Small Surges in RPM Every Few Minutes.

Hiya,
** Edited my post (changed VC to VP) so it should make more sense-hopefully.* Mr. ralphost, I fully agree the filter SHOULD be the first suspect when experiencing fuel problems but simply changing from a 10 to a 2 micron filter should NOT cause problems on the OP's motor.* I interpreted his post being that as soon as he changed from a 10 to a 2, he started experiencing problems but after 70 hours it could quite possibly be a clogged 2 micron filter.* That being said, how many hours on the SECONDARY* filters and what size are THEY?

FF, now c'mon - who replaces their brake fluid every 2 or 3 years?

RT, you are assuming Gonzo used theright racor filters. The**500s are not always a good fit for the*someolder racor filters - so says racor. And Gonzo's problem started soon/immediately after his latest primary filter change using 2u primaries*---------- and could he*have*overloaded the on engine filter with crud from the primary during the change ------*he did not have the 10u filters he had used in the past ------------ and he possibly did not changeout the racor*O ring or added a second one -------- and a 2u primary is putting a lot of faith in diesel fuel which most suppliers only filter to 30u, if that.

But, if I were a dirty shirt boat mechanic for hire, I would not suspect the filters since the owner says they are fine. I would instead look over and check the rest of the system first and turn in a big trouble shooting bill.

-- Edited by sunchaser on Thursday 2nd of December 2010 07:46:53 AM

Hiya,
** Mr. sunchaser.* As you noted (and rightly so) there are a LOT of "ifs" and I don't know the circumstances of Mr. Gonzo's situation other than the surging which suggests some sort of fuel system problem.* I stand by my earlier statement that a clean 2 micron primary filter, properly installed, alone, SHOULD not cause Mr. Gonzo's symptoms and that a thorough going over of the COMPLETE fuel system is in order, starting with the simplest things first.
** I don't think this "problem" necessitates the hiring of a mechanic as a fuel system compared to an electrical system is pretty simple and Mr. Gonzo can only benifit by increasing his knowledge of HIS boat by doing it himself.
** There have been a lot of very good suggestions thus far and I anxiosly await to hear what the cure will be.

"And Gonzo's problem started soon/immediately after his latest primary filter change ..."

I think Mr. Gonzo should weigh in on that. I can't find any such statement anywhere under his name.

Gonzo wrote:

"...the current 2mic filter only has MAYBE 50-70 hours on it."
***************************************************************

My trusty mechanic tells me that I should change my Racors even if they have low hours if they have been in the boat for several months. He says that they can deteriorate over time plus get dirty with use. I once had a Racor 1000 go bad with only 20 hours but it had been in the boat for 6 months.

My 2 cents again.

RickB wrote:

"And Gonzo's problem started soon/immediately after his latest primary filter change ..."

I think Mr. Gonzo should weigh in on that. I can't find any such statement anywhere under his name.

Click to expand...

Then weigh-in, I shall... Oh, and please y'all... Call me Tom Gonzo is an old nickname from my audio engineering days.

*

Ok... So... Where was I... Oh yea - There are a lot of unknowns on my part. I can't assume, confirm, or verify the specific time these little surges began. TBH, I just didn't make a mental note of it the first time it happened. I have been feeling them for a while, but as I am still sorta new to all of this and am still becoming "in tune" with the zen-like awareness of boating. Especially with diesel technology and what to look for, feel for, and listen for.

I know it's been going on for a while, but whether it has been 6 months, 8 months, or a year... I would be lying to you if I said I knew for sure. That was the purpose of this thread. It was to sniff around your brain stems to learn what I could about a problem that has finally made it to the top of my "ask-the-smart-guys-at-the-trawler-forums-list-about"

I can say that it DOES appear to be increasing in frequency. I think I was timing it last week at about seven minutes between surges. I can say that I use Bio-Side last year...* it was too long ago (August) that I topped off the tanks for the first time. Not too long after that, I replace the filter a couple of times and I had the injector pump cleaned and checked while chasing another unrelated problem that ended up being the starter. The most recent "change" was the unintentional move to the 2mic filter.

What does all this mean? Well, to me, nothing. It's just a pile of note-worthy things I have worked on in the past year. Do any of them REALLY point to the problem I am feeling? Perhaps none of them, or a combination of a few, or ALL do, but like I said, I can't point at a moment in time when it started happening for sure. Thus, it's time to ask my team for possible solutions and tests to try and find out where to start looking.

I certainly hope it's just a filter,* but with history as a barometer, I ain't holding my breath. I'll start looking... break something major in the process... figure out a way to throw hundreds of dollars at the problem... only to find out there was a kink in some line that I didn't see the first 25 times I looked. Still, I hope that the real fix will require a a big bottle of wine, a few strippers, some baby oil, silk sheets, and a trapeze.

