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Resolved no spark, no CEL

Posted by sacrileger, Jun 18, 2019

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  1. sacrileger

    sacrileger Proven Member

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    Very odd situation... I drove the car last summer, parked it for the winter, wanted to drive it this summer, tried to start it just now,... no spark. Started tracing the problem. Noticed my CEL was not ON. Accessed resources you guys graciously provided over the years here. Found this post: 1G basic ECU MPI circuit function ... Started tracing the problem as per instructions:
    1. checked two fusible links on the battery terminal and 10Amp room fuse #19 :cool:
    2. checked for battery voltage at ECU backup power pin #103 and MPI relay pin #10 :cool:
    3. Measured ground continuity to ECU pins #106 (dont have #101) and MPI #6 :cool:
    4. Couldnt get voltage on ECU pin #102, #107 even when cranking :notgood:
    5. Shorted MPI pin #8 (el.harness) and got no voltage on pin #4 or #5
    questions:
    1. what are the possible mistakes i made in measuring voltage on ECU pin # 102 and #107 and MPI pin #4 and #5 ?
    2. if i am correct and not getting power on those ^^^ four pins, what is my next step?
    Edit #1: in this link: No power to ECU.. . is step #2 assuming the engine is cranking when the key is in the RUN position (clutch pushed in)?

    Edit #2: answering my question^^^, it would appear that when the key is in the ON position, there is continuity on ignition switch 6, 3, 4, 2 (so there should be power going to ECU pin #102, and #107)
    DSCF0357.JPG
     
    Last edited: Jun 19, 2019
  2. dustyboner

    dustyboner DSM Wiseman

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    If you have power to pin 10 on the relay and you ground pin 8 but don't get voltage at pin 4 and pin 5, your relay is bad.
    Did you hear it click when you grounded pin 8?

    upload_2019-6-18_23-19-31.png
     
  3. kenuwine4g63

    kenuwine4g63 Proven Member

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    Does your fuel pump turn on? Check your transistor.
     
    kenuwine4g63

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    1995 Mitsubishi Eclipse GST
    000.0 whp · 000.0 lb/ft · 2G DSM
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  4. sacrileger

    sacrileger Proven Member

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    I heard a click when the relay was connected to the harness and i turned the key ON. However, for my test, i disconnected the relay, shorted pin #8 at the harness by running a wire from the harness pin #8 to the ground and expected to get voltage on harness connector pin #4 and #5... which i did not get.
     
  5. sacrileger

    sacrileger Proven Member

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    yes... i did that before i noticed the CEL was not ON. The fuel pump works; however, the PTU gave me funny readings. I will re-check PTU once i get the CEL back ON.
     
  6. steve

    steve DSM Wiseman

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    The MPI relay would have to be connected to the harness to do the switching of power from pin 10 to pins 4 and 5.

    The ECU can be disconnected while your testing the MPI relay since you going to ground pin 8 yourself. (instead of the ECU doing so when it sees pin 110 go high)

    Pins 101 and 106 are connected together internally but all the harnesses I've seen still had a black wire to both pins.

    ECU pin 110 only tells the ECU if the ignition switch is turned on or off. ECU pin 108 is used to sense that the switch is in the START position and your trying to start the engine.

    When the ECU sees pin 110 go high, it pulls ECU pins 63 and 66 to ground. These are connected to MPI relay pin 8 and should cause the relay to switch the power coming in on it's pin 10 to it's pins 4 and 5 which run the the ECU pins 102 and 107. There is no direct connections between the ignition switch and the ECU power pins. Grounding pin 8 on the MPI relay duplicates the ECU pulling it low and should cause it to activate. As Dustyboner said, if it doesn't and you have power to pin 10 the relay is bad. (It's a common fault from capacitors leaking to lose the internal connection to pins 63 & 66)
     
    Last edited: Jun 19, 2019

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    1991 Mitsubishi Eclipse GSX
    manual · 1G DSM
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  7. sacrileger

    sacrileger Proven Member

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    I am trying to make sure i am getting power leading to the MPI relay so perhaps i am confusing pins on the relay with female pins on the connector. I am following the manual which numbers the sockets for pins in the connector like this:
    DSCF0359.JPG

    so following the diagram ^^^, i grounded the connector socket/pin #8 on the harness and with the key in ON position i observed power on the connector socket/pin #3 and #10 and nowhere else. That is the actual power that would go into the MPI relay if it was connected. Would that be correct to get the power configuration as stated?
    p.s... i will bench test the MPI relay to make sure it works if i am getting power on correct pins.
     
