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  1. #11
    Join Date
    Aug 2020
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    Middle Tennessee
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    Do you have spark?
    2020 Supra SA

  2. #12

    Default No fuel pump power

    Quote Originally Posted by Probably the Killswitch View Post
    I am holding my multimeter leads to the connections on the pump while someone else cranks the key. No voltage at any point.
    I have a service/ diagnostic manual for the MEFI 4 system. In it, it states that when the key is first turned on you should have fuel pump run 2 seconds. The ECM sends a signal directly to the fuel pump relay and then after 2 seconds it does not receive an ignition signal it shuts power to the fuel pump relay. I wouldnt think that coolant temp sensor or oil pressure sensor would be in that initial 2 second circuit.
    I would recheck the fuel pump relay fuse and the relay.

  3. #13
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    Mar 2021
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    South Georgia
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    Is there by chance another fuse holder that was added anywhere in the circuit? Really does sound like it would end up being something simple like that by how you described it suddenly not working. Of course I guess a failure in the control module could also just suddenly happen too. Double check to make sure it's not a loose connection or corrosion in a fuse holder prior to it reaching the pump. See if there is voltage on either side.

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  4. #14

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    Quote Originally Posted by secondsupra2004 View Post
    I have a service/ diagnostic manual for the MEFI 4 system. In it, it states that when the key is first turned on you should have fuel pump run 2 seconds. The ECM sends a signal directly to the fuel pump relay and then after 2 seconds it does not receive an ignition signal it shuts power to the fuel pump relay. I wouldn’t think that coolant temp sensor or oil pressure sensor would be in that initial 2 second circuit.
    I would recheck the fuel pump relay fuse and the relay.
    fuel pump circuit photo.jpg
    Here is a copy of the circuit diagram. It should be the same as your boat. There is a procedure for diagnosing, but it requires a scan tool. Maybe the schematic can help you at least trace down the circuit. Hopefully there's nothing wrong with your ECM. Thats where the initial signal to the fuel pump relay originates.

  5. #15
    Join Date
    Jan 2021
    Location
    Columbus, Ohio
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    185

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    Quote Originally Posted by secondsupra2004 View Post
    fuel pump circuit photo.jpg
    Here is a copy of the circuit diagram. It should be the same as your boat. There is a procedure for diagnosing, but it requires a scan tool. Maybe the schematic can help you at least trace down the circuit. Hopefully there's nothing wrong with your ECM. Thats where the initial signal to the fuel pump relay originates.
    Huge help.

    What I see here is the ECM is the ground for the fuel pump relay (Dark Green/White) - Check continuity to ground while turning key to "RUN" position. This would assure that ECM is triggering.

    Check Pink wire from fuel pump relay fuse with ignition in "RUN" - should have +12V - if not check fuse or connection at fuse block
    If the relay is clicking - should be able to feel this also - when switched to "RUN" then control circuit is good.

    Another way to check is to test 87A (unused) on the fuel pump relay - it should have +12V at all times unless the ECM is telling the fuel pump to run. After 2sec, this should go back to having power, if the circuit is working correctly.

    Not sure where "FROM SYSTEM RELAY" is providing power, but this could be the problem if no power anywhere in this circuit, and fuses are all good.

    I know for certain, that the ECM will be in lockout mode and not start the engine for the other sensors I mentioned earlier, but the initial 2 sec run should function every time the key is switched and the gauges go through the reset process.
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  6. #16

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    Quote Originally Posted by Holdmybeer View Post
    Huge help.

    What I see here is the ECM is the ground for the fuel pump relay (Dark Green/White) - Check continuity to ground while turning key to "RUN" position. This would assure that ECM is triggering.

    Check Pink wire from fuel pump relay fuse with ignition in "RUN" - should have +12V - if not check fuse or connection at fuse block
    If the relay is clicking - should be able to feel this also - when switched to "RUN" then control circuit is good.

    Another way to check is to test 87A (unused) on the fuel pump relay - it should have +12V at all times unless the ECM is telling the fuel pump to run. After 2sec, this should go back to having power, if the circuit is working correctly.

    Not sure where "FROM SYSTEM RELAY" is providing power, but this could be the problem if no power anywhere in this circuit, and fuses are all good.

    I know for certain, that the ECM will be in lockout mode and not start the engine for the other sensors I mentioned earlier, but the initial 2 sec run should function every time the key is switched and the gauges go through the reset process.
    Check out this schematic- MEFI relay circuit. I beleive this is the "FROM SYSTEM RELAY" you mentioned.MEFI relay circuit.jpg

  7. #17
    Join Date
    Jun 2021
    Location
    Buffalo, NY
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    Thank you for the wire schematics- huge help! Unfortunately I did not see these until just now (been down at the boat all day).

    I have some developments- not sure exactly what they mean though. Let me know if this makes any sense to you guys:

    I removed the fuel pump relay. When I jump the wire from pin 30 to 87 the pump kicks on- so I have good power and ground for the pump itself.

    Now this is where things start to get interesting- The multimeter reads 12v on the control side of the circuit (female connectors for pins 85 + 86) when the key is in "run". I removed the two control wires form the connection housing and plugged them directly into the relay, no click and the meter reads 0v.

    Can anybody think of a reason why a circuit would drop to 0 volts when connected to a relay (again, the relay itself is fine)? Maybe a bad ground for the ECM? I'm looking for the ECM ground on these diagrams but I'm no electrical engineer. Does anybody know where it is in the physical world?

  8. #18

    Default No fuel pump power

    Check out a video on YouTube called
    GM FUEL PUMP RELAY TESTING . It about. 30 minute video and describes in detail the biased voltage produced by the ECM. 12 volts with a test light plugged in to the socket without the relay and 0 volts with the relay plugged in. Check it out.
    Last edited by secondsupra2004; Yesterday at 08:15 PM.

  9. #19
    Join Date
    Jan 2021
    Location
    Columbus, Ohio
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    185

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    Quote Originally Posted by Probably the Killswitch View Post
    Thank you for the wire schematics- huge help! Unfortunately I did not see these until just now (been down at the boat all day).

    I have some developments- not sure exactly what they mean though. Let me know if this makes any sense to you guys:

    I removed the fuel pump relay. When I jump the wire from pin 30 to 87 the pump kicks on- so I have good power and ground for the pump itself.

    Now this is where things start to get interesting- The multimeter reads 12v on the control side of the circuit (female connectors for pins 85 + 86) when the key is in "run". I removed the two control wires form the connection housing and plugged them directly into the relay, no click and the meter reads 0v.



    Can anybody think of a reason why a circuit would drop to 0 volts when connected to a relay (again, the relay itself is fine)? Maybe a bad ground for the ECM? I'm looking for the ECM ground on these diagrams but I'm no electrical engineer. Does anybody know where it is in the physical world?
    Pin 85 & 86 - are these wires Pink and Dark Green/White?

    The Dk Grn/WHT wire is ground. The ECM completes the ground for the circuit. A meter measures voltage differences between the wires. It looks like the relay is shorted and the wires have 12V on both, which is why you are measuring 0v potential difference.

    A new ice cube 30A 12V relay is $10. I would try it out and see what happens. You have one in your truck fuse box you could try out and see if it works.
    Last edited by Holdmybeer; Yesterday at 09:17 PM.
    2015 Moomba Mojo Surf Edition

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    1000lb lead (500lb under each rear seat)
    Manual wake tabs
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