Yanmar 1GM10 loses power, please help

[jimczarnowski]

Hi all. This looks like the right place to ask this question..

I have a 1GM10 that has been well maintained in my Ericson 26, but on a recent trip back from Catalina, where it ran at smoothly at 2900 RMP for 20 hrs, it suddenly dropped to 2000. I replaced both fuel filters, the air filter and checked the intake in tank for clogs. All was pretty clean. Next, I re-primed and that seemed to fix it for a few hours. But then, drop to 2000 max RPM, and running rough, like it was fuel starved. I have re-primed a couple more times with the same results. Any chance it is my fuel pump? Or air getting into the line? I do recall bubbles coming out when I primed. I also cracked the nut at the injector and turned the engine over by hand (with the decompression lever pressed) to bleed that section of fuel line. I was surprised to not see much fuel pumping out around this nut. Should it bleed like the normal bleed screw when the manual fuel pump is actuated? Thanks!

[sailorchic34]

Originally Posted by jimczarnowski

Should it bleed like the normal bleed screw when the manual fuel pump is actuated? Thanks!

The lift pump will not pump past the injector pump, only up to it. Me I prime the system up to the lift pump. Then crack open the lines at the injector, pull the decompression lever(s) and push the start button for 15 seconds or so. close the nuts and tray starting. If it does not start repeat the last bit.

On mine it takes three or four attempts at bleeding to get it where it starts.

It might be a clog at the fuel pick up/ dip tube, a vacuum leak or weak lift pump.

[jimczarnowski]

Thanks for that advice on priming. It is strange, it never has trouble starting, but it will do the thing where it will run great at full power for several hours and then just wind down to 2000 RPM max and run rough. Re-priming seems to fix it temporarily...

[Rocketman]

Sounds like a tinny air leak somewhere. Check all, and I mean all the fuel lines and conections, filters all the way back to the fuel tank, and if you have the ability check the fuel pickup inside the tank.

I had a simular problem that presented itself every time I went to start the engine. I had to reprime everytime I used the engine. I finally found a tinny air leak between the fuel pump and fuel filter. It was so frustrating it took me weeks to find it, but once I did all it took was a quarter turn of a nut and it was fixed.

[Neo]

Would you experience the same power loss the next day on start up if you didn't re-prime? If not, then it probably is not air in the line.

I very little experience with diesel engines, but based on what I've read I would try to rule out the following first:

1. Floating debris in fuel tank blocking pick up. I have heard people suggest putting the fuel line (coming from the fuel tank) into a clean jug of fuel to see if you still lose power.

2. Fuel tank vent clogged creating vacuum in fuel tank. Blow out the vent line.

[jimczarnowski]

The power drop seems to occur after the engine is running for a while. It will always start up right away, but just won't rev past 2000. Before the long trip to catalina, I pulled the fuel tank, scrubbed it clean and put all back together. All of the fuel lines were disconnected and I reconnected them with double hose clamps. I will go through the lines again an look for a small leak.

[Neo]

So, after you restart the engine the next day (without re-priming the system), you can get the revs above 2000 for the first two hours, then it bogs down?

Or is it since catalina, you can never get the revs above 2000?

Like I said, I don't know squat, but according to the 1GM shop manual the problem does not seem to be air in the line since your engine is not misfiring.
You may have stirred up sediment in your tank when you cleaned it.

3. Engine speed decreases unexpectedly-Check for water
in the fuel. Check for a cloggeq fuel filter element.
Bleed the fuel system as described in Chapter Seven to remove
air in the fuel. Check for clogged or defective fuel
injection pump or fuel injector.
4. Engine will not run under full load-Check for a
clogged fuel filter element. Check for a defective fuel
transfer pump. Check for a clogged or defective fuel injection
pump. Check the speed control mechanism.

