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Old 03-25-2018, 08:55 PM   #41
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Good thought.

If an electric pump was used and not shut down it definitely could .

I just dug out my PT fuel system shop manual and looked in the complaints list.

According to the Cummins manual, it is for trucks, there are two ways of this happening and both require a fuel level to be above the injectors.

FLOODED CYLINDERS can be caused by fuel levels above the injectors.
In the case of trucks by parking so the tank outlet is above the engine or if the tank is mounted in a manner that puts it above the engine.

The book suggests one method that should work to prevent that and that is a float chamber so a rising level in the chamber would raise a needle valve to close the line much like a carburettor.

So for Capt. Sea Fever this could happen again. His boat must have something odd with the installation and maybe combined with some other quirk it could happen again.

Ensuring the tank outlets fuel supply valves are closed, ensuring the return line check valve is working properly, the float chamber or as suggested an electric shutoff valve between the tanks and the PT pump that is energized/de-energized with the PT shutdown valve so there is double protection.

I looked at my own boat and in my case the tank fuel level would never be above the PT pump/engine.

I suggest to Capt. Sea Fever that he examine his system carefully, ensure the shutdown valve has new seals, check the checkvalve and replace it, figure out a system of ensuring the tank outlet valves are closed with a sign put over the starting positions, ensure the tank[s] vent hoses are clear and not obstructed in any way. That includes any dips that can hold fuel. Dips can act like a P trap and cause trouble. Ideally the hose should be a constant rise from the tank to the hull fitting actually to a point somewhat above the hull fitting and then down to prevent seawater splashes entering the tank.

It also sounds like it cannot happen overnight but if there is a fault in the check and shutdown valves then who knows.
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Old 03-25-2018, 09:02 PM   #42
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Originally Posted by twistedtree View Post
This is my understanding too. But I've additionally always understood that as part of all these systems, the actual nozzle tip is essentially a pressure relief valve that only sprays when the fuel is under high pressure. One of the checks of an injector nozzle is the drip rate which is the leak-by rate.
I thought so too. Looks like not unknown in the truck world but I'd never heard of it in the marine world although not a mechanic.

Evidently there is a quirk that can allow flooding of cylinders under the right[wrong] circumstances. It may also need a worn shutdown valve or , I'm guessing here, a worn return line check valve.
Or/and a worn or sticky injector.
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Old 03-26-2018, 08:29 AM   #43
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tidbits from a marine engineer with personal experience on these engines....

"A couple of guys are getting it. The injectors on the PT system operate backwards from most styles in that the nozzle is always open to the cylinder. Most injectors close the nozzle with the plunger "needle" and the sac or space between the needle and the nozzle holes is as small as possible. Modern systems try to eliminate the possibility of fuel in the sac in order to reduce emissions and prevent nozzle clogging with carbon. The OP's Cummins fills the sac as a way to meter the amount of fuel injected and the cam pushes the needle down to pressurize the fuel for injection. It does not make for a clean crisp start of injection like a pressure lift style valve, fuel begins to flow as soon as sac pressure is greater than cylinder pressure. This means for the start of injection the fuel is more of a drip or stream than an atomize mist.
The open sac also means that a worn injector with the cam stopped in the "wrong" spot could allow fuel from the rail to drip into the cylinder. In order to hydrolock the engine though it would have to either go for a very long time or have multiple injectors and fuel pump parts worn out way past replacement time. The oil level would have been extremely high ... the OP said that there was plenty of oil, it sounds like he didn't know what the level should have been. The dipstick on the VT555M is high above sump so unlike other engines it would not overflow but it would certainly be at cylinder level on the stick and obvious to anyone who looked at it. The only way a cylinder would hydrolock is after the oil level was at the top of the cylinders so that there was no way for the dripping fuel to drain to the sump.

We had those engines on our boat in Oxford so know them fairly well."
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Old 03-26-2018, 09:03 AM   #44
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Quote:
Originally Posted by psneeld View Post
tidbits from a marine engineer with personal experience on these engines....



"A couple of guys are getting it. The injectors on the PT system operate backwards from most styles in that the nozzle is always open to the cylinder. Most injectors close the nozzle with the plunger "needle" and the sac or space between the needle and the nozzle holes is as small as possible. Modern systems try to eliminate the possibility of fuel in the sac in order to reduce emissions and prevent nozzle clogging with carbon. The OP's Cummins fills the sac as a way to meter the amount of fuel injected and the cam pushes the needle down to pressurize the fuel for injection. It does not make for a clean crisp start of injection like a pressure lift style valve, fuel begins to flow as soon as sac pressure is greater than cylinder pressure. This means for the start of injection the fuel is more of a drip or stream than an atomize mist.

