Chris W replaced his Onan with a Phasor.  Boy that would be nice.  John Even had his electrical end rebuilt which includes hard to find parts and service for.  My issue is not the electrical side.  On the way up the unit was running great.  It was not running fast enough on the first leg of our trip from FL to MI so in Mobile the mechanic bumped it up to 1800rpm.  Ran great from Mobile to Lake Barkley.  On the last leg south of STL it started to show signs of trouble.  Start, run a while, sputter and die.  After a couple more instances we shut it down permanently and went old school the rest of way.  I finally tried to start it in MI and blue/white smoke everywhere.  Verdict was injectors.  Replaced those and it ran good, no oil burn or smoke,  but we really didn't use it because the mechanic wanted to adjust the valves.  Now it runs but burns oil putting a sheen on the water and smokes a bit.  A case of maybe leaving alone.  The question becomes why.  Valve grind?  Compression is not at spec but equal in all and not far enough off to cause much of an issue.  So says me, a guy who knows enough to be dangerous on the subject.  Hopefully some work on the valves will take care if the issue.  My mechanic is old school and has the same genset.  He works on all types of diesels, including antique tractors, marine, truck .... so he is well versed and not afraid of old crap.  Since when did 40 years become obsolete?  

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Mike, the question I can answer about obsolescence is when it changes.  40 years old is obsolete until one reaches some age around 35 then it is only old, at 50 one may consider it to be proven.  At my age I consider my Kohler to be proven and reliable!  

Tim, the ancient

Mike,

I'm going to make some comments based only on what you have posted here. Since I have not seen nor heard your generator run and do not know the complete history and hours on the engine, my comments are some what limited by this.

You stated:

1) That the generator ran fine at the beginning

2)  Then had problems with maintaining proper rpm

3) A mechanic adjusted the rpm.

5) Generator than ran fine for awhile

6) The generator started to sputter and die after a period of time

7) You gave up on it until getting back to Michigan

8) You got it to run again but with blue/white smoke

9) Your mechanic then determined that the engine needed injectors which were replaced.

10) Compression is not at spec but close.

11) Now it is putting a sheen on the water and you are stating that it burns oil.

12) You are considering a valve job now.

Steps 1-8 are screaming clogged fuel filters, bad fuel, an air leak or all the above. You never mentioned if both fuel filters were replaced and with what. When a diesel starts to suffer from fuel starvation, the first thing that will happen is that the horsepower will drop off which often means that it won't maintain rated rpm. The sputtering and dying is definitely a fuel starvation symptom.

Did the boat engines have fuel issues at the same time? Does the boat have a separate fuel tank for the generator?

You also did not state what the compression was in psi. What is it exactly? Does the engine start easily? How many hours are on the hour meter?

Why I ask all of these questions is that from the initial condition, the generator seems to be fine. Injectors do not go suddenly bad unless you run a bunch of water through them.

The oil sheen that you are seeing on the water is very likely unburned diesel fuel. You say that it is burning oil. Is it actually consuming oil or is it because you see some blue smoke?

The Ambac PSU injection pumps have some unique design features. The biggest difference is that the pump uses an external governor. This feature makes troubleshooting the injection system a little different in that on other injection pumps with the internal governors, low fuel pressure will cause the governor to flutter since they are usually hydraulic. Since the PSU does not have the internal governor, some fuel issues are masked.

There is an external transfer pump that feeds the injection pump. The injection pump must be supplied with fuel at 12-14psi for the injection pump to operate correctly. You should verify this with the generator preferably at full load with a pressure gauge

There is a fuel return from the injectors and injection pump that must have an unobstructed flow back to the fuel tank. If this line is turned off or clogged, air bubbles from the injector caused by combustion pressure at the injector will eventually get trapped in the injection pump and cause it not to operate correctly.

There is a brass fitting on the side of the injection pump that the injector return lines go to and the tank return line starts from. The brass fitting has a poppet valve inside it which limits the fuel pressure delivered by the transfer pump. This fitting must be present and the poppet valve intact for the fuel injection system to operate correctly.

If this boat sat for awhile (a long time) and if the fuel tanks were not polished, it is likely that you have some fuel issues. Since the generator engine is fairly small and does not have a lot of fuel filter area, it is much more sensitive to clogged fuel filter issues. One of the most insidious problems  is when the final fuel filter starts to blind off. The engine will run and then die. If the engine sets for a while, the filter element recovers somewhat and then the engine will run fine for a while before acting up again. Very puzzling unless you understand what is happening.