Anyway, this is quickly turning into a Marin-length post, so I'll wrap it up.

I now have a good list to start on to try and work this problem out. My sincere thanks for that. Please keep the thread going if there is more to add. I am try to absorb information about marine diesels when I can. There ae so many systems I still need to learn about (san the waste tank and I loathe the day I have to go down THAT road). I really have to learn them AS they become problems because I would quickly get swamped if I tried to learn it all right now. So I live-and-learn. I still have the genset, reverse-cycle A/C, and like I said... the waste system to get on the radar. All part of the excitement of boating, it seems.

I know this was a lot of BS that didn't help any, but it was fun to write.

Well, fwiw Tom, I am an alumni of the same mechanics school as you. Take it apart, break the part or something nearby, cut your hand in the process, throw money and time at it, realize there was an easier way to do the job, put things back together and finish the job. Get a drink and pat yourself on the back. Then, come Monday morning, wonder why all of your muscles are rather stiff and sore. The strippers etc. sounds like a good ending.
Mike
Baton Rouge

I change the primary Rocor filter and the engine filter every year. However, when we first got the boat ever 100 hours which took several years and they where still good.* So how long can filters last sitting in diesel?**The rule of thumb is*one year or 100 hours which ever comes first.


*
One of the first thing I had done was added an electric fuel pump help bleeding the engine and to transfer fuel from one tank to another as the Webasto draws from the port tank,* the 671 draws from the starboard and the gen set from the middle.* I try to keep each separate and filtered/polished.* The reason is if there is a fuel problem I can keep it in one tank, change to another tank, and polish/clean the one tank.*
*
It would seem you if the leak is before the Racor filter you should be able to see the bubbles in the bowl.* I look at a diagram on a Racor filter, the fuel first goes into the sediment bowel then up into the canister/filter.* So it would also seem like air would be trapped at the top as the in and out connection is in the middle of the filter?* So if you can not see bubble and/or no air is trapped in the top, then it*should be*after the Racor filter? The reason I bought two 180 gph filters is to filter the water/sediment and trap the air?* At least that is what I was told when I bought them?
*
Anyway, I would check and do the simplest before taking the fuel lines apart. If it persists I would call a diesel mechanic.* The more you change things the hard it will be for a mechanic it figure out, and while he is there ask him to give the engine a general check over as you can learn a lot by asking questions and watching. **I have my diesel mechanic double check and do things so if I really need him at least he knows who I am and familiar with the Eagle maintenance.****
*

Hiya,
** No Phil/Fill you won't be able to see bubbles in the Racor bowl.* Stick to what you KNOW-manicures and dresses!
** Mr. Gonzo take note of the question marks Phil/Fill puts after his statements-as USUAL, he hasn't got a clue.* Ignore his advice.
** The suggestions made by the other listees are all valid and again, fuel systems are pretty simple so the solution should be simple as well.* No need to call in a mechanic just be systematic in your approach.**Do/change ONE thing at a time.* If you do/change multiple things and effect a succesful repair, you won't know what the "fix" was.
** I would suggest you purchase a cheap set of flare nut wrenches...
http://www.harborfreight.com/catalogsearch/result?category=&q=flare+nut+wrenches
* They're far superior to regular wrenches when working on fuel fittings as they less likely to round off*a fitting.* Better still, for $10 buy 2 sets.* Remember: Righty tighty, lefty loosey.
** Start at one end of the system and work your way to the other, again doing ONE thing at a time.
** Mr. Gulf Comanche.* Mr. Gonzo NEVER suggested the trapeze etc. was the ending!

I already have "brake line" wrenches

One thing I mentioned earlier, but forgot to re-mention is the small leak at the top of secondary filter. Hard-line banjo bolt AFTER the lift pump... I wonder if that might be the source of the air leak. IIRC, I didn't have the right size o-ring in the secondary filter kit when I changed it in the spring. However, I still have a small leak that requires me to put a small piece of absorbing mat there every couple of week.

Would a leak there build up and then surge enough air into the pump to have it surge?

It all seems to be coming back to me know. I wonder if I recall the surges beginning then? I'll ask The Carbon First Mate Unit. She might know when it started.

GonzoF1 wrote:Would a leak there build up and then surge enough air into the pump to have it surge?

Click to expand...

It's kind of hard to leak air into a higher pressure area.

Good point.

Waiter? CHECK PLEASE!

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.
R.

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.

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.

Click to expand...

Trust me... I thought the same thing. I figured it was a diesel thing.

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

*


****

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?

*

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.

Click to expand...

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.

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

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.

"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.
*

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...................

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!

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

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.

Larry/Lena
Hobo KK42
Melaque, Jalisco, MX

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.

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.**

Click to expand...

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.



*

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.

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

GonzoF1 wrote:... I am going to change the filter FIRST

Click to expand...

I'm betting that the filter is the culprit.

*