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Old 09-28-2015, 10:03 AM   #1
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Cummins 6BTA drop in RPM

I was out yesterday in VERY rough weather. The girlfriend was on board and I told her my main concern was the plugging of the fuel filters in this kind of weather. What concerned me more was I was feeding both engines out of the same tank. In any event, we turned around. The weather was pretty hairy and there was no good reason to continue. When we turned away from the weather to run downwind, I noticed the right engine would ocassionally lose 200 RPMs. It very well could have been doing that up to this point but I would not have noticed due to the mayhem that was going on. Anyway, the weather was too rough for me to go look at the vacuum gauges and leave lil mama at the helm. SO I went with it and made it back to our (new) destination. I had already called ahead of a landside pick up so by the time I had the boat squared away, we left.

So....obviously...the first culprit would be the fuel filters. Would you just immediately go down and slap new filters on or would you go out and test them to confirm on the suction gauge before replacing?

And also, if that is not the case, what else could it be?

PS...there is probably about 75 hours on the filters. They have been running out of their respective tanks. All I am trying to say is that while both engines were feeding out of the same tank at the time, the filters have had different lives and have been exposed to different tanks over their lifetime.

PSS....I am not terribly worried as I think there is a very good chance it is the filters. But just asking to arm myself with more info when I get back down to the boat.
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Old 09-28-2015, 10:45 AM   #2
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I agree, filters. Classic case of rough weather "cleaning" tanks. Cant you look in the bowl at fuel condition?

If you have recording gauges then they might tell the story.

If you have those dumb closed spin on filters without the clear bowl the only way to tell is to cut them open.
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Old 09-28-2015, 11:14 AM   #3
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I agree, filters. Classic case of rough weather "cleaning" tanks. Cant you look in the bowl at fuel condition?

If you have recording gauges then they might tell the story.

If you have those dumb closed spin on filters without the clear bowl the only way to tell is to cut them open.
Bowls are clean. I would think the main reason for clear bowl is to see water. And I have been meaning to get the recording gauges...but I have not yet. I will after this event.
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Old 09-28-2015, 11:52 AM   #4
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Almost certainly fuel related. Intermittent blockage may be the pick up tube in the tank. Something big floating around in there that blocks the pick up once in a while? Maybe not, that would shut the engine down.
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Old 09-28-2015, 12:08 PM   #5
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Could a fuel hose be collapsing on the inside ?
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Old 09-28-2015, 01:22 PM   #6
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Was it bad enough that water was being forced up one of your exhausts, are they under the waterline?
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Old 09-28-2015, 01:37 PM   #7
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Was it bad enough that water was being forced up one of your exhausts, are they under the waterline?
Yeah it was bad enough(with the engines off and the boat rocking). But I was running the engines pretty hard. I don't think it could have fought upstream like that.
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Old 09-28-2015, 10:28 PM   #8
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Sounds exactly like a filter plugging to me. I had exactly the same thing happen in July under similar conditions. Changed the filter and immediately cleared the problem.

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Old 09-28-2015, 10:35 PM   #9
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Sounds exactly like a filter plugging to me. I had exactly the same thing happen in July under similar conditions. Changed the filter and immediately cleared the problem.

Ken
Yeah, pretty much what I am expecting....
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Old 09-29-2015, 06:24 AM   #10
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I have had two cases of fuel filter/pickup tube plugging and both acted like what you describe. The pickup tube plugging was a check valve at the top of the fuel tank that plugged with snot. Unscrewed it and blew it out and all was fine.

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Old 09-29-2015, 07:02 AM   #11
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No big deal to install the vac gauge AT the console.

If you purchase one get the differential pressure style , you can tell if its the tank suction line or the filter it self.

You should be able to switch to the second filter set for each engine with out entering the engine space.
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Old 09-29-2015, 09:45 AM   #12
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what my fuel got stirred up under similar conditions the fuel in the bowl was cloudy.
You don't have a prefilter in front of the racors do you?
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Old 09-29-2015, 11:51 AM   #13
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Originally Posted by bayview View Post
what my fuel got stirred up under similar conditions the fuel in the bowl was cloudy.
You don't have a prefilter in front of the racors do you?
Nope. Would the filters catch the crap before it got to the bowl??...other than water....which could make things cloudy?
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Old 09-29-2015, 11:51 AM   #14
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Quote:
Originally Posted by djmarchand View Post
I have had two cases of fuel filter/pickup tube plugging and both acted like what you describe. The pickup tube plugging was a check valve at the top of the fuel tank that plugged with snot. Unscrewed it and blew it out and all was fine.

David
Thanks David!! That is the kind of info I am looking for in case the simple filter swap does not solve the issue.
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Old 10-08-2015, 11:02 AM   #15
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I just wanted to say thanks for all of the input. It was definitely the filters as we had expected. I was going to change them anyway since I had an upcoming long trip. Anyway, I did change them and test drove them for about an hour and all was fine. ANd then headed out on my long trip and everything worked perfectly(aside from the milk crate debacle). I put about 400 gallons thru the engines in the last week and suction levels were fine and the engines ran perfectly. Thanks again!
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Old 10-08-2015, 11:05 AM   #16
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No big deal to install the vac gauge AT the console.
While not a big deal, it does introduce a significant risk for air leaks. On a previous boat, I had a remote gauge and it was a source of air into the engine. Perkins do NOT like air. I went through everything on the engine and then finally called in for help. How he found that leak, I never would have thought to look there. But that is exactly where it was. So just know that you are adding a source for air to leak into the system if you add a remote guage with a long tube run.
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