    Last edited: Jun 19, 2019
  8. steve

    steve DSM Wiseman

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    That looks like they are showing number as if you grabbed the end of the connector and looked at it with the wires facing away from you, which is flopped from the way the factory manuals show them.

    The Mitsubishi and Chrysler FSM show the connector pin outs with the wires facing you or looking down into the female connector with the male pins sticking up. Left to right and top to bottom the pins are:
    1 2 3 4 5
    6 7 8 9 10
    As shown in https://www.dsmtuners.com/threads/1g-basic-ecu-mpi-circuit-function.435961

    From the 90 FSM the MPI relay wires are colored
    1 Not Connected
    2 Black w/White stripe
    3 Black w/White stripe
    4 Red
    5 Red
    6 Black
    7 White w/Red stripe
    8 Black w/Blue stripe
    9 Black w/Yellow stripe
    10 Black w/Red stripe

    To test you either need the MPI Relay plugged in or you need to apply 12v to pin 10 and then ground 8 on the relay not the harness. Then the relay pins 4 and 5 will be hot with +12v
     
    Last edited: Jun 19, 2019

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    1991 Mitsubishi Eclipse GSX
    manual · 1G DSM
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  9. dustyboner

    dustyboner DSM Wiseman

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    upload_2019-6-19_21-2-2.png
     
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  10. sacrileger

    sacrileger Proven Member

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    yes, my manual shows the pin outs flopped which just adds to the confusion when comparing with some posts on here... but all good

    thanks for including the wire color markings. the only wire that is different is #2. instead of black with white stripe, i have black with green stripe... but that's because i swapped the harness to accommodate the switch from 4g37 to 4g63. here's the post from last year:
    rewire 4G63 el. connectors to fit 4G37 connectors

    i bench tested the MPI relay as per @dustyboner instructions...it checks out. i will be proceeding with your earlier post to check what's going on with pins at the ECU.
    btw, i edited the title to this post to "no spark, no CEL" as that appears to be the root of my problem, not MPI pins #4 and #5 which i misdiagnosed.
     
  11. sacrileger

    sacrileger Proven Member

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    thank you, this was helpful and clear. the MPI relay checks out. this schema also answers my earlier question if i should see power coming from the harness to pin #3 on the MPI relay. I see power on the harness going to MPI pin #3 when the ignition key is in ON position, in addition to power going to MPI pin #10, ... which corresponds to the last test where where pin #7 is grounded and #3 is energized.

    btw, i edited the title to this post to "no spark, no CEL" as that appears to be the root of my problem, not MPI pins #4 and #5 which i misdiagnosed.
     
    Last edited: Jun 20, 2019
  12. sacrileger

    sacrileger Proven Member

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    What is the voltage on ECU pin #110 w/ key at ON? I expected 12V since it likely comes from ignition switch #4 (see diagram in first post above). But only got 9V. I might be dealing with a bunch of problems at the same time here. I checked voltage that go to fuses in position #11, 12, 18, and 19. You already know which ones they are but here is the layout for somebody who might wonder later...
    fusebox.jpg
    this is how these fuses are labelled on my cover
    DSCF0356.JPG

    and this is what these fuses protect:
    fusebox-diagram.jpg

    anyways, my battery is not new but it was charged for this test. the output at the battery was 12V.
    I checked fuse #19 and got almost 12V.
    With the key in ON position, these are the readings I got:

    #11 - 12V
    #12 - 9V
    #18 - 1V .. yes, one volt.

    so my two questions are...
    1. Is it correct to expect 9V on fuse #12 and 1V on fuse #18?
    2. Does the ECU pin #110 w/ key at ON expect 12V or 9V?

    Needless to say, I dont want to jump too far ahead until the testing is completed; however, I looked inside the ECU and observed some corrosion and what appears to be dried out solution. The ECU might be faulty... but I want to make sure the voltage going to the ECU is correct before i start sourcing out new/refurbished ECU:

    DSCF0374.JPG
     
  13. steve

    steve DSM Wiseman

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    Lets address the easy part first.

    Yes, your capacitors are leaking. The cracking of the conformal coating is one sign and you can see the corrosion of the copper circuit traces around the edges of the SMD capacitors around the larger electrolytic all the way over to the cap for the A2D by the CPU. You can also see the corrosion halo around the ground via above C14.

    That ECU needs attention now.

