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Persistant Yanmar problem.

3K views 14 replies 12 participants last post by  johnharch 
#1 ·
Hoping someone can provide me some guidance with regard to a 1990 Yanmar 3 cylinder engine on my PSC 34.

At the beginning of the season the engine experienced a sudden reduction in power. In response, I changed the fuel filter and Racor filter and bled the engine, which seemed to alleviate that symptom. A month later I experienced a sudden complete loss of power in the middle of Lake Michigan (with no wind). I could not get the engine to turn over and was towed into a Michigan harbor. The following day the engine started right up. I had the fuel examined--it is clean. The mechanic I hired in Michigan failed to diagnose any problem.

In a good stiff wind, I sailed the boat back to Chicago and was able to keep the engine going at a low RPM in order to make it into my slip. I then called Crowleys, a well known boat yard in Chicago. Crowleys replaced the fuel pump and said it fired right up. It did fire right up, followed by sudden reduction in power under load. The third mechanic I hired replaced the fuel pump that Crowleys had installed with an anti-siphon pump, which improved all symptoms.

However, problems persist. When under load, the engine is not very responsive to the throttle. I will give it some gas and the engine will act as if it is about to die, but then accelerate after several seconds. This afternoon, while in the Calumet River on my way to winter storage, the engine was completely unresponsive to the throttle and felt as if it was about to die at lower RPMs. At higher RPMs under both engine and sail, the engine hummed right along.

My next step (I think) is to replace the fuel injection pump. Any insight or suggestions would be appreciated!
 
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#3 ·
Air ingress is a good thing to look for..

Also, as ever, a question is: Has your exhaust mixing elbow been cleaned/checked for buildup or pluggage?

At one point you said the 'engine wouldn't turn over'... did you mean that literally, or did it just not fire?
 
#4 ·
To be clear if there's air in the system after its primed and bled it will be entering on the suction side. Im a firm believer in new fuel lines and double checking filters and valves for leaks, suction leaks up high on top of the Tank are especially hard to find, Iv'e heard reports of brand new shutoff valves leaking. There was a thread recently that suggested checking the return flow with the engine running just disconnect the return from the Tank and watch for a clear steady flow back to the Tank.
I had a run issue at idle and found the vent on top of the filter leaking.
 
#5 ·
How about checking your stop solenoid? Is it mechanical or electrical? Does it work loose and retard the engine rpm's? Easy to check along with the other steps suggested above.
 
#6 · (Edited)
An air leak is a possibility; but, an errant blockage in your fuel system is a much much stronger possibility.

That your system will continually restart after a resting dwell-time after a repetitive & complete shutdown is more indicative of a blockage that 'releases', loosens or rebounds after complete fuel starvation from such a blockage. An air leak would not permit the 'restart'. That your 'throttle' is seemingly unresponsive at the higher rpms would be highly suggestive of a blockage or partial blockage caused by a bacterial mass, other than the usual clogged filters - which you already changed.
The species of bacteria causing such intermittent to terminal blockages is typically Brevundamonas Aeruginosa. Colonies of B. Aeruginosa in diesel fuel looks like a mass of 'strings' and is usually confused & misidentified as 'algae'. These blockages can be found 'anywhere' in the fuel delivery system but most commonly found at/in - the tank dip tube, the tank shut off valve, elbows and hose barb fittings (!!!!) or any other 'sharp' internal surface of the tubing/hosing .... or in fuel tubing that is LOWER (in altitude) than your Racor, etc. filters.

Here's what happens with B. Aeruginosa blockages in fuel systems:
The 'strings' (colonies) are compressible and under increasing differential pressure (vacuum) across 'the strings' causes a compression of the mass which results in an even tighter mass of strings (for increasingly less and less flow), which causes an increasing reduction of flow AND increasing fuel system vacuum (further increasing the compression of mass of strings) until complete shutdown. Upon shutdown and a resting time phase allows a 'decompression' loosening of the already 'tightened down' mass of 'strings'. As the vacuum of the fuel system (after shutdown) returns to 'normal/atmospheric' pressure .... the 'strings' relax, rebound & sometimes to the extent of allowing previous 'open' flow .... until the engine's flow requirement at a later time frame exceeds the flow capacity of the mass of 'strings' (acting as a 'quasi-filter') ....... and the whole miserable scenario begins again, all over again.

