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Old 12-02-2010, 01:31 PM   #41
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RE: Small Surges in RPM Every Few Minutes.

Quote:
GonzoF1 wrote:Would a leak there build up and then surge enough air into the pump to have it surge?
It's kind of hard to leak air into a higher pressure area.
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Old 12-02-2010, 01:46 PM   #42
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RE: Small Surges in RPM Every Few Minutes.

Good point.

Waiter? CHECK PLEASE!
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Old 12-02-2010, 03:08 PM   #43
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RE: Small Surges in RPM Every Few Minutes.

Tom Gonzo
Its pretty hard to have group therapy trouble shooting, which is going on here.

I was suggesting that you pull the filters now that have 70 hours on them in order to eliminate that as any possibility. Do one thing at a time and each time go try the boat afterwards to determine which action really was the solution.
If you replace those 2 micron filters and it still surges then move on to the next possible defect in the system. It doesnt matter if you use 2 micron or 10 at this point. You just need to get new and clean filters there to ensure that is not the source of your problem.
Your use of biocide could have killed the micro-kritters in the fuel and loosened them up, sending them to the filters.
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Old 12-02-2010, 03:20 PM   #44
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RE: Small Surges in RPM Every Few Minutes.

How does a clogged filter cause a speed increase?

A clogged filter restricts the passage of fuel, causing a decrease in speed. Unless of course it is a magic filter that unclogs suddenly every 7 or 8 minutes for a second or two.
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Old 12-02-2010, 04:34 PM   #45
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RE: Small Surges in RPM Every Few Minutes.

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RickB wrote:

How does a clogged filter cause a speed increase?

A clogged filter restricts the passage of fuel, causing a decrease in speed. Unless of course it is a magic filter that unclogs suddenly every 7 or 8 minutes for a second or two.
Trust me... I thought the same thing. I figured it was a diesel thing.
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Old 12-02-2010, 04:49 PM   #46
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Small Surges in RPM Every Few Minutes.

It's not a "diesel thing." Any decrease in fuel flow will result in less power and less power into a fixed pitch propeller means a decrease in rpm.

A gas engine can speed up momentarily because the mixture goes lean but a diesel will just sag if the fuel flow is restricted. A filter restriction reduces fuel pressure and the engine will slow down.

A very small air leak doesn't change the fuel pressure, it just displaces a tiny amount of fuel that the governor can easily compensate for. When the air suddenly goes away the pressure is the same but more fuel is available for the same delivery setting and the engine speeds up momentarily until the governor inertia is overcome.

Maybe you had an air leak and didn't know it but changing the filter cleared the leak?

-- Edited by RickB on Thursday 2nd of December 2010 05:50:59 PM
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Old 12-02-2010, 06:39 PM   #47
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RE: Small Surges in RPM Every Few Minutes.

*


****

RTF, what does my being bi/trans gender have to do with it?* They where questions that I have/had and still do.*

On the way to the boat, I call my diesel mechanic, stop by the Everett Marine store to pick up some things and ran into their head of maintenance, they both said if the leak was before the Rocor filter that the bubbles could/might be seen, but the air would be trapped in the top of the filter canister.* So if there was an air leak it*should be after the filters.

So if you dont agree then please explain why?

*
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Old 12-02-2010, 08:56 PM   #48
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RE: Small Surges in RPM Every Few Minutes.

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Phil Fill wrote:RTF, what does my being bi/trans gender have to do with it?* They where questions that I have/had and still do.
Finally "outing" yourself? I can't speak for RTF but since you have been alluding to your peculiar fascination with women's clothing and such for a few years now, it has become fair game if not tiresome. Get over it.

As far as bubbles in the Racors, most of the Racors fitted to small boats are so oversized as to not even work as designed with such low flows as they see. In that type of installation a near microscopic bubble would be all but invisible anyway and would be very unlikely to make it out the little "turbinator" thingy.
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Old 12-03-2010, 07:32 AM   #49
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RE: Small Surges in RPM Every Few Minutes.

