low rpm's on Yanmar 1GM

[RAC]

Last spring the first 4-5 times out, the Yanmar 1GM would not run higher than 2200-2500 rpms. This was after the marina winterized and changed all the fuel filters the previous fall. Others speculated it was growth on hull and prop. after a few times out it just started running about 3200 rpms and worked fine all last season.
near the end of the season last fal 2011l, the service guy at the marina went ahead and changed the oil and the fuel filters, but before he winterized the engine, so i took it out a couple of times before we buttoned it up for the winter. what happened again was it would not run faster then 2200-2400 rpms.

In 2010 the PO Documented following repairs. drain,clean and flush fuel tank. removed inj pump and nozzle, clean and check nozzle, disassemble clean and rebuild injector pump.
it ran fine the summer and fall of 2010 and other then the first few times out it ran fine all of 2011 until the fuel filter change in October 2011.

It seems like it is not getting all the fuel it needs when this low rpm condition occurs. could there be something in the pickup tube in the fuel tank that is restricting fuel flow. i understand if the fuel lines needed bleeding, it would not run at all... is that correct? Since the injector repairs in 2010, we have only run about 10 gallons of fuel through it if that much.

it just seems odd that each time the fuel filters were changed, we had this problem. Has anyone had a similar problem with this one banger? Thanks for your help. Alan

 

[Steve Dion]

Alan: It is not uncommon to have issues with the pick up tube in the tank. I would suggest that you remove this and see if there is a screen. If there is you may want to remove it and see if that helps. There may be something in the tank that is partially blocking your fuel delivery.

 

[Robert 47]

You might also check and see what kind of fuel filter the yard is putting on your engine, and if the mechanic is bleeding it out properly. Yanmar's might be picky on the proper fuel filter. Check your fuel lines to see if they are not collapsing. Other thank what Steve has suggested, the only other suggestion is a new air filter. Marine diesel engines are like most any other diesel engine, clean fuel, clean filters, i.e. (fuel, air, oil), you shouldn't have any problems.
Do you have a primary and a secondary fuel filter system?
I know of at least 3 boats in my harbor that I have had to help service due to "rotten" fuel, and old dirty filters.

If you decide to clean out the fuel tank, I suggest using "SeaFoam", does an excellant job of cleaning.

 

[RAC]

thanks for the replies.... yes, we have the two filter system, they used the Yanmar and Racor filters, and the air filter was just replaced. The yard service guy thought it might be a fuel pump going bad. just seemed odd that i had the same condition after new fuel filters were installed. in a few weeks we will be able to open it up for spring and i can check this out. Last spring it after running a few times it just started running better. Go figure??? thanks again, Alan

 

[Benny17441]

How are you measuring RPM? Tachometers are known to provide incorrect readings from time to time due to corroded connectors or dirty pick-up sensors. There should be a corresponding loss of speed with a reduction in actual engine RPM. Bad fuel or a clogged exhaust mixing elbow can be a possibility for loss of RPM.

 

[RAC]

measured the rpm's with the tach, but also lost 1-1.5 knots in speed through the water and the engine just didn't sound like it was "giving it's all"... in another 30 days or so we will fire it up for the season and see what happens.... not sure how to check the mixing elbow, will look at possible fuel line collapsing, topped off the fuel tank in Oct so it should be fresh fuel... am i correct that if the lines need bleeding, the engine would not run at all?

 

[Jake N Eggs]

Any time the injection pump is worked on there could be issues created depending on the quality of the work. The fact that it ran well probably discounts the pump but be aware.

The fuel pump compresses the fuel and it is delivered to the injector via a steel line. The injector has a spring holding the injection nozzle closed and when the injection pressure reaches a defined pressure the spring releases and a mist of fuel is sprayed into the cylinder. As the throttle is opened the pump will deliver more fuel and the result is the injector will spray longer at the defined pressure. (This is a little simplified)

If there is a small air bubble trapped in the fuel system which reduces the compressability of the fuel the net result could be a reduction of the fuel spray. A reduction in fuel results in a reduction of engine speed.

With the engine running, quickly loosen and then re-tighten the injector pipe at the pump outlet. Repeat this procedure at the injector. The engine will start to quit when the fitting is loosened so be quick. Also set the throttle at about 1100 rpm when you do this. You may have to repeat the procedure a couple of times.

Be careful of escaping fuel as it is high pressure and will penetrate your skin. Normally there is no danger as the fitting contains the fuel but if you try and hold a rag over the fitting it can be dangerous. Let the fuel run and wipe it up after the fitting is re-tightened.

Good luck and let us know what you find.

 

[RAC]

Thanks!! I will give this a try when we open up for spring.... Alan

 

[Dellcom]

Check the filter, it should be filtering at 10microns...not 2......filtering at 2 microns restricts fuel flow (racor)...check the cable from the the throthle

 

[Dellcom]

Sent by accident...check the cable that controls the engine speed....does it move the arm attached to the engine properly....also there is a crown nut held in place by wire near the levers that control speed and engine shut off....this crown nut controls the rpms and is wired in place .....I do not have the manual with me so I am at a loss for the correct part names..waiting for a root canal......advise if I have confused you or you want more info...all the best

 

[jtm]

RAC- what if you try exclude the tank from the equation by running the engine off an external tank. Just remove the hose and run it into a typical external "tin" tank like you might find on a motor boat. Label the content as DIESEL and Remember to remove the diesel in the "tin" when you are done with the experiment so an not to confuse diesel vs gas content!!!!

If you had exhaust elbow "coking", you'd prolly be unable to get to 3200rpm to any extent/power as you'd likely be constricted and at that rpm backing your exhaust into the engine- and choking down power and rpms.

I think the 5 milicron filter may be a factor.On my external Racor I've used the 10micron for decades without any issues. So leave well enough alone. Also buy your diesel elsewhere and see if there a difference.

 

[Bill Roosa]

I'm thinking that since if fixed itself then the marina worked on it and the problem came back that (duh!) it is something they did incorrectly. The only thing that would fix itself is air somewhere and it eventually escaping resulting in normal RPM.
Jake-N-Eggs annalysis of the injector pump fits that bill as I can't see a filter somehow becoming less clogged "all of a sudden".
It is notoriously hard to get air out of an injector pump BTW, which is why they prime it before they put it back on the motor (or should).

 

[RAC]

Thanks for all the replies.... I get full rpm's in neutral, under a load i loose a little power. i thiink air bubbles, and then working themselves out after the filter change might be the most likely cause. Last time i pumped the little"pump lever thing" on top of the engine, not sure what i was doing, but after awhile of runniing, (motoring out of the marina 3-4 times) it fixed it self. i thought that if i had any air in the lines, it would not run at all.
a couple of more weeks and it should stay warm enough to safely open up for spring. kentucky lake water temp is 47 degrees.
Thanks again! Alan

 

[RAC]

Took Sarayu out for the first sail of the season today. The yanmar 1gm still was running at lower than normal rpms...2200-2300 rpms. ran it about 30 minutes wide open, no change. put it in neutral and opened the engine hatch and tried pumping that lever thing about 200 times. Put it in gear and gave it full throttle and low and behold, went up to 3000 rpms, then slip back to 2500-2800 for a second or two then it loaded up and back to 3000. went back down and pumped the lever thing again another and tried it again. Bam, running 3000-3200... go figure???

 

[jtm]

I'm not familiar with the 1gm- but my last post got me to wondering same possibility on your engine- make sure your compression lever is fully engaged & "cliicked" in place. i figure if it is slightly less than fully engaged, you could lose some power/rpms.