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jfmid 06-08-2010 03:53 PM

Diesel Stalls at Idle
Hello all,
New to site so bear with me if I dont get everything perfect.

My O'day 272LE has a 10 hp inboard Universal Diesel. I had to transport her down from Rhode Island to Barnegat Bay, NJ and did the trip by mostly motoring as there were long stretches with no wind. We ran at about 5 knots and made decent time but it was a long slow trip. There is no RPM guage and just a Temp guage and it was pegged at 185 the whole trip so cooling seemed good. Before the trip we changed all filters and oil so everything was fresh.
At the very end of the third day I got some air into the lines as I allowed her to run out of fuel. (there is no fuel guage and it seems that it used more than I thought it would on a long stretch) I'll be more careful in the future.

I was unable to restart it not knowing that the air in lines prevents proper fuel pattern. Now I know. I got it to a marina where a diesel mechanic bled the lines, replaced filters, and got it running again. Also replaced leaking exhaust water hose and did a tune up adjusting valves, changing impeller, changed oil, and filters.
Bottom line is that on the final leg of the voyage she stalled at a low idle while I was refueling after running for a while. Does the diesel have to be turned off to refuel???
I was able to restart and ran well just until I pulled into lagoon where we would be docking. Of course just when I needed to go to low idle and maneuver in tight quarters it quit and wouldn't restart. Luckily I was able to drift and steer and avoided slamming into other docks and boats and was able to secure to my dock and catch my breath. After a few hours of mental stabilization I was puttering around on the boat and restarted the diesel and it idled just fine.

I am concerned now that I cant trust the diesel in a low idle situation. I wonder what steps to take to ensure that it is working well. Is it a factor of being run for a long period of time??? This doesn't make sense to me as diesel trucks run for hours and hours and dont stall as they come up to a stop light but maybe small marine diesels are a completely different animal. Do I just increase the idle speed by approx 100rpm? Again no RPM guage so kinda hard to tell what the RPM's are. The mechanic who worked on it will be able to come to my dock and take a look but I want to have an idea of what is going on.
Thanks in advance for any input and suggestions.

Faster 06-08-2010 04:57 PM

Does it idle OK in neutral? and die when it's put into gear? The simple fix to try is to indeed raise the idle speed until that no longer happens.

However, if you're using excessive fuel, that, coupled with your other symptoms (ie slowish motoring speed) may mean your prop is too big a pitch as well.

Gene T 06-08-2010 05:57 PM

My first impression is a plugged fuel filter. You used the boat a lot and could have stirred up dirt in the tank. A filter can plug quickly causing a high vacuum in the fuel lines and fuel bowl. The fuel bowl has o-ring seals that can leak air in the system when the vacuum gets too high. So I would check the filters first. If dirty you should look into cleaning the fuel tank.

I believe you should have a working tachometer.
I also like having a vacuum guage after the filter. It is a fast way to isolate a problem with the engine.


jfmid 06-08-2010 07:06 PM

I definately want a working tach. I will check the fuel filters to see if they are dirty. They werent when I changed them myself right after the diesel died on the third day. Then the mechanic changed them again. So that is 3 new sets of fuel filters. If they are dirty when I check them now it must mean that the fuel tank is messy and will need to be cleaned.
3 questions.
how to add a tach??
How to clean fuel tank?? ( is that a job for a marina??)
what is and how to add a vacuum guage after the primary filter??

Gene T 06-08-2010 07:49 PM

My last boat had a problem with the pickup tube in the tank. A piece of crud came loose and would drift around the bottom until an inopportune time. When I would shut of the engine the vacuum would drop and the piece would drift free and the engine would start and run fine. The crud was a mat like substance that had built up from the dead critters that live in the diesel. I cleaned the tank myself. I used an outboard bulb as a pump and some copper tubing to scrape the crud loose and suck it up. I used old t shirts to filter out the crud as I filled gallon jugs. I then poured the filtered diesel back in the tank through more t shirts. A messy job that took several hours but it solved my problem.

Tach - Either the engine manufacturer or you could probably run one off the alternator - you would need to calibrate it.

Vacuum gauge. Any marine store should have one. If you hunt around you can find better pricing.



SteveInMD 06-08-2010 07:59 PM

A clogged filter or pickup would give you low power a cruising speed. You are less likely to notice it at idle. It sounds to me like you have a classic air leak. With all the work you've done on the motor it's probably just a filter or connection that's not quite tight. Go over the system and check each connection.

No, you don't have to shut off the motor to refuel.

jrd22 06-08-2010 10:40 PM

I agree with Steve above that you would normally have problems at high load/rpm if it was a clogged filter. I would check the idle rpm (when hot)with a handheld tach and if it is below manufacturer's specs adjust it up. It could be that you have some air still in the system or a small air leak as Steve said. With the engine idling crack open one the line to an injector (do them all), if you see any air bubbles you have air getting in somewhere.

bfloyd825 06-09-2010 06:03 PM

Check for a fuel leak as others have mentioned. Also, the idle may be set a tad too low as well.

Northeaster 06-09-2010 08:11 PM

Try finding a manual for your engine (perhaps on-line). That will tell you whether your engine would normally have come with a tach, and what type of sensor. I am no mechanic, but some work off of the alternator, others by counting teeth on the flywheel / magetic pickup, etc .
My Yanmar had no tach, but did have the magnetic pickup tach sensor to count teeth, so I just had to buy the appropriate type of tach. I bought a Faria tach made for diesels (had appropriate rpm range)

here are two different types:

capcass 06-17-2010 12:28 PM

Similiar problem Yanmar 2gm
I have a 1980 Yanmar 2Gm installed on my 30ft sailboat. It runs fine at all rpms, except below 1100 when it stalls. I've changed the injectors, filters and bled the system withtout any remedy. The lift pump was replaced last year. Any suggestion as to what to check next (i.e injector pump timing, compression, valve adjustment, etc.) ? I am prepared to bring in a diesel mechanic, but would like to know that he is following the right diagnostic process rather that just changing parts. Any suggestion on what may be the most likely cause of this low idle stalling condition for this engine would be greatly appreciated.
Gary Cassidy, USCG Master

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