn the relay on.
 
I got a working one which I was refurbished. Now the car is making a screeching noise when I start it (starter?) and then it runs for awhile before it just suddenly dies. Do you think that is related to the ECU or something different. Thanks in advance

That's the +5v regulated filter capacitor and it looks like it leaked, shorted and blew up.
It's possible that in the process of doing so it spiked the CPU and interface chips. Look to telltale bubbles or cracks in the tops of the black square chips. The bigger is the CPU and the smaller interface logic. On EPROM ECUs there are two smaller square chips.

Can I send that one to you with my other two to look at? I bet you can fix the first two.
 
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I got a working one which I was refurbished. Now the car is making a screeching noise when I start it (starter?) and then it runs for awhile before it just suddenly dies. Do you think that is related to the ECU or something different. Thanks in advance

Can I send that one to you with my other two to look at? I bet you can fix the first two.

The screeching may be the alternator belt.

Not enough data to comment on why it dies.

Sure send them all in.
 
The screeching may be the alternator belt.

Not enough data to comment on why it dies.

Sure send them all in.

Steve,

It is not the sound of a belt screeching, its more like a grinding screech. Also today I noticed my MAF translator is stuck in red LED mode, which apparently is indicative of WOT+AUX.



UPDATE: I just went to start it this morning and it fired right up. Drove it to autopart store to get a CEL code but they didn't have OBDI, on the way home the CEL went off and the MAFT is back in green light mode. Strange.... maybe the switch just needed to warm up ?
 
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Testing the relay is a matter of applying power to the coil winding and making sure the contacts close. Inside the metal box are two relays, one for the MPI power and one for the fuel pump power. The fuel pump relay has two coil windings and energising either should close the contacts.

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in this picture can someone please point to where i need to apply power to..?? thank you very much
 
Here is what the MPI/MFI relays look like on a '97 GSX.

Same as the '95, only these are 2 separate relays and are behind that brace there, held on with the 2 bolts seen in the pic.

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The relay with red wires is for the ECU. That relay brings both pins 12 & 25 up to +12 on the ECU, with key on and the 30A 'moteur' in place. Which is located - fuse box in engine bay.

When that relay is activated, the ECU is in turn, activated. Once that happens, the ECU then turns on the OTHER relay next to it for a brief amount of time, which is for the fuel pump to pressurize (prime) the fuel system when the key is first cycled to the 'run' position.

So if you pull the 30A 'moteur' fuse in the engine bay, then neither of those relays will switch on = no fuel pump because = no ECU.

After wiring in a few things and fixing the ECU wiring, I wanted to throw this out there before I forgot :p

Any false info, please let me know and I'll edit :thumb:
 
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When that relay is activated, the ECU is in turn, activated. Once that happens, the ECU then turns on the OTHER relay next to it, which is for the fuel pump to pressurize (prime) the fuel system when the key is first cycled to the 'run' position.

Any false info, please let me know and I'll edit :thumb:
YES - false info: The fuel pump relay is only activated when the ECU receives CAS pulses (ie. engine is turning). This is true on all 1gs and turbo 2g's.

Also here's a pic of those 2 relays (on a 96-99) installed and from a different angle: http://www.dsmtuners.com/forums/attachment.php?attachmentid=90631&d=1230882598
 
hey guys, i am just about finished installing my 16g turbo and much more bolt ons on my 1996 talon tsi awd. i have a question about the mfi realy. i didnt run any oil through my lines or the turbo. my friend told me that i could disconnect the fuel relay and turn the car over to get oil through the lines without anything going wrong. is this true? also will it do the same for my water lines? how many turs do i have to do to get the oil and/or coolant through my lines safe enough to start my car? obviously i will plug the mfi relay back in before starting the car. i wouldnt ask on here if people around my place knew what a dsm was or could work on one (smh)

sorry if some info was wrong, but i know there is a realy (fuse) for the fuel pump. i just need to disconnect it. which fuse will i have to disconnect in order to put oil through all my lines without having the car starting? what is the realy called?
 
hey guys, i am just about finished installing my 16g turbo and much more bolt ons on my 1996 talon tsi awd. i have a question about the mfi realy. i didnt run any oil through my lines or the turbo. my friend told me that i could disconnect the fuel relay and turn the car over to get oil through the lines without anything going wrong. is this true? also will it do the same for my water lines? how many turs do i have to do to get the oil and/or coolant through my lines safe enough to start my car? obviously i will plug the mfi relay back in before starting the car. i wouldnt ask on here if people around my place knew what a dsm was or could work on one (smh)

sorry if some info was wrong, but i know there is a realy (fuse) for the fuel pump. i just need to disconnect it. which fuse will i have to disconnect in order to put oil through all my lines without having the car starting? what is the realy called?

http://www.dsmtuners.com/forums/newbie-forum/271826-how-prime-turbo.html

People do it all different ways, I would suggest just pulling the 20 amp engine/MPI fuse is the fuse box under the hood. It is easier than disconnecting the MPI relay. Then turn the engine over for 10 seconds a few times and you should be fine. You don't have to do this with your coolant like you asked. Remember to check for leaks!
 
alright thanks man. i spent a few more hours searching and someone mentioned that the crank angle sensor (CAS) is the best way to do it on a 2g. i know it is located somewhere around the fire wall. by unpluging the MPI fuse, will this eliminate all spark and cut fuel? i just dont want to see an engine with 2,500 miles go. also, will it throw and codes that i have to clear or restart the ecu? and thanks i was thinking 10 cranks and wait 10 seconds around 4 to 5 times. after i get enough oil pressure, would it be a good time to look for any leaks, or should i start the car and check?
 
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