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  1. #1

    RPM Loss Update - Expurts needed!

    OK, DD gurus, here’s my latest. When we last saw our hero he was struggling to find his missing 200 rpm on the stbd engine.

    To recap, I had been running the boat for a 3 hour trip from New Haven Ct to Westerly RI at about 2150 rpm (DD 6v92 making 435 hp) when my stbd engine dropped to 1950 and would not come back up. After docking I changed out the filters again and that had no effect.

    I went thru the throttle linkage and the shutdown solenoid linkage and all were adjusted properly. I bypassed the floscan to eliminate that from the system. Suspecting the fuel pump, I read the manual and based on their recommendation, measured the return volume at 1200rpm for 1 minute. Flow was acceptable: recommended minimum is 0.8gpm at 1200; I was reading 1.1gpm.

    In doing so, however, I did note that there was a substantial amount of foam (air) in the returning fuel. Suspecting a leaking line upstream from the pump, I first tested the good engine and determined that there was no air in its return flow. I then replaced all the inlet lines to the offending engine and ran the good engine’s supply line directly to the fuel pump of the bad engine, but that had no effect on the foam in the return line. All fuel lines upstream of the fuel pump are now new and solid. I am definitely getting good clean fuel (no air leaking in) to the pump.

    Suspecting the fuel pump (cavitation?) I replaced it this morning, along with its fittings. I still have the same problem.

    One interesting hint is that when I cranked the engine to prime the new pump, with the output line disconnected from the secondary fuel filter that it feeds, fuel spurted up out of that filter (i.e. back out the inlet of the secondary filer). That suggests to me that the fuel already in the engine is somehow being pressurized back into the filter. I’m not sure what to look for from here. Suggestions would be appreciated. Thanks.
    Bob
    Everyone should believe in something - I believe I will go fishing - Henry David Thoreau

  2. #2

    Re: RPM Loss Update - Expurts needed!

    What a mess!! You are still sucking a little air from somewhere. Not enough to affect fuel supply, but still giving air to the injectors input.
    With the supply coming from the other engines line, That discounts the run to the tank, no? I personally think that you need to investigate further, ground thats already been covered. I would isolate given assemblies/sections of the run and cap them off and put a vacuum pump on it. They should hold absolute indefinitely. You may have a simple fitting with a hairline crack thats not visible to the naked eye. Even a crack in the Racor/threads.
    The next test would be to remove and plug the foamers supply and run a temp hose from the good ones filters to the bad one. Start the good one first, then fire up number 2 and check the return for foam. Just another way of isolating sections. If you can run a seatrial while hooked up like that, at least youll see if you can reach full load speed. The one pump at 1.8 should be able to supply both.
    The last test, altho tedious, would be to put a T and a valve in the secondary inlet. Run that one and crack the valve and check for air there. If that happens, then the leak is before the secondary. Actually, just after the pump is all pressure anyway. Just re-read the final line... Does the fuel return off the back of the heads have check valves ? That may explain the pressure but not the air. ws
    Last edited by yachtsmanbill; 06-03-2011 at 06:27 PM.
    yachtsmanWILLY

    I used to think I knew everything until I found the experts HERE; Now I know I dont know SQUAT



    www.flybridge.proboards.com
    Uncensored, no nonsense boating fun for adults

  3. #3

    Re: RPM Loss Update - Expurts needed!

    I'm fairly confident that I am not getting air in the line to the pump. The port (good) engine shows absolutely zero air in the retun. The stbd is loaded. I hooked up the port fuel line to the brand new stbd pump, with new fittings, and there is no change whatsoever - it is still loaded with foam.
    Everyone should believe in something - I believe I will go fishing - Henry David Thoreau

  4. Re: RPM Loss Update - Expurts needed!

    Bob, sounds like you know what you are doing, so this may be a waste:

    "I then replaced all the inlet lines to the offending engine and ran the good engine’s supply line directly to the fuel pump of the bad engine, but that had no effect on the foam in the return line.."

    So you extended the (non foaming) port engine fuel supply directly to the new stbd engine fuel pump.,.and still had foam in the stbd engine???? And also replaced all the stb engine fuel supply lines??

    If I got that right, I sure don't get it either..

