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Yanmar 2GM20F stalling problem.

prjacobs

New member
Background:
The engine is a Yanmar 2GMF20 with about 2500 hours. During a 26 month re-fit on the boat (150 engine hours ago) the following was done: All new fuel system, filters, and lines, tank boiled out, new filler hose and vent.
The engine ran perfectly for 150 hours before displaying stalling symptoms. All filters were changed and the system bled as per the manual.
I still have a problem.
From a cold engine the following happens:
Fires up easily and idles smoothly.
In gear and up to cruising rpm ... smooth and lots of power.
After 5 to 7 minutes engine starts to loose rpm and then stalls.
After immediate re-starting will not idle without some additional throttle, and needs full throttle to push the prop.
Leave it for an hour or two and the whole process repeats, but only runs about 5 minutes.

It feels like a fuel starvation problem. The only hose that has never been replaced is the one between the engine filter and the injector pump. I´ve ordered a new one and also a new lift pump, although the existing lift pump seems to work perfectly.

Other checks I´ve made are:
Fuel tank pickup and line: clear.
Fuel return line: clear and plumbed into top of tank.
Tank vent and hose: clear
Lift pump primer lever: working well.

As it runs so well at first I don´t suspect the injector pump, but I´ve run out of ideas.

Any and all help greatly appreciated!
Peter.
 
Sounds like a starvation issue. try running it off a portable fuel tank and see if it resolves the issue, if it does you know everything on the engine is good.
 
Thanks for the suggestion. I did try running it from a portable tank direct to the inlet on the injection pump. Again, it ran well at first, then started to loose RPM. Squeezing the bulb on the tank every 10 seconds would get the engine up to RPM again. And again, it didn't do this until it had warmed up.
I've removed the injector pump and sent it in for testing.
Meanwhile I've removed the tank pickup tube and the primary filter housing and tested them with a vacuum pump ... both passed. I also installed a new engine secondary filter housing as the bleed screws on the old one may be suspect. Maybe air is still getting in somewhere, although I can't find any leaks. As a last ditch effort I'll temporarily substitute clear vinyl tubing for the rubber fuel lines and see if any bubbles appear anywhere.
Peter.
 
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Good thought, but definatley not the case as I can lay a hand on any part of the engine without getting burned. Will pull the thermostat and give it the hot water test anyway, just to be sure.
Thanks.
Peter.
 
A brief note to thank you for all the help and suggestions for my ailing Yanmar 2GH20F Diesel engine in my boat.
It took me a month, but eventually I think I've nailed the problem, which was air getting into the fuel system, and after 1/2 hour of running, causing it to stall.

There's a steel fuel line between the lift pump and the engine fuel filter. It has 'banjo' fittings on either end that are sealed with copper crush washers. To prevent vibration in the line there's a small 'U' clip mid way that straps the line to the heat exchanger casting. Rust had formed under the clip and eaten into the line. Although careful inspection failed to reveal a leak, I did solder up a couple of the larger rust craters.

I suspect the line, being strapped to the heat exchanger, took about 30 minutes to heat up and expand enough to let in a small amount of air. The fact that the line is on the pressure side of the lift pump suggests an outward leak rather than air being sucked in, but sometimes the universe works in mysterious ways ... I'm good with that.

This repair, plus a complete replacement of suspect fuel with good Canadian Diesel, has solved the problem. An extended trip under power has restored my faith in engine.

The only thing left to do is aquire a new fuel line to replace the repaired one.
 
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