Cummins 6BTA 5.9 330hp Ramdom Loss of RPM's comes and goes

[Rick Smith]

Good morning all. This issue has been coming and going for several months now. Sorry for the below detail but I think some background is needed, no help from 3 diesel tech’s thus far as they have/can not witnessed the problem when on board. In the starboard engine (545 hours) , all runs great, all gauges are normal no white smoke or black smoke. On the 4th we were our all day clocked about 60 miles engines ran great then approaching my marina after cruising at 2400 rpm for an hour, I once again ( 4th time in 3 months always at the end of day) started to lose RPM’s in the starboard engine. My RPM gauge slowly dropped from 2400 to 2200..2100..1900 could not bring it back up, the port engine was still at 2400 rpm’s. The next day took her back out to show a Tech could not get it to do the same all ran fine for the 30 min we were out max it out at 2900 rpm’s cruised at 2400 engine ran fine. This problem started about 4 month ago after losing a hose clamp on the Turbo hose. I have replaced that along with all other clamps and 2 hoses, double checked them, all is good with them. I have serviced the engine, new fuel filters etc. The after coolers were serviced in Feb 2018. This problem on the 4th was the first time in 3 weeks after about 25 hours, I thought it was resolved after replacing all fuel filters but here we go again?? Any input for troubleshooting would be great

Topic

[bradsykes27]

Hi Rick,

 

I know this is very old thread but just curios what you did to solve the problem? We are having the exact same issue now and our mechanic cannot seem to figure it out. We have had the fuel polished, changed all filters etc and still getting random losses of power later in the day. 

[Rick Smith]

A Good read

Wow the link you provided is a very good read! I thought I was up on diesel filtering systems this takes it to the next level. I have not tried troubleshooting tank venting, great suggestion and an easy tip when the problem is occurring. Thx for the input!!

[Rob Schepis]

It’s vacuum, not pressure.

Here’s how you handle crap in the tank — go boating and polish your fuel at sea as you pull 50+ gallons an hour from your tank, filter it, and send the majority back. BUT to do this you need proper diameter pickup tubes WITHOUT a screen at the bottom and you need a very capable primary filtration with a real mud filter, NOT a Racor that will be a service nightmare as it gets all full of crud.

Post some pics and specs on your current primary (off-engine) filtration.

Have you read this:

https://www.sbmar.com/articles/marine-fuel-filtration-the-seaboard-way/

How is tank access? Can you get the pickup out of the tank for inspection without too much boat surgery?

I removed my pickups on my current boat and made these new ones to get down closer to the bottom of the tank. 1/2″ dia copper pipe, no screens.

Just to cover another base — have you investigated that the starving of fuel could be related to tank venting? All that would take is to remove the fill cap once the engines starts to drop rpm’s and see if she recovers.

[Rick Smith]

Thx Rob!

I do not have a pressure gauge on the fuel filters, my last boat did and I am considering installing an upgraded fuel filtering system. I was pretty sure when I serviced them it solved the problem as the starboard filter was horrible but then it came back. I agree with your assessment due to the random nature of the problem. The supply hoses looked fine but that is not to say something in the tank. Just want to rule out any power issue, not sure what to do about allot of crap in a tank.

[Rob Schepis]

Do you have a vac gauge on your primary fuel filtration? Sounds like a fuel issue due to crap in the tank that starts to partially block off the pick up tube after you’ve been running awhile. Have you removed and inspected the pick up tube?

[Rick Smith]

Thus far that is correct, each time this has occurs it is always at the tail end of a pretty long day out. I have owned the boat for 6 months. The prior owner kept detailed notes about service, maintenance and problems, which were minimal. All service seemed to be meticulously done and at regular times. Of note last year he noted in the journal “Starboard Turbo not spooling up had it removed and bench tested all was well” no other comments about what caused the issue but it seems to me that that could be the same issue I am having? “no air = no rpm’s.”?

[Rob Schepis]

Sounds like this only occurs after long runs at full cruise. Is that correct?

[Author]

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