There is also the issue of the injection pump timing. The Ambac PSU pump uses a timing button that comes in various lengths to set the pump timing. Before I would take anything apart on the engine, I would verify that the pump timing is correct.

The Onan diesel engine uses a precombustion chamber head design. When the compression starts to go away on these engines, they will become extremely difficult to start.

Care needs to be exercised when interpreting smoke color on a diesel engines  as the context of the other associated symptoms should be applied.

White smoke usually means that you have no or very poor combustion. This can be caused by low cylinder temperature, low compression, late injection timing, a bad injector nozzle, and low injector pressure.

Blue smoke can be caused by oil through the valve guides or rings. This is actually fairly rare in a diesel engine and the blue smoke is more frequently actually caused by low engine combustion temperature. Stale fuel and insufficient injection system fuel pressure is often the primary cause of this symptom.

The main reason why blue smoke in a diesel is usually not oil is that a diesel engine runs at close to zero intake vacuum. This means that there is very little suction to draw oil through the valve guides and or rings. This is quite the opposite of a gas engine which usually will be around 15in.of vacuum unless at WOT. Unless the diesel engine is actually consuming a significant amount of oil like X number of pints per Y hours, I would be looking at other things first.

A lot of diesel injectors get replaced needlessly because of poor understanding of the particular injection system that is being investigated. The Ambac PSU system requires that the injector have a 2100psi cracking pressure at the injector. The injection pump will have a normal pressure of around 1400psi before the injection cycle starts. What this means is that unless you have proper fuel pressures on both sides of the injection  pump, the injectors will not function correctly. This means that many times injectors are often misdiagnosed because of other issues. A systematic approach to troubleshooting and diagnosis is imperative to avoid these pitfalls. A common symptom is blue smoke from low injector pressure.

Most of this information can be gleaned from studying the Onan generator manual which happens to be in the files section here.

Ron,

Thank you for your thoughts and a detailed response.  I've found your previous responses to others to be the same.  The knowledge on this and other sites is impressive.  I'll try to respond as best I can but my mechanical knowledge is limited.  This will be very helpful when working with my mechanic.  Especially when it comes to diesels as I have always had gas. My notes are below your bullet points.

Ronald Zick said:

Mike,

I'm going to make some comments based only on what you have posted here. Since I have not seen nor heard your generator run and do not know the complete history and hours on the engine, my comments are some what limited by this.

You stated:

1) That the generator ran fine at the beginning.  Started at the dock.  Ran fine.  Did not put a full load on it.

2)  Then had problems with maintaining proper rpm  My guess was it was set too low to start with.  First indication was not enough juice to the microwave when crossing the gulf.  Other than that it ran and started fine.

3) A mechanic adjusted the rpm. Adjusted to 1800 when work was done in Mobile.  All seemed to be fine.

5) Generator than ran fine for awhile.  Ran well from Mobile to Lake Barkley

6) The generator started to sputter and die after a period of time.  Sputtered  and died one morning on the way up the MS.  I want to say it was the start of the third day.

7) You gave up on it until getting back to Michigan. Ran it a few times.  Got worse and shut it down.

8) You got it to run again but with blue/white smoke.  Next start was in MI after a week or two.  Frankly, after 2000 miles she became a dock queen for a bit.

9) Your mechanic then determined that the engine needed injectors which were replaced. First we replaced the fuel filters.

10) Compression is not at spec but close. If I recall correctly he said it was at 230psi

11) Now it is putting a sheen on the water and you are stating that it burns oil.

12) You are considering a valve job now. Valves were adjusted.  then it smoked more. prior to the adjustment it seemed fine.

Steps 1-8 are screaming clogged fuel filters, bad fuel, an air leak or all the above. You never mentioned if both fuel filters were replaced and with what. When a diesel starts to suffer from fuel starvation, the first thing that will happen is that the horsepower will drop off which often means that it won't maintain rated rpm. The sputtering and dying is definitely a fuel starvation symptom.  First thought was fuel starvation. 

Did the boat engines have fuel issues at the same time? Does the boat have a separate fuel tank for the generator?  No issues with fuel.  My guess is we used close to 3000 or more gallons the entire trip with no issue.  Gen runs off the starboard tank.

You also did not state what the compression was in psi. What is it exactly? Does the engine start easily? How many hours are on the hour meter? It was starting fine at any point in time.  Now it won't start from the remote switch which came on suddenly.  Could be a switch or wire.  Don't recall the hours or trust the gauges.