    If not too much work, how about extending the stbd eng fuel supply (which may be suspect) line to the port engine fuel pump...if no foam in the port engine, then you KNOW the supply is good.....and the "leak" must be in the stbd fuel pump (even the input connection) or somehow after it.

    good luck...
    Last edited by REBrueckner; 06-04-2011 at 03:18 PM.
    Rob Brueckner
    former 1972 48ft YF, 'Lazy Days'
    Boating isn't a matter of life and death: it's more important than that.

  5. #5

    Re: RPM Loss Update - Expurts needed!

    If its not the pump could be a bad injector sucking air.
    "DON'T BELIEVE ANYTHING YOU READ OR HEAR AND ONLY HALF OF WHAT YOU SEE" - BEN FRANKLIN




    Endless Summer
    1967 50c 12/71n DDA 525hp
    ex Miss Betsy
    owners:
    Howard P. Miller 1967-1974
    Richard F Hull 1974-1976
    Robert J. & R.Scott Smith 1976-present

  6. #6

    Re: RPM Loss Update - Expurts needed!

    That was my next conclusion... Actually compression air pushing back through the inlector. Does the foam smell like burned fuel? ws
    yachtsmanWILLY

    I used to think I knew everything until I found the experts HERE; Now I know I dont know SQUAT



    www.flybridge.proboards.com
    Uncensored, no nonsense boating fun for adults

  7. Re: RPM Loss Update - Expurts needed!

    "If its not the pump could be a bad injector sucking air."
    "Does the foam smell like burned fuel?"

    Interesting ideas.... an injector can get stuck open??

    Would there be any accompanying tell tale signs...like smoke?? Would he lose only 200 RPM??
    Rob Brueckner
    former 1972 48ft YF, 'Lazy Days'
    Boating isn't a matter of life and death: it's more important than that.

  8. #8

    Re: RPM Loss Update - Expurts needed!

    Thanks for the replies. I spent most of yesterday working on it to no avail. I like the idea of extending the fuel supply from the foaming engine to the good one. That would absolutely eliminate the fuel lines as a problem if the foam does not travel to the good engine.

    I also suspect an injector problem. I discussed it with an Atlantic DD tech at some length on Friday and he told me that he has never heard of a 92 engine having an injector do that - 60 series do all the time, but not the 92. Still, something is causing it.

    And, I'm getting pressure where I should not. The right cylinder bank fuel supply line is getting back pressure. When I removed both fuel supply lines from the secondary filter, and cranked the engine, the right supply line spurted fuel back out in the direction of the filter. The good engine shows no such tendancy.

    I believe that the foam, loss of rpm, and back pressure are all related, and probably are the result of some sort of injector anomoly.

    Once I switch the offending engine's fuel line to the good engine and absolutely eliminate an air leak as the cause, other than starting to swap out injectors, I really don't know what else to do.
    Everyone should believe in something - I believe I will go fishing - Henry David Thoreau

  9. #9

    Re: RPM Loss Update - Expurts needed!

    One other thing - I did try to smell the foam, but the diesel smell is so strong I could not detect anything else.

    I also shot all 6 exhaust ports with an IR thermometer. The left bank was consistently 129 - 131 degrees and the right bank 133 - 134 consistently (after running 20 min or so).
    Everyone should believe in something - I believe I will go fishing - Henry David Thoreau

  10. Re: RPM Loss Update - Expurts needed!

    Maybe checking those exhaust port temps at low, neutral, RPM dockside (I'm guessing that's what you did judging from the low temps???) is not an adequate test to determine if one injector is faulty. I never checked any temps at idle, only at cruise RPM and found exhaust port temps within about 5 or 6 degrees via infrared thermometer.

    Perhaps a check of exhaust port temps at normal cruise, under load, would detect a cylinder with low temp (faulty injector) better??? ...and my own readings were sensitive to angle and distance from the exhaust port. If yours are painted, be sure to read consistently either on paint or on "rusty" spots....that affected my infrared temperature readings several degrees also.
    Last edited by REBrueckner; 06-06-2011 at 02:13 PM.
    Rob Brueckner
    former 1972 48ft YF, 'Lazy Days'
    Boating isn't a matter of life and death: it's more important than that.

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