Rick, Our diesel certainly will speed up when the filter becomes clogged. The injector pump will suddenly try to push more fuel through and then it will decrease as the vacuum builds and then increase until the engine finally shuts down. The engine will surge at least 100 RPMs or more than when it is running normally when this starts. We have run offshore for days with the engine running and then get a clogged filter and the engine begins to hunt. This has happened to us more than a few times unfortunately. A quick shut down before the engines dies and a filter change fixes the problem without having to bleed the system to get it started. We have had this happen with our original Perkins and then with our new Yanmar after a re-power. Chuck
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Old 12-03-2010, 07:56 AM   #50
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RE: Small Surges in RPM Every Few Minutes.

I really don't want to get into one of those endless internet pissing matches about this thing but an engine surging or hunting because it is running out of fuel is not an engine that runs along producing normal power then momentarily increases power by a couple hundred rpm for a second.

If your engine speeds up it does so because it is getting more fuel, not less. If it hunts or surges it is moving both sides of the governor setpoint and that is the way that mechanical or hydraulic governors work, they repsond to inertia. If the fuel supply is constant the hunting is damped very quickly. If the fuel supply is varying it can exacerbate the hunting problem.

If the OP wants to change every filter on the boat that is fine with me, they are not my filters or my expense.*I just believe the problem is an air leak and not a fuel starvation issue and provided the reasons I think that way and a method to troubleshoot the issue. Take it or leave it.
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Old 12-03-2010, 10:34 AM   #51
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RE: Small Surges in RPM Every Few Minutes.

"If your engine speeds up it does so because it is getting more fuel, not less"

Sorry to disagree but that is simply not true to my experience. I had a Perkins and when I had fuel clogs it sped up..increased RPM momentarily. This happened 2 or 3 times to me just before it shut down due to lack of fuel.
This also happened once on my Cummins 6BTA when the filter was just starting to clog up. I was able to reduce rpm and limp into an anchorage and change the element.
And now that I am writing this is also*how it happened on*my Lehman 120 before she shut down due to filter clogs.
*
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Old 12-03-2010, 10:52 AM   #52
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RE: Small Surges in RPM Every Few Minutes.

Regardless of theory Rick, I have to agree with these other posters. Every time I have had a diesel engine shut down due to fuel starvation, it surged before it died...much like a gasoline engine going lean. You can talk diesel engine theory all you want but this is real life fact. SO dig into the recesses of your brain and knowledge and tell us why...but please don't tell us we are imagining things. There is obviously a reason for this. If you can't explain it...fine. If not, then...................
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Old 12-03-2010, 11:50 AM   #53
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RE: Small Surges in RPM Every Few Minutes.

What would cause it to do it fairly regularly? Does the filter suddenly release pressure after several minutes of being clogged? Like a s;low build-up? Then, does the extra rpm surge kind of reset the filter and repeat the cycle?

On the other side... How would a tiny air bubble cause a surge?

Just trying to learn here folks... let's not make a big contest out of this!
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Old 12-03-2010, 12:59 PM   #54
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Small Surges in RPM Every Few Minutes.

When a diesel is starved for fuel by a clogged filter*and cannot maintain the setpoint of the governor, the governor increases the delivery stroke, it tries to add enough fuel to maintain speed. Your throttle does not set the amount of fuel delivered, only the speed you want the engine to operate.

As the engine slows, the amount of fuel*throught the lift*pump also*decreases but*some fuel continues to*move through the filter until there is enough to fill the injector pump bores again and the governor, now at full delivery, surges above the set point for a moment until the governor responds by reducing delivery and/or the fuel pressure again drops below a sustainable level. That creates a momentar and very observable surge.

In this case, just like I said, the engine surges or hunts on both sides of the setpoint before it quits or settles at a much reduced output.*It*can not run continuously above the set point because if it doesn't have enought to run at say, 1500 rpm, it surely doesn't have enough to run at 1600.

Tachometers have inertia as well, a tach needle will rise and fall well above and below the actual reading. When an*engine surges due to fuel starvation it slows down audibly then if or when*it picks up again it sounds like it is going faster.

I stand by my statement that an engine running at a constant speed that shows small speed increases, not proceeded by a speed decrease, has a small air leak, not a clogged filter.

You hear what you hear, the engine hunts due to governor inertia and the tach needle swings wildly due to mechanical inertia. What you see and hear is not always what is going on.

