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Mercury 150 won't start

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  • Mercury 150 won't start

    I have been posting in different areas with this problem but I need to start a new thread.... I have been having intermittent problems this summer with my Mercury 150 V6 EFI 97 model. It would die at times and wouldnt run at full throttle (idle only) then finally just died once and I never could get it started back at the lake. I take it home and it ran in the garage. I read on forums where bad fuel/lines or junk in VST could cause this so heres what I did... I replaced all the fuel and lines, I cleaned the VST tank and screen, It started for a second in the garage the first time after I got it all together then wouldn't start again......I verified spark in all 6 cylinders...I put a test light on the elec fuel pump while cranking and nothing.....the fuel pump has ran in the past few days but now it doesn't seem to have power going into the pump.....any ideas? could a faulty key switch cause this or is that just for cranking....I have had issues with it but not sure....also if it is the fuel pump why no power going to the pump during cranking?


  • #2
    Re: Mercury 150 won't start

    Ok I go out there and move the wires that lead to the fuel pump and it started working ...Now it starts great. I moved the wires around a lot and can't re-create the problem... I have to be able to trust it and as of now I don't. I have had this working before and then it wouldn't start again...I may have it pinpointed to the wiring that goes to the fuel pump but not sure....Does anyone know where these wires go? They are 1 red and 1 black from the fuel pump then down under the motor into a large wiring harness.....anyone know where they connect and maybe I can just put in all new wires to the fuel pump and see if that helps......

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    • #3
      Re: Mercury 150 won't start

      Manual shows a red and a red/purple going from the pump to the ECU.
      "A manual is a cheap investment"
      Fair Winds and Following Seas
      Bill
      PTC USN ret

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      • #4
        Re: Mercury 150 won't start

        If the ECU is going bad that is over a thousand dollars....Does anyone know if the fuel pump runs the entire time the engine runs? Could I just bypass the ECU and power the fuel pump from the switch or install a relay to power the fuel pump everytime the switch is on....or does the ECU run the fuel pump as needed?

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        • #5
          Re: Mercury 150 won't start

          [QUOTE][Does anyone know if the fuel pump runs the entire time the engine runs?/QUOTE]
          Yes it does....
          Could I just bypass the ECU and power the fuel pump from the switch or install a relay to power the fuel pump everytime the switch is on
          Yes....only problem is pump will put out full pressure all the time and is hard on regulator if you have long no wake zones to go thru..The ECU controls the ground to pump so pump speed varies.
          When in doubt,Trim it out!!!
          Business Owner & Certifed Technician
          Boats I own & use
          20ft Javlin w/250 Junkrude
          17ft Bullet w/200 Merc (SOLD!!)
          13ft Allison w/150 I-6
          17ft Hydra-Sport 175GT
          15ft Allison w/75 Stinger(project)
          14 x 48 Drifter with 1100SS Merc

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          • #6
            Re: Mercury 150 won't start

            Yesterday I checked the harness connector from the ECU to the wiring harness...There was very slight discoloration on the pin that went to the fuel pump and also it seemed like the female end of the plug on that same pin was widened. Is it possible that was my only problem? I put a small wire in there to make it tighter and cleaned it up. Going to the lake next week to test it...I hope thats all it was....I found out the ECU works the ground to the fuel pump and the power wire going to it was good......maybe this could help someone else.....Max

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            • #7
              Re: Mercury 150 won't start

              I took this boat out and it ran (so far so good) but there was one instance where when the boat was idling the speed kept going up and down... It wasn't subtle either it was actually climbing quite abit then dropping to normal idle speed. It was real windy and I didn't want to break down and fight the wind with the trolling motor so I wrapped it up and went home. Anyone know what could make the idle fluctuate like that? I have been having some trouble out of this engine all summer. I'm thinking about squeezing it and making a huge glass of lemonade......

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