Cummins Marine Diesel Repower Specialists › Forums › General Discussion › 480 ce hunting at low rpm

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  • March 1, 2022 at 6:34 am #127717

    sconrad208
    Participant

    I noticed my starboard engine began hunting at start up about 3 months ago.  i figured maybe it was related to the cold or maybe a dirty filter, but i’ve recently replaced the fuel filters and now the weather is warmer and it still “hunts” at start up.  here is what i’ve found so far: symptoms while sitting at slip

    • at cold start the rpms will fluctuate between 580 and 650
    • give her throttle about 900 rpms and she levels out….pull throttle back and she hunts again
    • pressed engine “sync” switch at low idle but no effect, engine still hunted
    • issue seems to go away after running engine for 30 min 
    • once she is warm there is not hunting at re-start

    symptoms while underway (within 10 minutes of cold start)

    • as soon as i put her in gear to leave the slip the rpm levels out….pull her out of gear she hunts again at low rpm…..go over 900 rpms and she doesn’t hunt.
    • after engine warms up the issue goes away

    this is only happening with the starboard engine…..where should i look first to correct this “hunting”. thank you sc         

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  • June 29, 2023 at 4:34 pm #150888

    sconrad208
    Participant

    Luistormenta…I am curious….did your mechanic swap pumps between engines?   Did it make any difference?  I’m curious.   Pretty much my only remaining step to determine if it’s the pump.   

     

    April 29, 2023 at 4:46 am #147388

    luistormenta59
    Participant

    I have the exact same issue with my  starboard 480 on my Tiara 38 2004 and my mechanic has tried “everything”and can’t correct the hunting 

    April 10, 2023 at 10:17 am #146247

    Jerry Palmer
    Participant
    Vessel Name: Tiara 3800
    Engines: QSC480
    Location: Channel Islands Harbor
    Country: United States

    Fuel Filters fixed mine….

    I know it sounds crazy and I have had a few people look at mine with no Solution. I had resigned to the fact I would just have to live with it, then I had my oil changed along with all of the oil and fuel filters and it stopped! 

    April 10, 2023 at 10:05 am #146246

    sconrad208
    Participant

    Update and Conundrum

    update and what i’ve done over this last year…..
    • tried the rack adjustment “thingy” but it didn’t change how the engine ran at idle
    • inspected the secondary throttle controls (located beside the helm) disconnected all the plugs, cleaned the pins, and reconnected……no change
    • performed valve adjustment.  some of the valve’s needed minor adjustments but none were out of the tolerances.  engine still hunted at idle
    • pulled injectors and had them tested.   3 of the 6 failed so i had them all rebuilt.  re-installed them but no change to idle hunting.
    • i swapped the plug wires behind the helm and used the good engines throttle pot (morse cable to electronic potentiometer)…no change
    • took the ECM’s to cummins and found they had the old software version.  had them load the latest version which is known to correct stumble stall issues Y90012.01.   I thought my problem would be solved but when i started the starboard engine it ran worse.  it basically hunted all the way through the movement of the throttle and bounced between 580 and 840 rpm’s now……which meant i couldn’t even shift into gear without “clunking” or damaging something.   my next step was bosch p7100 pump
    • looked at my p7100 pump and noticed it falls in the early pump category that had voltage issues at idle.  my pump number is 384 08 00034.  i took pump to get rebuilt at the certified bosch dealer and they recommended i replace the actuator which i did as part of the rebuild.  (it’s another known cause for the hunting at idle issue).  well, i just got my pump back and re-installed it knowing it would finally fix my problem…..it did not.   the engine continues to hunt at idle between 580 and 650 rpms.  it doesn’t bounce as high as it did after the ECM calibration, and i can put her in gear now, so i guess the re-build helped.  <br />
    • i pulled speed sensors from good engine and swapped with bad engine….no change
    • i pulled boost pressure sensor from good engine and swapped with bad engine….no change
    • finally called in the big boys, CUMMINs, and paid them to come to boat and figure it out.  Two Techs full day.
    • connected computer and no codes were present.
    • checked fuel system by running the engine on an isolated fuel tank….no change
    • checked voltage from alternator….no issue
    • pulled power wire off of engine heater…..no change
    • swapped ECM’s from good motor to bad motor…..no change
    • pulled wires off of speed sensors….no change

    what should i do next?   Could it still be the injection pump?  They provided a report showing they rebuilt it within Bosch’s specifications.