Gonzo, the governor will supply the volume of fuel*the engine*needs to produce the speed (power output) you have set. If there is a small air leak that aerates the fuel, the governor will deliver a slightly higher volume to make up for the air content. The engine only responds to the weight (available energy)*of fuel that is injected and aerated fuel contains less energy for the same volume*than "solid" fuel. If the air leak is stopped, as vibration and boat movement can cause, the sudden delivery of "solid" fuel will allow the engine to speed up.*Always keep in mind that the*governor responds to speed changes, it doesn't anticipate them so*it so it takes a moment to dampen any change. Since you don't report seeing or hearing*a speed reduction, only a very momentary speed increase, the symptoms point to an air leak, not a fuel starvation issue.

Practice follows theory very closely in marine diesel engine operations. Many commercial marine diesel installations are instrumented well enough and often trend monitored to the level where all the events I described can be very clearly observed in real time*or after an engine failure due to fuel starvation caused by any number of reasons. I can honestly tell you that what you think you see and hear is not always what is going on.

-- Edited by RickB on Friday 3rd of December 2010 02:00:25 PM

-- Edited by RickB on Friday 3rd of December 2010 02:07:21 PM

-- Edited by RickB on Friday 3rd of December 2010 02:35:18 PM
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Old 12-03-2010, 01:41 PM   #55
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RE: Small Surges in RPM Every Few Minutes.

Check your vent for the fuel tanks. If it or they are clogged, it can cause the engine to surge. Mud wasps have been known to take residence in vents.

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Old 12-03-2010, 02:17 PM   #56
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RE: Small Surges in RPM Every Few Minutes.

Okay Rick.....now I am seeing signs of lawyer/politician here!!!!...."....I know that what you see and hear you think is real....but don't worry, I am here to tell you that it is not real".....hahaha!!!


Just jackin' with you amigo!!! *In your defense, if could be a lag in RPM followed by a "surge" to the original set point making it seem like a surge.....but I don't think so. *Luckily I have only witnessed this phenomenon twice and once was on a friend's boat.
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Old 12-03-2010, 02:48 PM   #57
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RE: Small Surges in RPM Every Few Minutes.

Quote:
Baker wrote:Okay Rick.....now I am seeing signs of lawyer/politician here!!!!...."....I know that what you see and hear you think is real....but don't worry, I am here to tell you that it is not real".....hahaha!!!


Just jackin' with you amigo!!! *In your defense, if could be a lag in RPM followed by a "surge" to the original set point making it seem like a surge.....but I don't think so.**
No problem, it's difficult to put this stuff into less than a thousand words sometimes. And I learned a long time ago to avoid making statements online that don't allow for every known exception or statistical outlyer.

Sag, surge, lag, even the description is subjective and when the ear is involved and an analog tach display with a needle that can swing a few hundred rpm either side of the actual rpm with a minor change in signal level, what we see and think is often very much at odds with what is happening.

That is why we installed data loggers on big ship powerplants, most of the time you were covered in s****t before you even knew it was near the fan and had to read the logs to figure out what really happened when and why.



*
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Old 12-03-2010, 03:35 PM   #58
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RE: Small Surges in RPM Every Few Minutes.

Surges do not necessarily mean RPM going above "set point." Surges I have experienced are due to RPM dropping as fuel starvation occurs, hihger vacuum frees up gunk and then engine speeds up back to original set point.

This same exact thing occurs when I shut of the fuel supply to the filters to see if the racor vacuum gauge is working properly.
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Old 12-03-2010, 05:28 PM   #59
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Small Surges in RPM Every Few Minutes.

I don't know if it drops slightly and slowly before the surge (I haven't known to look, but will next time)... BUT... it DOES go above the set point and back down to it less than two seconds. THAT I am sure of.

*EDIT* BTW... I am going to change the filter FIRST (and check the vent ). It's the easiest and cheapest option. Then I'll run it and try something else (look for air leak probably) if it's still there.

-- Edited by GonzoF1 on Friday 3rd of December 2010 06:32:43 PM
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Old 12-03-2010, 09:40 PM   #60
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RE: Small Surges in RPM Every Few Minutes.

Quote:
GonzoF1 wrote:... I am going to change the filter FIRST
I'm betting that the filter is the culprit.

*
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