5. Engine misfires-Check for water in the fuel. Check
for a clogged fuel filter element. Bleed the fuel system as
described in Chapter Seven to remove air in fuel. Check
for a clogged or defective fuel injection pump or fuel injector.

[Neo]

I have a pdf copy of the manual if you need it.

[Rocketman]

You mentioned a couple of things that seem like air in the system.

1. Tinny air bubbles when you primed it. There should not be any air bubbles.

2. Runs great after primming then misses and will not develop full power.

A couple of other questions.

1. You say is always starts right up. Do you have to prime it to get it started?

2. Will it start up and run fine if you shut it down when it is running poorly?

Someone has mentioned it already but your vent or vent tube may be cloged or kinked not alowing enough air to enter the tank as fuel is used creating a vaccum.

A lift pump is unlikely as you normaly would not see periods of unexplained improvements.

[jimczarnowski]

Neo, thanks for offering but I have a copy of the service manual.

Answers for you, Rocketman:

1. You say is always starts right up. Do you have to prime it to get it started?

no prime required for starting, it will always start right away, just doesn't develop full power

2. Will it start up and run fine if you shut it down when it is running poorly?

This was the case last time. It was running poorly, put it away, couple weeks later, started and ran fine for a few hours... sounds like vent tube restriction/vacuum possibly, but that wouldn't explain perfect 30 hrs of running to/from catalina followed by trouble. Air in line maybe maybe more likely. This seems more likely to have developed over a long run / vibration period and could explain the apparent spontaneity of the problem.

Thanks

[YankeePSC34]

You may check the fuel line for cracks. Take the hose off the tank fitting. Block it with the shaft of a drill and a hose clamp air tight. Then take the hose off the fuel pump or the primary filter. Use a fender pump or similar to create over pressure in the fuel hose. If the hose holds the pressure, what you can feel at the pump, check next the pick up pipe in the fuel tank for pin holes using the same pressurizing method.
As you said it could be also a tank aeration problem.
My guess is that debris is floating around in the tank and occasionally it will partially block the tank pick up pipe.

[jimczarnowski]

I worked on the engine for quite a while today. I put a new fuel tank in and new fuel and changed both filters. I also flushed all of the old fuel out of the filters and lines and pressure tested the whole fuel line system to 20 PSI - no leaks. Now the engine is slightly improved, no longer stalls at 2000 RPMs, but it still runs rough as it approaches 3000 RPMs. Then it will continue to fluctuate between 2500 RPMs and 2800 RPMs. I am at a loss. Should I consider the fuel injection pump? if it were a gas engine, I would say it just needs to have its needle valve air fuel mixture adjusted. I am relatively new to diesels and so I don't know how to deal with the rough high-end running of the engine. Any ideas?

[YankeePSC34]

I would focus on the governor next. That's the device designed for controlling the revs.

[Rakuflames]

Originally Posted by jimczarnowski

Hi all. This looks like the right place to ask this question..

I have a 1GM10 that has been well maintained in my Ericson 26, but on a recent trip back from Catalina, where it ran at smoothly at 2900 RMP for 20 hrs, it suddenly dropped to 2000. I replaced both fuel filters, the air filter and checked the intake in tank for clogs. All was pretty clean. Next, I re-primed and that seemed to fix it for a few hours. But then, drop to 2000 max RPM, and running rough, like it was fuel starved. I have re-primed a couple more times with the same results. Any chance it is my fuel pump? Or air getting into the line? I do recall bubbles coming out when I primed. I also cracked the nut at the injector and turned the engine over by hand (with the decompression lever pressed) to bleed that section of fuel line. I was surprised to not see much fuel pumping out around this nut. Should it bleed like the normal bleed screw when the manual fuel pump is actuated? Thanks!

Are you certain you don't have a dirty fuel tank?

[jimczarnowski]

New fuel, new fuel tank, new filters. Fuel is as good as it will get. Maybe there is some pump / injector treatment I can run through it? How do I go about adjusting the governor?

Thanks