95 MPI Relay

Posted by talon_42o, Feb 21, 2012
Electrical Tech - Wiring, turbo timers, electronic boost controllers, gauges, fuses, wiring harnesses, wire tucks, car audio, and all other electrical component discussions.

  1. talon_42o

    talon_42o Proven Member

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    Essex, ON_Canada
    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.
    #1
  2. stars

    stars Proven Member

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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.
    #2
  3. steve

    steve DSM Wiseman

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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: Apr 26, 2012
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  4. stars

    stars Proven Member

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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]
    #4
  5. talon_42o

    talon_42o Proven Member

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    Finally got a pic its actually only one wire that is grounded

    [​IMG]
    Last edited: Apr 25, 2012
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  6. steve

    steve DSM Wiseman

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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.
    #6
  7. talon_42o

    talon_42o Proven Member

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    Essex, ON_Canada
    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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  8. jdodds

    jdodds Proven Member

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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.

    [​IMG]
    Last edited by a moderator: Jul 10, 2014
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  9. steve

    steve DSM Wiseman

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    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.
    #9
  10. talon_42o

    talon_42o Proven Member

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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: Apr 28, 2012
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  11. steve

    steve DSM Wiseman

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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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  12. suprasalas

    suprasalas Proven Member

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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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  13. steve

    steve DSM Wiseman

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    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.
    #13
  14. talon_42o

    talon_42o Proven Member

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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. LOL :hellyeah: :nono:

    MFI relay trigger is faulty on pin 38
    Last edited: Apr 20, 2013
    #14

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