     
    The boat reaches full rpm on both motors, 2690 rpm….runs great!   Fuel burn is 13.6 at 2200 rpm.  no hiccups or sputters throughout the rpm range in gear.  no white smoke, black smoke, or blue smoke.  aftercoolers have been done in last year, including cleaned and pressure tested.  new fuel filters in the last month.   air filters cleaned in the last month.
     

    i am thinking it has to be a voltage issue because it goes away as soon as i put it in gear and only happens when in neutral at idle.   my concern is that it used to only happen when the engine was cold but now it happens all the time.  as soon as i pull her out of gear it hunts.

    March 27, 2022 at 6:45 pm #129473

    Jerry Palmer
    Participant
    Vessel Name: Tiara 3800
    Engines: QSC480
    Location: Channel Islands Harbor
    Country: United States

    Same exact problem 2005 Tiara 3800

    This problem existed before I bought the boat and now that I have finished addressing some more pressing problems I am back to this issue. Same engine, starboard side all of the exact same issues you mentioned including going away after warm up. Have you found a solution? My mechanic even swapped  the ECM from one engine to the other and still the same.

    wondering if this article has any thing to do with the issue  ?

     

    Cummins Marine 6CTA 8.3 M4 (480CE) Stall Stumble ECM Fix

    March 15, 2022 at 6:03 am #128717

    Steve Lewis
    Participant
    Vessel Name: Just Us
    Engines: Cummins 480CE
    Location: Marblehead, OH
    Country: USA

    Shots in the Dark………

    Fellow 480CE owner here………

    These are all just general ideas without any kind of certainty and in no particular order.   #1 You mentioned that once warmed up the hunting goes away.  So how about adding Wolverine oil pan heaters to warm the engines permanently?  Its a good practice to have them good and warm anyway so maybe this helps with the hunting as a side benefit.  #2 Have you removed the fuses that activate the intake air heater grids?  Maybe the current draw/voltage fluctuation of those is presenting in an interesting way? #3 have you read the “Stumble/Stall” article in Tonys’ Tips?  Maybe a firmware upgrade would help? #4 Maybe adjust the idle RPM up just a touch.  675rpm maybe?  Could be some weirdness there.

    I had our mechanic remove the fuses for the intake air heater grids while he was doing some other work.  I did not like the voltage fluctuation at idle that was evident until things warmed up.  I have Wolverines and installation is on the list of things to do in the next month and a half before spring launch.  We are up North in Ohio.

    I do not recall if I have the RPM fluctuation like you do but I will pay attention to it once we launch.  Not sure if any of this is helpful but it does not hurt to consider these.

    2 users thanked author for this post.
    sconrad208, Tony Athens
    March 15, 2022 at 5:00 am #128714

    sconrad208
    Participant

    Ok, i pulled the connectors apart at the electronic throttle control….checked for corrosion and/or loose wires but all looked good…i sprayed corrosion block into the connectors and re-connected….then i followed the harness back to the engine, separated each connector, checked for loose wires and corrosion, sprayed corrosion block into all the pin connectors and re-connected.  i also, dug the backup manual throttle controls out of the side of the helm and pulled the connectors along with the over-ride switch, checked them, and sprayed corrosion block into all the pin connectors and re-connected.   I didn’t see any evidence of corrosion or loose connections…..they all looked surprisingly clean and tight. i hoped that i had made a difference, but when i started the engine, the same thing occurred……the engine started hunting at idle……from 550 to 650…..steady back and forth…….give it a bit of throttle and it goes away. still curious what caused this engine to start hunting at idle and if i can fix it?

    March 1, 2022 at 11:59 am #127766

    Rob Schepis
    Forum Moderator
    Vessel Name: Tenacious
    Engines: 6BTA 5.9 330's - "Seaboard Style"
    Location: Long Island, NY
    Country: USA

    I’d start by going through all harnesses – unplug, clean, treat and reseat all connections.  All it takes is a little green in a connector on a voltage sensitive circuit and things can get erratic…  

    1 user thanked author for this post.
    Tony Athens
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