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Electrical Tech: Wiring, turbo timers, electronic boost controllers, gauges, fuses, wiring harnesses, wire tucks, car audio, and all other electrical component discussions.

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Old 02-21-2012, 08:20 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #1 (permalink)
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95 MPI Relay


I have a weird issue with my car starting and electrical drain.
I recently had a 6bolt swap done with Ecmlink 3.0 installed.
The guy who did the work claims the car will only start if the
MPI relay is grounded. He has two wires running from the
relay to the car's chassis not sure what pins but I can take pics no problem.
Now with that being said he also disabled my clutch safety switch.
If I leave my engine fuse in overnight the battery will drain
pretty significantly... Now this never happened before the swap,
if you read my other threads on this you will understand
the frustration the car had a starting problem due too the wrong cam.
Well my friend thought it was a electrical problem
and was testing wires from the ecu too the cas etc...
I need to know how too fix this "new problem"
I can't keep pulling this engine fuse all the time its becoming a pain in the ass.

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Old 02-24-2012, 05:44 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #2 (permalink)
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He's rigged it up to where the MPI relay is sent power thru those 2 wires he hooked into. I don't have a 95 wiring manual but, if someone knows or you can find out what Pin# at the ecu supplies power to the MPI relay then you can probably fix that issue yourself. Normally the ECU supplies the power to the MPI relay. Since you have an aftermarket ecu installed, you have had problems. You are going to need a wiring diagram and a volt meter to figure out why the ecu is not sending voltage to the MPI relay.

Then after you have corrected that problem, you will have to do a "draw test" or let the car sit overnight. See if the battery is weak/dead. If the battery is weak/dead then you will have to get a test light and perform a "draw test". Start pulling fuses until the "draw" goes out. Then, track down that circuit the fuse was pulled from and that will help you isolate what the cause of the "draw" could be on your battery. Start with pulling the starter fuse and alternator fuse first, those will have the largest amount of "draw" on the battery.
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Old 02-24-2012, 07:22 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #3 (permalink)
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The ECU doesn't send power to the MPI relay. It activates the relay to turn on the power to the ECU and the rest of the MPI circuit.

Which pins on the MPI relay did they ground? That will provide some clues as to what's broken.
It does sound like they have the MPI relay rigged up to leave the MPI powered all the time.

Last edited by steve; 04-25-2012 at 10:41 PM. Reason: spelling
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Old 02-24-2012, 08:12 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #4 (permalink)
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And rest of the MPI circuit and Starting circuit. Both of those circuits have to function properly. Dug this up. Hope this helps.

ecuwiringinformation [ECMTuning - wiki]
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Old 04-25-2012, 08:15 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #5 (permalink)
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Finally got a pic its actually only one wire that is grounded


Last edited by talon_42o; 04-25-2012 at 01:32 PM.
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Old 04-25-2012, 10:56 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #6 (permalink)
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It looks like pin 6 (blue/green stripe) is wired to ground. That would keep the MPI relay turned on all the time. That pin should go to pin 38 on the ecu.
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Old 04-26-2012, 06:21 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #7 (permalink)
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Now if I hook it back up too the wire in the harness and it doesn't start how would I go about finding the problem ?
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Old 04-26-2012, 01:06 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #8 (permalink)
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I happened to have an extra engine harness sitting next to me so I traced the wires out for you so there isnt any question as to where they go. Id bet that you have a stuck MFI relay. If replacing the relay doesnt work, PM me and Ill help you trace the problem.


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Old 04-26-2012, 09:29 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #9 (permalink)
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Quote:
Originally Posted by jdodds View Post
I happened to have an extra engine harness sitting next to me so I traced the wires out for you so there isnt any question as to where they go. Id bet that you have a stuck MFI relay. If replacing the relay doesnt work, PM me and Ill help you trace the problem.

The FSM pretty much says the same thing but makes it clearer what they are for.

Pins 5 and 6 are what the ECU uses to activate the fuel pump power (pin 5) and the MPI circuit power (pin 6). Like most things the ECU activates they are active low, the ECU pulls them to ground to turn them on. Since pin 6 is grounded that would cause the MPI power to be on all the time.

Usually this is one of three things. Someone blew the transistor that pulls ECU pin 38 to ground. The ECU isn't seeing the signal from the ignition switch that the car is in RUN or START position, or the backup power from the "room" circuit isn't reaching the ECU. I guess the wiring between the ECU and these things could also be suspect.

If ungrounding the pin causes the car not to start, the MPI relay isn't stuck.
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Old 04-28-2012, 08:17 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #10 (permalink)
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OK so should I inspect the ecu for damage? I know we messed with a bunch of wires at the power transistor and near the ecu... but the ecu would start in a 1997 tsi awd no problem so i'm doubting its the ecu.

Last edited by talon_42o; 04-28-2012 at 08:20 AM. Reason: forgot to add something
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Old 04-28-2012, 11:23 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #11 (permalink)
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You never know until you finish diagnosing. If the ECU works in another car I'd start checking to see if the wiring is good and if you see 12v at ECU pin 82 from the ignition switch when it's in RUN or START.

One way to check the wiring between the MPI relay and the ECU is to see if you see 12v at pin 38 when the the ignition is off. (after you fix the cut wire and hook the MPI relay back up to the ECU)
That should drop to 0v when you turn the ignition on and activate the MPI relay.
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Old 04-12-2013, 10:23 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #12 (permalink)
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Did you ever find out what was it? I have the same problem and it driving me nuts..
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Old 04-13-2013, 01:39 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #13 (permalink)
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Did you ever find out what was it? I have the same problem and it driving me nuts..
There is lots of diagnostic information in this thread, try using it and see if you can identify what's causing your problem.

You might be having the same symptoms but it remains to be seen if you have the same problem.
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Old 04-19-2013, 02:43 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #14 (permalink)
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Problem was my eprom ECU the whole time its triggering the ignition intermittently I now have a 1997 eclipse gsx and with that ECU same problem so I am sending it back too ECM link where they inspected it back in 2011.

MFI relay trigger is faulty on pin 38

Last edited by talon_42o; 04-20-2013 at 03:37 PM.
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