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  1. #1

    Default Engin limp mode and backfires

    Hi good day. I bought a boat with a 4.3 mpi mercruiser in it. It were running fine no problems . But now it goes into limp mode after about 10 or so minutes and in beginning it did not back fire now it does . Took it to a workshop and they tested it and it came up with no faults on scanner. So I went pick it up and went straight on water started up perfect running smooth and then after about 10 min starts backfiring and cuts out on limp mode only running on 3 cylinder not 6. Called work shop up and mechanic recons he can't see any thing on scanner. Things I did . Change feul filter, 6 new spargplugs, check roter and dizy cap all good . Check the shift interup switchall good. Any ideas what to check next please. Low idle it don't back fire only under load in water. Outside with earplugs on it only goes into limp mode no backfiring .
    Last edited by ATTIE; 12-20-2017 at 05:43 AM.

  2. #2
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    Default Re: Engin limp mode and backfires

    this seems to me like it is running out of fuel. Is it an older boat? Are you using fuel with ethanol in it? You may have some restriction in the fuel line somewhere. Do you have VST on it?
    Practicing the ancient art of ren-ching

  3. #3
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    Default Re: Engin limp mode and backfires

    Time for a fuel pressure gage at the injectors to see what's going on.

    Jeff

  4. #4
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    Default Re: Engin limp mode and backfires

    a good mechanic with the scanner should be able to identify the root cause soon after it happens....I'd suggest a thorough diagnosis without speculation if you want to find the issue in the least time. Not everything" is monitored by the computer......

  5. #5
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    Default Re: Engin limp mode and backfires

    Find a better shop.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  6. #6

    Default Re: Engin limp mode and backfires

    The mechanic did test the boat with scanner and it's not commig up with errors just the normal ones . My next thing is to find out what will cause the motor to go into guardian mode and start checking them . Did check 1-shift interup switch 2-iac valve 3-feul presure. What can the other be do you know will browse the Internet to see if I can find out more info. The boat is only 8 years old only 173 hrs on motor . Change out all spargplugs and feul filters . Feul filter clean no dirt or water in it . Thanks
    Last edited by ATTIE; 12-26-2017 at 04:20 PM.

  7. #7

    Default Re: Engin limp mode and backfires

    Ok scanner picked up low oil pressure so hopefully it's only a sensor that's faulty otherwise need to pull motor to change oil pump.

  8. #8
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    Default Re: Engin limp mode and backfires

    You can always hook up a mechanical oil pressure gauge to confirm oil pressure. If the new sender don’t do the trick.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  9. #9
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    Default Re: Engin limp mode and backfires

    Quote Originally Posted by ATTIE View Post
    Ok scanner picked up low oil pressure so hopefully it's only a sensor that's faulty otherwise need to pull motor to change oil pump.
    You do realize that Mercruisers low oil pressure threshold is around 7PSI (SEVEN) ? Highly unlikely that the oil pressure is your problem.

    All of this could just be RF From the ignition coil.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  10. #10
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    Default Re: Engin limp mode and backfires

    Check for true TDC with a piston stop tool and then check the base timing.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  11. #11

    Default Re: Engin limp mode and backfires

    Thanks for your guys help really appreciate it. Timing is good it missing because of the Guardian mode only 3 cylinder firings. The mech going to install a manual oil gauge to confirm oil pressure. I read that if boat stands to long the oil pump must be primme to avoid this from happening never done it before. It's not likely that the oil pump will fail but never know.

  12. #12
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    Default Re: Engin limp mode and backfires

    You do realize that Mercruisers low oil pressure threshold is around 7PSI (SEVEN) ? Highly unlikely that the oil pressure is your problem.

    All of this could just be RF From the ignition coil.

