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Old 12-24-2011, 07:18 AM   #1
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Cummins 6BT Loses it's prime

My port Cummins 6BT loses it's prime....any suggestions...thanks
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Old 12-24-2011, 07:45 AM   #2
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RE: Cummins 6BT Loses it's prime

Find and fix the air leak.
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Old 12-24-2011, 07:52 AM   #3
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RE: Cummins 6BT Loses it's prime

RickB gave the short answer. Now the question becomes where is the most likely place for the leak to be. I think I'd start with the fuel filter. It's got gaskets and o-rings that can leak and it's often opened to change the filter. The rest of the fuel system rarely gets messed with.
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Old 12-24-2011, 08:00 AM   #4
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Cummins 6BT Loses it's prime

Yes you have an air leak. I would start with the Racor style filters as already suggested. If that doesn't solve the problem then you need to touch every connection you can find with a wrench to make sure it is tight. Make sure any clamps are tight.

No sense in talking steps after that until you do the above.

*

*


-- Edited by jleonard on Saturday 24th of December 2011 10:00:48 AM
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Old 12-24-2011, 08:25 AM   #5
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RE: Cummins 6BT Loses it's prime

What fuel system maintenance was performed in the days or weeks prior to the engine losing prime?
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Old 12-24-2011, 09:44 AM   #6
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RE: Cummins 6BT Loses it's prime

I thought it was the fuel pump, so I installed a new one and it wotked well for about 30 hrs, now the same problem.
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Old 12-24-2011, 10:23 AM   #7
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RE: Cummins 6BT Loses it's prime

Quote:
candyannwilliams wrote:
I thought it was the fuel pump, so I installed a new one ...
*

Boat maintenance advice:

Don't throw parts at a problem. That requires trips to the parts store and getting dirty changing them. It is easier to just throw the money over the side.

Test the parts you suspect before buying new ones. Unless you need a spare, your time and money is probably better utilized elsewhere.

Before you pick up a tool, pick up a pencil and paper. Write down the symptoms of the problem. Write down recent repairs or incidents even though you think they may not be related.

Read what you wrote.

Read the manufacturer's operator's or maintenance manual with particular attention to the troubleshooting section.

Approach the problem from one direction and stick to it until you have excluded the usual suspects.

Now, with that in mind, you say the engine is "losing its prime" does that mean it starts for a moment then stops because there is no fuel in the filters?

What kind of engine is it? Gas? Diesel?

How old is the engine? How many hours?

Is this a recent problem?

Did this suddenly happen or were there isolated occurrences over some period before it became a problem?

Does it just not start at all?

Do you have to bleed the injectors to start the engine after it has sat unused for some length of time?

How long does the engine have to sit before this problem shows up?

How do you restore the "prime?"

Are there any fuel weeps showing anywhere on the engine or fuel lines?

Does this happen if you shut off the tank valves after use?*
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Old 12-24-2011, 10:43 AM   #8
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RE: Cummins 6BT Loses it's prime

Rick, thanks for your quick response and help....here are the answers to your above questions:
The engine is a Cummins 6BT5.9 Diesel-1988 model
It only has 700(give or take) hours
It is a recent problem and there haven't been isolated occastions of it happening before
It doesn't start at all.
The enjectors or bled to start if unused for a time
20-30 minutes
The prime is restored by bleeding the injectors.
The fuel lines have been gone over and there isn't any sign of weeping
The fuel tanks are below the engines.

Again Rick Thanks for your help.
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Old 12-24-2011, 01:02 PM   #9
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RE: Cummins 6BT Loses it's prime

H'mmm

There is a little "bleed screw" on the center of the banjo fitting that comes out of the fuel filter. If you open that and crank does fuel immediately squirt out or does it take a while?

If you had that banjo fitting off, did you replace the copper crush washers with new or anneal them?