Why I ask all of these questions is that from the initial condition, the generator seems to be fine. Injectors do not go suddenly bad unless you run a bunch of water through them.

The oil sheen that you are seeing on the water is very likely unburned diesel fuel. You say that it is burning oil. Is it actually consuming oil or is it because you see some blue smoke? Haven't run it enough to make that call.  

The Ambac PSU injection pumps have some unique design features. The biggest difference is that the pump uses an external governor. This feature makes troubleshooting the injection system a little different in that on other injection pumps with the internal governors, low fuel pressure will cause the governor to flutter since they are usually hydraulic. Since the PSU does not have the internal governor, some fuel issues are masked.

There is an external transfer pump that feeds the injection pump. The injection pump must be supplied with fuel at 12-14psi for the injection pump to operate correctly. You should verify this with the generator preferably at full load with a pressure gauge

There is a fuel return from the injectors and injection pump that must have an unobstructed flow back to the fuel tank. If this line is turned off or clogged, air bubbles from the injector caused by combustion pressure at the injector will eventually get trapped in the injection pump and cause it not to operate correctly.

There is a brass fitting on the side of the injection pump that the injector return lines go to and the tank return line starts from. The brass fitting has a poppet valve inside it which limits the fuel pressure delivered by the transfer pump. This fitting must be present and the poppet valve intact for the fuel injection system to operate correctly.

If this boat sat for awhile (a long time) and if the fuel tanks were not polished, it is likely that you have some fuel issues. Since the generator engine is fairly small and does not have a lot of fuel filter area, it is much more sensitive to clogged fuel filter issues. One of the most insidious problems  is when the final fuel filter starts to blind off. The engine will run and then die. If the engine sets for a while, the filter element recovers somewhat and then the engine will run fine for a while before acting up again. Very puzzling unless you understand what is happening.

There is also the issue of the injection pump timing. The Ambac PSU pump uses a timing button that comes in various lengths to set the pump timing. Before I would take anything apart on the engine, I would verify that the pump timing is correct.

The Onan diesel engine uses a precombustion chamber head design. When the compression starts to go away on these engines, they will become extremely difficult to start.

Care needs to be exercised when interpreting smoke color on a diesel engines  as the context of the other associated symptoms should be applied.

White smoke usually means that you have no or very poor combustion. This can be caused by low cylinder temperature, low compression, late injection timing, a bad injector nozzle, and low injector pressure.

Blue smoke can be caused by oil through the valve guides or rings. This is actually fairly rare in a diesel engine and the blue smoke is more frequently actually caused by low engine combustion temperature. Stale fuel and insufficient injection system fuel pressure is often the primary cause of this symptom.

The main reason why blue smoke in a diesel is usually not oil is that a diesel engine runs at close to zero intake vacuum. This means that there is very little suction to draw oil through the valve guides and or rings. This is quite the opposite of a gas engine which usually will be around 15in.of vacuum unless at WOT. Unless the diesel engine is actually consuming a significant amount of oil like X number of pints per Y hours, I would be looking at other things first.

A lot of diesel injectors get replaced needlessly because of poor understanding of the particular injection system that is being investigated. The Ambac PSU system requires that the injector have a 2100psi cracking pressure at the injector. The injection pump will have a normal pressure of around 1400psi before the injection cycle starts. What this means is that unless you have proper fuel pressures on both sides of the injection  pump, the injectors will not function correctly. This means that many times injectors are often misdiagnosed because of other issues. A systematic approach to troubleshooting and diagnosis is imperative to avoid these pitfalls. A common symptom is blue smoke from low injector pressure.

Most of this information can be gleaned from studying the Onan generator manual which happens to be in the files section here. Most of the above is beyond my comprehension and will pass it on or study some more.  When laying up the boat for the winter I did find an insidious slow drip at the fuel supply shut off valve where it comes out of the tank.  I could see it was leaking for a who knows how long and I would get whiffs of fuel smell in the stateroom.  I've shut that off as it was leaking even at rest.  Hopefully just packing as it is a standard hose bib.  

Thanks again,

Mike

Holy cow Ron. I don't even have a diesel generator and I was fascinated by the precise description you gave about possible /probable troubles with his genny. I am so thankful that there are such informed persons on here that share their knowledge and experience to help other navigate through some of boatings landmines. I know I have saved a small fortune over the years with some of the advice I have received on here. Well done!! 

Sounds like you may have found the problem . If it's leaking fuel it probably is leaking air into the system when it's under suction when the unit is running . Anyway I would sure fix that first .

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