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Old 12-09-2019, 01:09 PM   #1
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Occasional power loss on one engine

We are heading south in a twin-screw heritage East trawler with Cummings 5.9 BTA engines. our fuel tanks have a crossover line that is open between the two of them to keep the tanks level. we stopped at top rack in Norfolk and put a hundred gallons in each tank which topped them off. My port engine every once in awhile will drop from 1800 RPMs down to a thousand, with a noticeable power loss, and then shoot right back up to where it was. there is no common factor sometimes it happens a half hour after the last little hiccup sometimes it's three hours after and the other day we went all day and it only did it once. we've changed filters I have inspected everything and cannot find any air leaks in or fuel leaks out. I realize it may be beyond my paygrade but I was wondering if anyone out there had any ideas of what I should look for.


John & Donna Bedell
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Old 12-09-2019, 03:23 PM   #2
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I would start with the basics, have you checked the fuel filters? Maybe some air getting into the fuel lines?
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Old 12-09-2019, 03:27 PM   #3
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If the engines are supplied by separate tanks it may be debris in the tank that momentarily blocks the pickup tube. I once found a flattened piece of bubble gum that floated around and occasionally blocked the pickup. Later when cleaning the tank, found about a dozen toy soldiers.
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Old 12-09-2019, 03:48 PM   #4
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You can also try to loosen the fuel fill cap (enough to let air in) on the bad side and see if that helps. That would eliminate or confirm a blocked vent.

You could also have a fuel line that is delaminating and closing partially.
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Old 12-09-2019, 06:45 PM   #5
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Is it a mechanical throttle control, or electronic?
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Old 12-09-2019, 07:16 PM   #6
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You have had some good suggestions from above.

The fuel shutdown solenoid which controls the valve on the injection pump for shutdown OR run has been known to cause difficulties. It is attached to the throttle linkage on the engine at the injection pump. If the linkage is maladjusted or loose it may allow the actual valve to partly close choking off fuel. Check that the solenoid itself is also secure.

Poor electrical connections could also cause the solenoid to lose some power again allowing the linkage and the valve to move from open position. The return to off spring is quite strong.

One good way to help narrow the source down is the use of a vacuum guage mounted just after the filter. Get one with the telltale needle so the highest vac. can be read afterwards. Designated Engineer is one source. Of course look immediately but that is not always possible so the telltale will stay untill reset. THis way you will know if the problem is supply before the filter or after.


And yes, T.T. has a good question, is the engine mechanical or electronic control.
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Old 12-09-2019, 07:46 PM   #7
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Quote:
Originally Posted by jtbedell View Post
We are heading south in a twin-screw heritage East trawler with Cummings 5.9 BTA engines. our fuel tanks have a crossover line that is open between the two of them to keep the tanks level. we stopped at top rack in Norfolk and put a hundred gallons in each tank which topped them off. My port engine every once in awhile will drop from 1800 RPMs down to a thousand, with a noticeable power loss, and then shoot right back up to where it was. there is no common factor sometimes it happens a half hour after the last little hiccup sometimes it's three hours after and the other day we went all day and it only did it once. we've changed filters I have inspected everything and cannot find any air leaks in or fuel leaks out. I realize it may be beyond my paygrade but I was wondering if anyone out there had any ideas of what I should look for.

John & Donna Bedell
Full Time Cruising
Heritage East 44
-I would close the crossover until you sort it out in case one tank is stirring debris. If as others have said debris blocks outlet the crossover then feeds both engines. Once closed port engine may stop completely if port tank outlet is blocked.
-which tank was filled first? May offer a clue. I gather this started after tank fill.
-drop from 1800-1000 sounds like momentary blockage or air, it may also be a failing fuel pump.
- "sometimes it happens a half hour after" after what? the RPM drops and then 1/2 hour later you lose power, or 1/2 hour before RPM comes up again?
-when did you change filters, before or after this started. As someone said there may be an air bubble left behind and not yet cleared.
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Old 12-09-2019, 08:02 PM   #8
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That’s what I was experiencing for a year or so before the engine finally quit.

Later I found that replacing the Racor 500 fuel filter cover eliminated the symptoms. The new cover is relying less on webbing and more on sheer metal mass. The engine hasn’t slowed down or quit since I installed the new heavier cover. I surmised that air was leaking into the top of the filter because of flexing in the cap that promoted warping of the gasket surface enough to admit air.

This should be a recall in my opinion.
And if I’m confronted w a new Racor product in the future I’ll remember this filter event.
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Old 12-09-2019, 08:43 PM   #9
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If you have screens on the bottom of either pick up tube in the tank. Pull the tubes and pull off the filter screens, don't replace them.

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Old 12-09-2019, 09:40 PM   #10
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If you have screens on the bottom of either pick up tube in the tank. Pull the tubes and pull off the filter screens, don't replace them.

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Yes, I agree no screens on the pickup tube. You want the debris to come out of the tank and go into the filters where you can remove it.
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Old 12-10-2019, 06:58 AM   #11
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"Yes, I agree no screens on the pickup tube. You want the debris to come out of the tank and go into the filters where you can remove it."

Except when the chunk of gunk is able to block or plug the pick up tube.

A rolled screen or bag screen fastened on the end of the pick up tube could be 6 inches long and would be hard for multiple chunks to block.
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Old 12-12-2019, 05:45 PM   #12
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I also believe your problem is NOT fuel filter related, because that would only get worse as time goes by. Its just a guess, but to me it seems more like air getting into the system. Engines are able to purge small amounts of air.

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