Are you absolutely positive that there is no weeping of fuel on any of the lines or connections when the engine is running?
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Old 12-24-2011, 01:29 PM   #10
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RE: Cummins 6BT Loses it's prime

also make sure that the return line is not loose,or letting air in it has been said that it will* drain the fuel from the engine inj.* it happened to me once
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Old 12-24-2011, 01:52 PM   #11
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RE: Cummins 6BT Loses it's prime

Thanks so much for the information-I'll check the banjo fittings in the morning and look back at the fuel lines (when I get her running again) Again I really do appreciate your help. Have a merry Christmas.
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Old 12-24-2011, 01:55 PM   #12
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RE: Cummins 6BT Loses it's prime

Thanks Jerry...I will also make sure that the return line is not loose,or letting any air in. Have a good one
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Old 12-24-2011, 01:56 PM   #13
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RE: Cummins 6BT Loses it's prime

Thanks Jerry...I will also make sure that the return line is not loose,or letting any air in. Have a good one
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Old 12-26-2011, 04:33 AM   #14
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RE: Cummins 6BT Loses it's prime

Most fuel systems have a check valve somewhere in the system.

Sounds like yours is leaking.

IF you install a fuel cut off at the tank, as the USCG required on 7pax and up boats ,

you might solve the problem , and gain a safety feature as well.
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Old 12-26-2011, 05:30 AM   #15
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RE: Cummins 6BT Loses it's prime

Thanks....we appreciate the tip.
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Old 12-31-2011, 06:04 AM   #16
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RE: Cummins 6BT Loses it's prime

Please let us know the ultimate solution.
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Old 12-31-2011, 11:41 AM   #17
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Cummins 6BT Loses it's prime

If I understand correctly, your engine "loses prime" while standing for a short period of a few weeks (or less?) while not running.
We have a similar 6BTA5-9 (1999) with 2,500 hrs. and have never had any need to re-prime the fuel line even after 7 months of winter storage.
I would have to concur with others that there must be an air leak somewhere on the delivery side. The only other question I would ask (and am unable to answer)
is whether there could be some pressure in the return fuel line (closed/clogged valve, kinked line etc) that might somehow present as a similar problem.
As with Doc, would sure like to know the answer--- it could be my problem next!!

Chris


-- Edited by Chrisjs on Saturday 31st of December 2011 01:43:01 PM
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Old 01-01-2012, 07:24 AM   #18
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Cummins 6BT Loses it's prime

Quote:
Chrisjs wrote:
If I understand correctly, your engine "loses prime" while standing for a short period of a few weeks (or less?) while not running.
We have a similar 6BTA5-9 (1999) with 2,500 hrs. and have never had any need to re-prime the fuel line even after 7 months of winter storage.
I would have to concur with others that there must be an air leak somewhere on the delivery side. The only other question I would ask (and am unable to answer)
is whether there could be some pressure in the return fuel line (closed/clogged valve, kinked line etc) that might somehow present as a similar problem.
As with Doc, would sure like to know the answer--- it could be my problem next!!

Chris



-- Edited by Chrisjs on Saturday 31st of December 2011 01:43:01 PM
*I would tend to agree with Chris on this one. The issue pretty much has to be in the delivery side, as the return side is open to atmosphere already.

You should see fuel somewhere.

Check for**fuel while the engine is running (anywhere after the lift pump), or fuel while the engine is sitting (anywhere prior to the lift pump).

The fuel has to leave the injection pump in order for the engine to loose its prime. It has to go somewhere. If there's no fuel then the problem is logically in a area that has no pressure or a vaccume*while the engine is running and no or little standing fuel (creating pressure) while the engine is at rest.

*


-- Edited by ksanders on Sunday 1st of January 2012 09:40:18 AM
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Old 01-01-2012, 08:48 AM   #19
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RE: Cummins 6BT Loses it's prime

Thanks for your suggestions....we are still trying to track the problem down...as soon as we get it figured out-we will let you know.** (we are taking the dayt off-LOL) Have a happy new year!
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Old 01-04-2012, 09:09 AM   #20
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Cummins 6BT Loses it's prime

I had a leak issue that I turned over to a mechanic(I would recommend you might do the same). It drove him crazy trying to find it. It turned out to be the remote Racor vacuum gauge that was nowhere near any other fuel system part. It was a strandard clear flexible tube that ran from the fuel "manifold" to the remote location(Main elec panel). He would not accept a penny of payment because he was so irritated with himself for not finding it sooner.


-- Edited by Baker on Wednesday 4th of January 2012 11:10:01 AM
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