Engine not running stalling at idle when warmed up

Engines, Drive trains, Propellers, Steering, Ground Tackle and other mechanical system
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sailmon
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Joined: Sun Feb 22, 2009 6:53 pm

Engine not running stalling at idle when warmed up

Post by sailmon »

Ok - I need a miracle. Our boat has been in the water for 3 weeks and we haven't been able to leave the dock due to engine problem. Began last season. After long run with engine fully heated up, engine stalled when we pull throttle back to idle. Even if we slow down and cool down a bit before entering dock - stalls as soon as we pull back to idle. Gets a bit hairy entering dock without "brakes". Engine is 1991 vintage Yanmar 3GM30F.

We thought it might be an injector problem so sent them out for cleaning and checkup over winter. Reinstalled and problem persists... Now engine goes rough and stalls at idle after only 1/2 hour run at 2,500 rpm. Have discovered that problem appears to be a small amoun of air accumulating injector pump. Over the past 3 weeks we have replaced the racor filter, then the entire filter assembly, new lift pump, new fuel lines between tank and lift pump, pressure tested fuel system, removed and pressure tested pick-up tube, cleared tank vent, adjusted idle, and did a tribal dance. There are no visible leaks in fuel system.

When engine is running properly (before fully heated up and no air in line), can hit 4,000 rpm no load and 3,400 rpm with load. Can move the boat at 6.7 knots sog. As soon as heated (about 1/2 hour under load) engine begins to misfire.

Finally, we bypassed fuel delivery systems and ran hose from clean tank of fuel directly to lift pump. Ran like a champ... One hour under full load... Throttled back to idle and purred like kitten.

Open to any and all suggestions.
Thank you,
Bob
Sailmon (Captain Bob Allenick)
S/V Her Diamond
1991 Freedom 38
Cleveland, OH

carhelpguy31
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Joined: Wed May 02, 2012 8:04 pm
Location: Flint Mi

Re: Engine not running stalling at idle when warmed up

Post by carhelpguy31 »

Sounds like you have a restrictin in the fuel pick up. When this happens the lift pump sucks so hard it develops air pockets in the fuel, especially under extended heavy load. In your tank do you have a pick up screen on the supply? It may be clogged with dirt or debris. You can tee in a vacuum gauge before or after your Racor and watch the vacum. If it starts going high then there is a restriction. Hope this helps.

Mike
Mike Russell
Bazinga!
Freedom 30/32
Cheboygan, MI.

AlanK
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Joined: Wed Dec 10, 2008 6:59 pm
Location: Freedom 33 Boston, MA USA

Re: Engine not running stalling at idle when warmed up

Post by AlanK »

A few years ago I had a problem (yanmar 3GM) where after warming up the engine would stall under load. Was an air leak but I never identified where. It may have been an air leak at the filter gasket . I was replacing my racor filter system and all lines any way and never had the problem again. I first tried tightening everything (including hose clamps) to no avail.
I have heard of problems when the fuel tank vent line is clogged or the return line is constricted but don't know if the symptoms would match since I've never had that problem.
Alan F-33 1982 Hull 51

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sailmon
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Joined: Sun Feb 22, 2009 6:53 pm

Re: Engine not running stalling at idle when warmed up

Post by sailmon »

Thanks for your thoughts. Still no luck. Tank vent is clear... and problem even occurred with the fuel deck fill open. Return seems ok... can see fuel running back into tank with inspection cover open. Removed and pressure tested pickup tube. No screen installed and no blockage. Engine runs well till fully warmed up (about 30 min under load) then I can hear change in pitch... runs a little rougher. It's at that point that it stalls if we throttle back to idle. If we bleed from the injector pump, we find just a little air... perhaps 4or 5 pumps on the lift pump lever. Not enough to keep the engine from running, but seemingly enough to run rough under load, and stall when throttled back. The only fuel supply item not yet replaced is the intake fitting on the lift pump... didn't have one available.

So today we install electric fuel pump in line between Racor and lift pump. Will increase fuel delivery and if the lift pump fitting is defective, might cause it to drip a bit. I'm starting to wonder if ther is a defect in the body of the injector pump that permits a small amount of air to enter. Doesn't make sense though because it should show up as fuel leak rather than air leak, being on the pressure side of the system.

Well - that's it for today's news. Stay tuned.
Bob
Sailmon (Captain Bob Allenick)
S/V Her Diamond
1991 Freedom 38
Cleveland, OH

AlanK
Posts: 127
Joined: Wed Dec 10, 2008 6:59 pm
Location: Freedom 33 Boston, MA USA

Re: Engine not running stalling at idle when warmed up

Post by AlanK »

The seals/washers on my engine at each of the fuel fittings (lift pump, injectors, bleed port etc.) are actually copper washers. Apparently they are supposed to be replaced each time although it seems they can be reused to a point. After that point when they've been compressed too many time they can leak or let air in. But since you don't have the problem when you run fuel directly from a jug it sure doesn't seem like it could be those or the lift pump or injector pump. Unless I don't remember your earlier experiments correctly.

carhelpguy31
Posts: 20
Joined: Wed May 02, 2012 8:04 pm
Location: Flint Mi

Re: Engine not running stalling at idle when warmed up

Post by carhelpguy31 »

I agree with Allan. If the concern goes away when you run a line from the liftpump inlet to a new fuel source and it goes away, I would be leary about it not being that pump as well. That test tells me the problem is either in the pickup line or in your tank. I would take a good fuel sample and check for contamination. I would also see if you can physically look into the tank for anything floating around in it blocking the fuel pick up tube.
Mike Russell
Bazinga!
Freedom 30/32
Cheboygan, MI.

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sailmon
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Joined: Sun Feb 22, 2009 6:53 pm

Re: Engine not running stalling at idle when warmed up

Post by sailmon »

Looks like the engine problem is solved. The last part we replaced was the wire mesh covered hose - right around the oil dipstick (can't remember what it is connected to - probably exits from the lift pump). Ran engine to full operating temp this evening and idled smoothly at 825 rpm when we throttled back. Again thank you for your thoughts and ideas. We leave early tomorrow morning for a 6 day Memorial Day weekend in the Lake Erie Islands. A well behaved diesel definitely contributes to peace of mind.
Fair winds,
Bob
Sailmon (Captain Bob Allenick)
S/V Her Diamond
1991 Freedom 38
Cleveland, OH

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