The open sac also means that a worn injector with the cam stopped in the "wrong" spot could allow fuel from the rail to drip into the cylinder. In order to hydrolock the engine though it would have to either go for a very long time or have multiple injectors and fuel pump parts worn out way past replacement time. The oil level would have been extremely high ... the OP said that there was plenty of oil, it sounds like he didn't know what the level should have been. The dipstick on the VT555M is high above sump so unlike other engines it would not overflow but it would certainly be at cylinder level on the stick and obvious to anyone who looked at it. The only way a cylinder would hydrolock is after the oil level was at the top of the cylinders so that there was no way for the dripping fuel to drain to the sump.



We had those engines on our boat in Oxford so know them fairly well."

Very informative, and good clarification of my previous understanding. But it sure would be nice if people could post directly rather than through surrogates.
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Old 03-26-2018, 10:11 AM   #45
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Technically, the position of the "rack" (attached to the power lever) determines how far the cam lobe can/will push the injector...which establishes the amount of fuel injected. Simple and effective designs, especially for a boat where the injector rack sees very little movement (wear), as opposed to a truck application where the rack is constantly moving with the accelerator pedal.
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Old 03-26-2018, 10:47 AM   #46
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Very informative, and good clarification of my previous understanding. But it sure would be nice if people could post directly rather than through surrogates.
Sometimes surrogates are required for those who aren't in favor with TF mods.
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Old 03-26-2018, 10:52 AM   #47
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Sea Fever
Are your tanks higher than the PT system? If no, this thread will require a turn to port.
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Old 03-26-2018, 02:12 PM   #48
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A little more info....

"Here's another correction.

The 555 does not have a "rack." The amount of fuel injected is determined by fuel pressure and the time available to fill the "cup" or injector sac. The distance "pushed" or stroke of the injector is the same at idle as it is a full power. The comment quoted is totally false and only confuses the issue further."
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Old 03-26-2018, 02:23 PM   #49
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A little more info....

"Here's another correction.

The 555 does not have a "rack." The amount of fuel injected is determined by fuel pressure and the time available to fill the "cup" or injector sac. The distance "pushed" or stroke of the injector is the same at idle as it is a full power. The comment quoted is totally false and only confuses the issue further."
I stand corrected. Was thinking Detroit. This link provides a decent description of the Cummins PT fuel system/design: http://www.liberatedmanuals.com/TM-55-4018-1.pdf
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Old 03-26-2018, 05:02 PM   #50
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and more from a marine engine expert....

" Fuel delivery quantity on a DD injector is determined by the closing point of the spill port which is determined by the rack position. The length of a plunger stroke is constant regardless of load and is determined by the cam profile. "
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Old 03-26-2018, 06:11 PM   #51
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and more from a marine engine expert....

" Fuel delivery quantity on a DD injector is determined by the closing point of the spill port which is determined by the rack position. The length of a plunger stroke is constant regardless of load and is determined by the cam profile. "
That is correct. By the way, the marine engine expert confuses the issue in the earlier descriptive post by characterizing the plunger in the Cummins injector as the needle. The pumping operation of this type of injector requires correct terminology for clarity. See the description of the injector design and operation in reference document I posted earlier.
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Old 06-12-2018, 03:14 PM   #52
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An UPDATE...
All of the injectors were cleaned and the injector pump rebuilt. Much water was found in the pump.
I installed new glasses in my Racors.
The engines are working fine.
Every half hour though I have to empty approximately a cup of water from the SB Racor...not the P Racor.
Since the SB engine repair last week I have discovered that the SB fuel tank hasn’t budged. All of the fuel for the SB engine is coming from the P tank despite the fact that the fuel tank valve on the SB side is opened during use.
My question....why is all the water accumulating in the SB Racor and none in the P Racor?
Also, I suspect that the SB fuel line is plugged.
Thoughts please?
Thanks
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Old 06-12-2018, 05:31 PM   #53
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Yes, check your fuel lines. Maybe you can blow them out? Do you have a sump/drain on your tanks? Could your tank vent be taking on seawater - perhaps the opening is angled forward? I would drain the stbd tank completely also, to be certain you have all the water out of it. If you have inspection ports, then clean any gunk from the bottom of the tank as well.

Maybe your fuel returns are unbalanced? The 555's do have a high return fuel flow, but it would be quite a coincidence that the return to Stbd would balance the draw, so a pinched or blocked line is more likely.
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