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Mercury 225 EFI 4 Stroke Fuel/Spark Problems

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  • #1

    Mercury 225 EFI 4 Stroke Fuel/Spark Problems

    A friend of mine offered to let me use his boat the last weekend of snapper season since we had already planned the trip and he couldn't go at the last minute. The boat performed and ran flawlessly. After a great trip with no problems we topped the boat back off with non-ethanol fuel (22 gals) and cleaned up the boat like it was ours.

    A few weeks later he went to use the boat and it wouldn’t start. He noticed the separator on the engine had water in it (indicated by the red ring) and the engine would not fire. He told me the water separator between the fuel tank and the engine had water as well but it had been a couple of years since he changed it. He drained the VST tank and installed a new separator filter but never got it cranked. He said it didn't appear that the VST even had any water in it but said it would not fire at the plugs.


    It's a mystery to me as to why it would not fire when it ran perfectly when I turned the key off the last time it was used. It seems highly unlikely that something would fail sitting on the trailer. But something definately has.

    After doing a little research and troubleshooting we know that the fuel pumps are not cycling with the key but will run if you jump them out. There is no power at the pumps at all. What would cause the engine to not fire and the fuel pumps to not work?

    I understand the the ECM grounds the pumps but does the ECM need too see fuel pressure before the engine fires?

    Can someone tell me what function the LP fuel driver serves and what powers up the driver?

    Fuses are good and even tried to crank the engine with a different wiring harness so no broken wire from the switch.

    Any ideas on trouble shooting this? This is also one of the 2002 Merc/Yam motors. Any help would be appreciated.
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  • #2
    even though this is a Yamaha forum i will say something to you as i have worked on nearly all the motors in my life time as you would know mercury used to be the best motor until Yamaha start building its owned but then mercury did come a long way and couldn't regain it market share due to its motor blowing up without any reason and they grabbed their reputation as a good anchor,to cut the story short i will be checking the fuse on the main engine as it seems like it has blown off ,this could have happened as your friend could have accidentally touched the wrong terminals with the battery wire
    when you say it works with jump lead its definitely the fuse

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    • #3
      Thanks for your reply. I should have stated Yamaha in the description. Althought it was sold by Mercury it was built by Yamaha that year. I wished it was a simple as a fuse but they all have been tested and replaced. If I knew how the driver and the relay worked I could possibly figure it out. The wiring diagram I have isn't much help, it's more of a block diagram and not a true schematic that shows how things actually work. I need to know what the driver does and what fires the relays.

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      • #4
        madchard

        you do not know sh-- about motors or boats!!

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        • #5
          you are correct on some of the F225 and F200 mercs were yamahas with a black dress.
          merc did make the engine hood.
          other than that for several years it was a Yamaha.

          the fuel pump should run for about 3 seconds at key on power.
          if it wont then you have an issue.
          fuel pressure is NOT monitored by anything.

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          • #6
            Sequence of events a secret?

            Originally posted by rodbolt17 View Post
            you are correct on some of the F225 and F200 mercs were yamahas with a black dress.
            merc did make the engine hood.
            other than that for several years it was a Yamaha.

            the fuel pump should run for about 3 seconds at key on power.
            if it wont then you have an issue.
            fuel pressure is NOT monitored by anything.
            Thanks rodbolt You seem to have a wealth of knowledge on these engines. Care to elaborate on the sequence of events? Key energizes ??? that then energizes ??? to energize fuel pumps. Is this commom to the plugs firing as well? This is starting to appear to be a big secret. Also will the YDS software perform a diagnostic test with the motor not running?

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            • #7
              no start

              I can not tell you how many times I'm working on a boat in a harbor and hear someone cranking a motor with a no start !! I'll go over to lend a hand and always ask if the lanyard kill switch is hooked up.........sheeplessly...I see the owner reach over and hook it up,,, and BINGO !!...**** ON !!

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              • #8
                quick lanyard elimination test.
                pull it and hit the key, if the alarm sounds the circuit AND the horn works.
                plug it back in and continue.

                at key on the yellow wire powers up the ECM.

                now the ECM is going to latch the ground for the IGN relay and toggle the HP pump relay ground for about 3 seconds.
                .
                its also going to supply the 5V sensor reference to the various sensors that require it.

                low pressure pump wont toggle until after the engine is running and then at engine speeds below 1200 RPM it runs 10 seconds on and 20 seconds off and is con*****ed by the ECU toggling the driver ground not the relay ground.

                ign system is a standard TCI(12V) waste spark ign that rarely gives a problem.

                only real "issue" I have ever seen with the F200/225 is the ISC mechanically sticking and overheating the ECU.
                this can cause ign coil meltdown and ECU meltdown.

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