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2001 50 with 3406E RPM & GPH

Discussion in 'Post Yacht' started by B Dickinson, Jul 17, 2019.

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  1. B Dickinson

    B Dickinson New Member

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    Thanks for all the responses Gents. On the fuel burn from Capt. J - does the calculation take fuel returned to the tanks into consideration? When I refuel and do the math it does not seem that I am burning as much fuel as the displays show. Also, Capt. Ralph - all the work that was done by the yard was top notch, BUT, have not ruled out a dropped prop on reinstall. The tachs are fairly frustrating to interpret - CAT LCD displays and the readings are constantly jumping all over the place, sometimes as much as 20 RPM or more. Only had the boat since May and am working through all this "stuff" to be sure the engines are performing as they should and not in an overload situation. To that end, I have scheduled the CAT boys (guys here on the Chesapeake who I trust) to get on the boat with computer hooked up, sea trial and analyze exactly what is going on. This soiree will include replacement of the old "beer can" style TPSs with 21st century units. This not to occur until next month. Will report back findings/solution. Thanks again for all of your responses!
  2. Pascal

    Pascal Senior Member

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    Fuel flow on Cat display shows actual burn taking into account what is returned

    You can use the fuel burn totalizer to keep a fuel log. It is very precise. On 2000 gallon tank I m usually within 30 to 50 gallons when I refuel

    Tachs are very accurate, maybe too accurate and will indeed vary by 20 or 30 rpm depending on turn, list or waves.
  3. rtrafford

    rtrafford Senior Member

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    Had these engines. Know them well. Your WOT load throttle target is 2325.

    Interesting that the WOT no load shows a variance between the engines as well as throwing a code. There may be an issue here with a sensor that has the engine showing an RPM while running at another. These engines have about 50 sensors on each of them. Locate the throttle sensors and swap them between engines, rerun the test.
  4. rtrafford

    rtrafford Senior Member

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    The tachs on these engines are Cat displays, and they read what the ECM sends to them. Gotta start with settling the basis data by eliminating known errors. See both engines act the same under no load, then work from there. This could turn out to be a series of issues, even beyond a throttle sensor. For the moment I'd trust the props more than the data.
  5. Capt J

    Capt J Senior Member

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    I'm pretty sure on Pre - C series Cats that the fuel burn is calculated off of a base fuel map, that takes into account injector pulse, load, and rpm. I don't think it's as accurate as the C series fuel burn calculations. Don't get me wrong it's close, maybe 95% accurate or better......but not 99% + accurate that the newer C series computer does. Rpms can jump around 20 rpms at cruise with a little wave action as the boat is going up and down and over waves. I see as much as a 60 RPM swing with some engines and boats. A seatrial is a good idea. Also changing the aftercoolers if they haven't been done in 6 years is another good idea.
  6. B Dickinson

    B Dickinson New Member

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    Boost 23-24 @ 1850RPM
  7. Capt Ralph

    Capt Ralph Senior Member

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    Let me more correctly ask my question; are the boost numbers exactly the same between engines?
    My thought behind this is the fuel consumption will differ if there is not the same turbo boost pressure in air box.
  8. B Dickinson

    B Dickinson New Member

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    Boost on one is 23 and 24 on the other @1850.
  9. Capt Ralph

    Capt Ralph Senior Member

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    Well that's close. Should not make a difference in RPM or power.
  10. Capt J

    Capt J Senior Member

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    What's fuel pressure at cruise on each motor?
  11. PtJudeRI

    PtJudeRI Senior Member

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    I have the same setup as well. Generally, at 1850-1900 I see 23 boost, Fuel Press Should be between 65-80 psi for optimal running, and a fuel burn rate of 24-26 gal/hr. per side.

    If your fuel press. gets below 50, I would be changing racors, maybe on engines as well. I generally do my racors 3-4x per season, but I do a few hundred hrs. a year of running too.
  12. B Dickinson

    B Dickinson New Member

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    Something is up with my rig. At 1850 I am always at 30-31 gph. CAT guys on boat now and sea trailed to gather all data yesterday. Installing present day throttle position sensors for starters.
    Will report back any significant findings.
  13. Capt J

    Capt J Senior Member

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    Sounds like you're running a lot of load at 1850. Is the bottom and props clean? Do the engines hit 2300 WOT?
  14. B Dickinson

    B Dickinson New Member

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    Bottom and props clean and wheels just redone in order to hit 2300 WOT full load which they are not. CAT boys analysing data now.
  15. B Dickinson

    B Dickinson New Member

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    OK, final analysis after Cat guys on the boat. Two sea trials with computer hooked up and TPS units replaced. Now have full throttle response range from 0 thru 100%. Starboard engine fine, reached WOT and all data just fine. Port engine slightly overloaded to be corrected with another prop tune on that side as all data is also fine, aside from not reaching WOT. Don't know why my rig seems to burn more fuel than other identical boats aside from the fact that I always carry a lot of fuel - hold 870 and usually carry minimum of 1/2 to 3/4 load.
  16. rtrafford

    rtrafford Senior Member

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    To be clear, you're running CAT 3406E-800? And if so, why is the discussion that WOT is 2300 when it should be 2325? WOT under no load should be 2415. But certainly under full load the target is 2325.

    On these engines, fwiw, if you lose fuel pressure and performance, those manual fuel pumps are typically garbage. Use them once, and their seals are compromised, sucking air. In the final days I replaced the pumps, and vowed to never use them. I installed an electric system and plumbed the engine to allow me to use that pump to prime, etc.
  17. rtrafford

    rtrafford Senior Member

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    Also, the props should be tuned to provide 2325 WOT with full wet load. If you aren't achieving the RPM your engines are overloaded. Don't tune to a 50-75 percent load.