    As far as priming the oil pump........You were Definitely given the wrong information.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  13. #13
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    Default Re: Engin limp mode and backfires

    Quote Originally Posted by ATTIE View Post
    The mechanic did test the boat with scanner and it's not commig up with errors just the normal ones . My next thing is to find out what will cause the motor to go into guardian mode and start checking them . Did check 1-shift interup switch 2-iac valve 3-feul presure. What can the other be do you know will browse the Internet to see if I can find out more info. The boat is only 8 years old only 173 hrs on motor . Change out all spargplugs and feul filters . Feul filter clean no dirt or water in it . Thanks
    Translation: I don't know much about this boat. I'm too poor/cheap to pay for real service on it so I hope to troll the web for a free diagnosis that I can fix for cheap.
    I wish we had a free/cheap answer for you. You are not giving us enough information so we have nothing but wild guesses
    Practicing the ancient art of ren-ching

  14. #14
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    Default Re: Engin limp mode and backfires

    Quote Originally Posted by o2batsea View Post
    Translation: I don't know much about this boat. I'm too poor/cheap to pay for real service on it so I hope to troll the web for a free diagnosis that I can fix for cheap.
    I wish we had a free/cheap answer for you. You are not giving us enough information so we have nothing but wild guesses
    Most accurate this I have read on this forum.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  15. #15
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    Default Re: Engin limp mode and backfires

    Just by the symptoms it sounds heat related to me. A hot engine can make the oil pressure to drop also. Did they scan it when the problem was present? Did you clean all of the electrical connectors in the engine harness? Pull all connectors apart and clean with electrical cleaner and put back together with dielectric grease. Sand all ground as metal to metal. Watch the temp gauge close and see if the issue corresponds with engine temp? On a car the computer uses fixed values (open loop) until around 120 degrees and them uses the inputs or goes closed loop for efficiency. RF noise can also play a part keep all plug and coil wires away from the engine loop.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  16. #16
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    Default Re: Engin limp mode and backfires

    Quote Originally Posted by kimcrwbr1 View Post
    Just by the symptoms it sounds heat related to me. A hot engine can make the oil pressure to drop also. Did they scan it when the problem was present? Did you clean all of the electrical connectors in the engine harness? Pull all connectors apart and clean with electrical cleaner and put back together with dielectric grease. Sand all ground as metal to metal. Watch the temp gauge close and see if the issue corresponds with engine temp? On a car the computer uses fixed values (open loop) until around 120 degrees and them uses the inputs or goes closed loop for efficiency. RF noise can also play a part keep all plug and coil wires away from the engine loop.
    Ignition coil
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  17. #17
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    Default Re: Engin limp mode and backfires

    [QUOTE=Docksidemarineservices;595374]Ignition coil[/QUOTE
    thats another possibility if the ignition coil is getting hot install a ballast resistor to coil pos just make sure the ignition module is getting battery voltage.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  18. #18
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    Default Re: Engin limp mode and backfires

    [QUOTE=kimcrwbr1;595383]
    Quote Originally Posted by Docksidemarineservices View Post
    Ignition coil[/QUOTE
    thats another possibility if the ignition coil is getting hot install a ballast resistor to coil pos just make sure the ignition module is getting battery voltage.
    These coils are prone to failure and RF leaks that scramble the ecm , set off the alarm and shut the engine down. No codes.

    http://www.marineengine.com/newparts...m=MER8M0054588
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  19. #19

    Thumbs up Re: Engin limp mode and backfires

    Hi Thanks for your guys input. Just to defend myself here the boat is at a dealership and a qualified mechanic is looking at it so I'm not looking for a cheap answer. They did run it on lake and start of running well till it heats up and loosing oil pressure they did change oil sensor and the problem still there they going to drain oil and replace oil and filter they suspect wrong oil is been used they going to test it and install a manual guage to confim oil presure . That's the code what they get when they test it . I was just hoping to get some more info maybe somebody on here had the same problem. Thanks for all the advice much appreciated.

  20. #20

    Default Re: Engin limp mode and backfires

    Thanks guys problem fixed been oil presure only getting 5psi change oil and oil filter oil sensor all good now . Wrong oil been use by previous owner.

  21. #21
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    Default Re: Engin limp mode and backfires

    Jeez iss, if the oil was killing it, I wonder what the heck kind of oil was in it? In the future, you can be pretty safe using straight SAE 30. Wal mart has it in large jugs.
    Practicing the ancient art of ren-ching

  22. #22
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    Default Re: Engin limp mode and backfires

    Quote Originally Posted by o2batsea View Post
    Jeez iss, if the oil was killing it, I wonder what the heck kind of oil was in it? In the future, you can be pretty safe using straight SAE 30. Wal mart has it in large jugs.
    You cannot use straight weight oil in a roller engine.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  23. #23
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    Default Re: Engin limp mode and backfires

    OK, I'll back up 30 years and stop doing that!
    Practicing the ancient art of ren-ching

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