    You asked what voltage should you see at ECU pin 110 when the ignition switch is on. It should be battery voltage. So assuming the starter wasn't running 12v would be reasonable. When the starter motor is running it's not unusual for the electrical system voltage to drop to 9v.

    If you're seeing 9v with just the ignition switch in the run position I'd disconnect the ECU and check again to make sure it's not pulling the voltage down and start working backward to see where things are failing. Many other things get powered in that position and any of them could be pulling the voltage down.

    1v @ Fuse #18 is a problem. I assume you checked that several times and verified by seeing if the dome light works. (it wouldn't if you only have 1v there)
     

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  14. sacrileger

    sacrileger Proven Member

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    it looks like i am good with getting 12V on all four fuses #11, 12, 18, 19 now.

    I checked out the FSM dealing w/ electrical issues,
    https://drive.google.com/file/d/1UKettrv_AVM2eg1-lNQdtDt3ojCxIr8k/view

    i looked up where all the grounding points are, sanded all down, cleaned up the door light switch on the rocker panel which turns on/off the dome light and it all came alive.
    i get 12V (~11.5V) on ECU pin #103 and #110 so i can proceed with the rest of the ECU test.
     
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  15. steve

    steve DSM Wiseman

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    Good work!
     

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  16. sacrileger

    sacrileger Proven Member

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    I wonder if you meant "the ECU is bad" rather than "the RELAY is bad" in the second last sentence above...?

    I am struggling with the terminology here: you said above: "When the ECU sees pin 110 go high, it pulls ECU pins 63 and 66 to ground..."
    Does it mean i should see voltage coming out of the ECU pins 63 and 66? Or not? I checked and i get no voltage coming out of the ECU on any pins other than 102 and 107.

    Also, i am curious what this means and what happens internally:
    1) when the ECU is NOT connected to the harness, I see voltage on the plug/connector leading to the ECU pins #56, 63, 64, and 66.

    2) when the ECU is connected to the harness via plug/connector with receptacles for pins #101 to 110, I get voltage on the plug/connector leading to the ECU pins #56, 63, 64 but no power on #66. I am guessing voltage from ECU pin #102 or 107 turns something off upstream.

    Where ... or what exactly cuts the power off to wires leading to ECU pin #66 ?? What does it mean?
     
  17. dustyboner

    dustyboner DSM Wiseman

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    upload_2019-6-22_18-0-39.png upload_2019-6-22_18-1-4.png
     
  18. steve

    steve DSM Wiseman

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    We were talking about testing the MPI relay by itself per the procedure dustyboner posted.

    There is no voltage being sourced by the ECU here, the voltage is being sourced by the battery via the MPI fuse and passes through the coil inside the MPI relay and is switched to ground by the ECU or not depending on the ECU sensing battery voltage on ECU pin 110. The transistor inside the ECU on pins 63 and 66 completes the circuit and causes current to flow. Because the coil has resistance there is a voltage drop across it when current is flowing. When the ECU isn't switching the relay on there is no current flowing and the voltage on both ends of the coil is the same.

    ECU pin 56 connects to one of the relay coils for activating the Fuel Pump in the MPI relay. How the voltage gets presented at the ECU pin works the same way except it's connected to and sourced from the Ignition circuit.

    ECU pin 64 connects to the Check Engine Light
    ECU pins 63 and 66 connects to the relay coil for activating the MPI circuit like described. I can't say why you see one thing on 63 and another on 66 off hand. The wiring diagrams show both pins being connected to pin 8 on the MPI relay. You can confirm that with your meter by measuring the continuity of the wiring with both the MPI relay and ECU disconnected. Both wires should be black.
     
    Last edited: Jun 22, 2019

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  19. sacrileger

    sacrileger Proven Member

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    With everything connected, MPI and ECU, ignition key in ON positions and then manually grounding pin #8 on the MPI relay, the MPI relay activates (clicks) and turns the CEL ... ON.

    Is this the final proof the ECU pin # 63 and/or 66 is the culprit? Or is further testing needed to figure out which pin on the ECU is the problematic one?
     
  20. steve

    steve DSM Wiseman

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    That would tend to point at either corrosion damage to the circuit traces or a blown transistor for the relay coil inside the ECU. I've seen both types of failure and sometimes at the same time. To clarify, the trace from pin 110 to the internal circuits sensing it's state, or the trace from the transistor that grounds pins 63 /66, or a blown transistor can each cause this behavior.

    This would be where the factory service diagnostic tree would say replace the faulty ECU.
     

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