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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


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Old 08-13-2014
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Engine diagnosis Yanmar 7.5 hp...

I am taking possession of a 1983 Cal 27 and the motor has issues. I haven't personally tried running it yet, but a friend of the previous owner was telling me the following...
The boat has sat for the last 11 months without being run.
Last time they were out on it the motor was having what he thinks are fuel related issues. It would start up run for a couple minutes then die.
They would crank it over a couple times and it would start, run for a minute or two then die again.

My thought is that a fuel pump is not providing enough pressure to keep up with demand?
Maybe a clogged fuel filter?

How long can diesel fuel sit before going bad?
Best way to evacuate the existing fuel?

Any help is appreciated.
Zac
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Old 08-13-2014
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Re: Engine diagnosis Yanmar 7.5 hp...

Sounds like air is making its way into the fuel system.

Would start by checking for leaks in the fuel system and tighten fittings. Change all the fuel filters, pick up tube, etc. Might pump out and inspect diesel tank and start with fresh/clean fuel

Josh
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Re: Engine diagnosis Yanmar 7.5 hp...

to test system by pass using a bottle if clean fresh fuel with hose attached....if it does better and runs fine then that means you have leaks before the internal fuel filter banjo fitting before the high pressure tubing

if it still does it it means you mught have issues with the fittings at the injector(s)

if you still have issues after eliminating all possible sources of leaks(by passing fuel tank, extrenal fuel filter etc) look at the fuel pump, and diaphragm
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Re: Engine diagnosis Yanmar 7.5 hp...

Thanks for the help.

So if there is a loose connection or crack in a fuel line between the fuel tank and the motor this would cause the motor to act like this?

I am really uneasy about 11 month+ old diesel that has been sitting inside the motor. Is there a way to bleed that old fuel out without running it through the fuel filter and injector?

Another question I have is on the raw water intake...
I have read that if the motor is hard to start the water intake valve should be closed until after the motor starts.

Is this correct?
Would this cause damage to the impeller by not having water supply?
Or is it a different type of impeller than what is inside an outboard motor?
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Re: Engine diagnosis Yanmar 7.5 hp...

the reason they say that is so your not running water through the engine for minutes at a time where its possible to get water in...

having said that max cranking times should never exceed 30 seconds...as it will damage the starter motor and overheat the wires on most any engine, especially diesels with their high comps to turn over

regarding the old fuel use a manual or electric pump and pump it out of he tank

rinse with fresh fuel a galon or so, pump out again...

dump a can of seafoam in tank then fill her up...this is good enough for most any tank that isnt completely trashed and old.

now

yes any crack anywhere in the fuel system is enough to hiccup a diesel, when there are more than one crack or a really bad fitting or loose banjo bolt etc the diesel will simply stall out and not start again.

sometimes you get lucky with a seal on the bottom of the racor fuel filter if you have one or something like that

but a new to you engine with unknown maintenance best just bite the bullet and get a good fuel filter(water separator if you have the change) new hoses and clamps, as well as new crush washers for all banjo fittings...

peace
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Re: Engine diagnosis Yanmar 7.5 hp...

You may also want to check the tank vent or just run it with the filler cap off. I have read where the screen on the pick up tube, if there is one, in the tank gets plugged or picks up debris. The items that other posters mentioned are probably more likely to be causing the problem?

Paul T
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Old 08-14-2014
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Re: Engine diagnosis Yanmar 7.5 hp...

Lots of good suggestions above. Definitely sounds like either air in the fuel or fuel starvation. Just go after it one item at a time until you find what's causing the problem. Certainly starting by changing the fuel filter and fresh fuel makes sense. And no need to close the water intake unless the engine doesn't start right away. If it doesn't start, excessive cranking can cause water to back up in the exhaust system into the engine.
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Last edited by JimsCAL; 08-15-2014 at 07:59 AM.
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Old 08-14-2014
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Re: Engine diagnosis Yanmar 7.5 hp...

I think your gut feeling is correct. Buy some more fuel and a fuel stabilizer and put it in the tank. You don't mention the engine, but if it's a Yanmar, on top of the valve cover is a compression lever. Have someone pull it up, Remove the air cleaner and squirt WD40 directly into the engine while you are cranking.

It should at least sputter or even start.

If that doesn't do it remove the valve cover, there will be two valves and I recommend you adjust them.

If it's a Yanmar diesel and you don't have it, there's a place to download the complete Yanmar engine manual here

http://www.catamaransite.com/engine.html
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Re: Engine diagnosis Yanmar 7.5 hp...

Thanks again for all the help. I am going to download that service manual but it appears to be for the newer 1GM10 motors and I am pretty sure my 1983 motor is a 1GM...Does that make a difference in the specification on valve adjustments? I would hate to adjust it incorrectly.

Next is onto the fuel system. I need to get the boat up and running right away and remove it from the sellers dock. This means I will not be able to take much time tinkering with one by one fuel system repairs. I was going to do the following...
Bring a can of new diesel with me, and enough flexible fuel line to connect the fuel can as close to the fuel pump as possible. I do not know the model or type of external fuel filter installed currently, so I was going to use a large lawn mower fuel filter attached inside the fuel can to make sure no deposits make it into the injectors.

Then once I have the boat moored at it's new home I can start troubleshooting the existing fuel system. Do you guys think this is a good idea? The motoring trip from the existing dock, until I at least clear the bridges in the downtown area, will be roughly 1 hr so it doesn't have to run for too long. I am guessing 3 gallons should be plenty? Also I should use automotive diesel correct because it is of higher quality?

Thanks again,
Zac
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Re: Engine diagnosis Yanmar 7.5 hp...

The diesel in your tank will not go off in 11 months. But you can have a bug which grows and shows up as black gunge on your filter.

Why no borrow a outboard gas tank and fill that with diesel and gravity feed that engine.

When you are moving your boat make sure you can drop your anchor at a moments notice.

If you have a dinghy with an outboard be aware that even an 2 hp eggbeater will move you along just fine along as it is not a big head wind. Practice rigging for a hip tow and leave the lines attached.
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