Cummins Marine Diesel Repower Specialists › Forums › Cummins Marine Engines › 370 6BTA won’t rev beyond 2450 RPM

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  • July 5, 2022 at 10:33 am #133853

    J Grady
    Participant
    Vessel Name: Uncork & Unwind
    Engines: 370 Cummins
    Location: Olympia, WA
    Country: USA

    I have a 2003 Meridian 411 with 370 Cummins engines. I normally run at about 2300 rpms which puts the boat just up on plane. I was checking out a leak in my dripless and tried to run up to WOT a couple of weeks ago and found that my port engine would not rev past 2450. This engine is a Cummins factory rebuild that I suspect has about 1000 hours on it. The previous owner did not log the hours when changed. 

    The fuel filters are new. I took the air cleaner off, and inspected the inside for the turbo. It looked like the “good” turbo in Tony’s pictures. I also manually, moved the turbo blade and it rotated smoothly. I have also had the throttle linkage inspected and it is tight all the way from the station to the engine and it does go through the full range of travel. There is no black, white, or any kind of smoke coming out of the engine. Not even if I accelerate quickly. It runs absolutely fine. No missing, coughing, or sputtering. It just runs out of revs. It is almost like there is a governor preventing it from spinning up. I have also had the props and bottom cleaned with no change. Since the governor spring is in the fuel injector pump, is it possible that that pump is the issue? 

    Any ideas? I am lost.

     

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Viewing 11 replies - 1 through 11 (of 11 total)
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  • July 28, 2022 at 6:34 am #134766

    Francis Valerio
    Participant
    Vessel Name: overslept
    Engines: Twin 4BT CPL741
    Location: Massapequa Park, New York Long Island
    Country: USA

    Excellent….you DID have a lack of fuel BECAUSE the Injection Pump was UNABLE to deliver it due to the linkage.

    Glad you got it sorted out

    July 27, 2022 at 10:47 am #134735

    J Grady
    Participant
    Vessel Name: Uncork & Unwind
    Engines: 370 Cummins
    Location: Olympia, WA
    Country: USA

    It’s fixed!

    Now reving to 3200 in neutral.

     

    I had a retired mechanic check out the throttle response and he noticed that there was a dead area were the throttle would move, but there was no change in RPMs. He checked the linkage from the throttle cable to the engine and found that it was loose and slipping. Once tightened, the correct response returned. A simple, but hard to find fix. 

    July 11, 2022 at 3:47 pm #134097

    J Grady
    Participant
    Vessel Name: Uncork & Unwind
    Engines: 370 Cummins
    Location: Olympia, WA
    Country: USA

    Another neutral test

    I ran the port engine today with the fuel fill cap removed with the hopes that the issue was just the vent. Unfortunately, the symptoms did not change. I will need a mechanic’s help to blow out the lines, so I will be back to you all in a week or two.

    July 9, 2022 at 6:22 am #134022

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    If test was in “neutral, then you have something else going on besides just  “classic” fuel starvation..   Maybe “MAJOR” fuel restriction

    Next: Remove both return fuel lines from the engines– remove the fuel fill caps and use something to blow thru the return lines  to be sure they are both 100% clear and freely flow to the tanks–Listen for air or bubbles in the tanks. Be thoughtful doing this

     

     

    July 8, 2022 at 5:42 am #133984

    Francis Valerio
    Participant
    Vessel Name: overslept
    Engines: Twin 4BT CPL741
    Location: Massapequa Park, New York Long Island
    Country: USA

    The more fuel that you attempt by increasing RPMs will cause more vacuum in the fuel system and starve the engine.

     

    Like Tony said, you “may” have a restriction at the “pickup” tube that goes into the fuel tank….maybe clogged strainer (if there is a strainer, and if there is I would remove it)

    There is an “aneroid” page on this site, you just have to look for it.  The forum does not like to post links so just search it.  (You can actually google search it and it will link right to the sbmar website aneroid page)

     

    This is happening on ONLY one engine correct???

    Can you rig up some temporary fuel line to swap them from one engine to the other???

    July 7, 2022 at 4:06 pm #133974

    J Grady
    Participant
    Vessel Name: Uncork & Unwind
    Engines: 370 Cummins
    Location: Olympia, WA
    Country: USA

    Test was in Neutral

    Both fuel filters were new in November and only one tank of fuel has been used thus far. I did change the Racor again a week ago and no change in symptoms. 

     

    The test that I describe above the boat was in neutral sitting at the dock. And I don’t understand why the RPMs dropped part way through the throttle travel. If it was fuel starvation, would the response be the same through the entire range?

    July 7, 2022 at 3:35 pm #133972

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    Based of what you have posted, your symptom is classic fuel  “starvation”.  Could be fuel filters, ( you have at least 2)  the fuel pickup at the tank,  or anything in-between the engine fuel inlet and the bottom of the fuel tank… Properly installed vacuum or pressure gauges could tell the story

    I am making the assumption, your test was in gear under load?

    July 7, 2022 at 2:14 pm #133966

    J Grady
    Participant
    Vessel Name: Uncork & Unwind
    Engines: 370 Cummins
    Location: Olympia, WA
    Country: USA

    Throttle response

    I ran the engine at moorage today and got some totally unexpected results. I let the engine run at 600 RPMs for 15-20 minutes to get it fully warm. Then I tried running the throttle smoothly to WOT. What I found that it would rev to about 1800 RPMs, but as the opened the throttle more, the revs would drop by 200-300 RPMs for about a couple of inches of throttle travel! Then the revs would build again to about 2700 RPMs. I repeated this several times with the same result. I have never seen this or heard of these symptoms before. I have a video, but it is too large to post.

    I don’t know how to check the aneroid. Is there documentation on this?

     

     

     

     

    July 7, 2022 at 1:59 pm #133965

    J Grady
    Participant
    Vessel Name: Uncork & Unwind
    Engines: 370 Cummins
    Location: Olympia, WA
    Country: USA

    3050 RPM

    I got over 3050 RPM. The boat would go to 25 knots.

    July 5, 2022 at 6:01 pm #133878

    Francis Valerio
    Participant
    Vessel Name: overslept
    Engines: Twin 4BT CPL741
    Location: Massapequa Park, New York Long Island
    Country: USA

    also

    What was the maximum RPM you attained previously with this boat?

    you say you have no smoke or sputtering etc… Seems like you have a lack of fuel

    Did you check the aneroid???

    July 5, 2022 at 1:28 pm #133863

    Francis Valerio
    Participant
    Vessel Name: overslept
    Engines: Twin 4BT CPL741
    Location: Massapequa Park, New York Long Island
    Country: USA

    Will it hit WOT in NEUTRAL?  What are you getting in Neutral???  You should be like 3k or so …

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