So, If you are NOT regularly using a bacteriostat (BioBor, etc.) in your fuel, I would suggest the following for a 'worst case scenario':
FIRST, remove the input connection on the closest filter to the fuel tank. Use a pressure source (bicycle pump, small air compressor, etc.) and attempt to blow the fuel line clear ... back to the tank.
{DO NOT reverse pressurize Racor, etc. filters .... you'll blow out the seals and make a big oil-mess into the bilge AND break the pleats of the filter elements.}
If the fuel line is blocked or even partly blocked, THEN:
1. open the tank and carefully/gently 'suck out' some fuel from the VERY bottom of the tank near your tank's dip tube.
2. decant the fuel into a clear glass container. Hold up to strong white light and visually examine for these small 'strings'.
3. If 'strings' are visualized, disassemble and inspect the internals of the dip tube, the elbow in the tubing at the top of the dip tube and the tank valve. If nothing is visualized then totally disassemble the dip tube, including ALL connectors, and attempt to push a stiff wire 'down' the dip tube. If the wire is impeded, then remove the 'screen' on the dip tube and push a stiff wire through to clear the bacterial colony. BTW - remove and throw the dip tube 'screen' away (its of too damn small surface area to be a filter)!!!!!!!!
4. In sequence, do the same with the dip tube elbow connector, the tank valve ... all the tubing and connectors all the way to the 'first' filter in line ... until the mass of 'strings' is located and cleared.
5. FWIW - ANY portion of the fuel tubing that is lower in 'altitude' than the inlet to the first filter will operate as a 'water trap' - a great place for B. Aeruginosa to THRIVE.
6. get some vacuum gages onto your fuel filters .... zero vacuum denotes an air leak, HIGH vacuum denotes clogged filters or blockages in the fuel lines.

If you see these 'strings' .... The removal and 'sanitization' of B. Aeruginosa from a fuel system can be quite difficult. If you discover these 'strings', I would highly recommend to thoroughly disassemble ALL components of the tubing/hoses, filters, ... especially 'compression fittings' and especially any 'slip on' metal tube to hose connections **, clean them and then soak them for at least 1 hour in a 50:50 mixture of 'clorox' and water. Note** - Compression fittings and slip on hose barb connectors are notorious 'bacteria traps' which will continue to infect the system, even if a bacteriostat is used; the bacteriostat will not thoroughly penetrate such 'dead leg' connections; thus will not 'sanitize' these 'connectors'; and, the bacteria living in these 'traps' will continue ad infinitum to reinfect the entire fuel system. Once B.Aeruginosa is discovered, you MUST use a bacertiostat (BioBor, etc.) .... evermore!
Aeruginosa is an exceedingly nasty pathogen, so take 'proper precautions' when removing this stuff: gloves, safety glasses, Tyvek suit, mask, etc. etc. Dont 'mess with' aeruginosa if you have any open cuts/sores, or you have a compromised immune system, etc.

BTW/IMO - bacteria don't explosively grow in empty tanks; so, drain/empty your tank for long term (winter, etc.) lay-up; and, stop 'topping off your tank'.

If you're doing a web search for Brevundamonas Aeruginosa, it was formerly named Pseudomonas Aeruginosa.

hope this helps.
 
#7 ·
We had the same problem.....Replaced filters, fuel lines, fuel pump, replaced the fuel tank pick-up tube, and shut-off valve. Nothing seemed to correct the problem. So our mechanic...suggested by-passing the external filter (Raycor). This corrected the problem and its been running great for the past 3 years. Not saying this will work for you but it did for my boat.

Oh...he also suggested taking a a small fuel can and putting the fuel line in the can just at the fuel pump....by passing all lines and filters to see if that would make a difference under load.
 
#8 · (Edited)
Oh...he also suggested taking a a small fuel can and putting the fuel line in the can just at the fuel pump....by passing all lines and filters to see if that would make a difference under load.
Very good idea!!! as it totally isolates a plugged fuel system. A separate small gravity-feed 2 gallon 'day tank', will do the same thing.

In the same vein, Ill add another .... if you have a small 12vdc electric fuel pump between the fuel tank and the first filter in the series, the amount of extra PRESSURE that such a pump (normally used to bleed air from the system) delivers will/may overcome the initial resistance of any fuel line clogs or 'clogged' filters ... but not for long'; but/maybe, just enough to move the boat along until you reach a safe/quiet place to "sort things out, etc."
So, when the engine begins to 'stumble' due to clogging filters or the development of a restriction/blockage in the fuel tubing, etc., energizing that small 12vdc fuel pump to increase fuel system PRESSURE, while reducing engine rpm which in turn lowers the engine's fuel flow rate demand .... 'may' get you 'home' or to a port safely. No need to open up your tool kit to make the mechanical changes; just flip the switch.
Restrictions/clogs in the fuel system are subject to the very same 'physics' as the flow capacity of filters .. they are governed by the simple: "the amount of "flow rate is equal to the differential pressure across the filter/clog •times• effective surface area"; or, Q=∆P•('active' sq. ft.)
 
#10 ·
We had a problem with some similar symptoms a few years ago on our PSC 34. The engine started right up after being launched for the season. We began to motor to our slip at another marina. Everything ran well a low RPM's while we were waiting for a bridge to open, but when I increased the throttle to pass through the engine died and would not restart. We got a tow back to the marina and a mechanic looked everything over and couldn't find any problem until he found the seacock for the exhaust was partially closed. It seems we must have snagged the handle when we were retrieving a fender. Anyway it was a cheap and easy fix (for a change).
Good luck.
 
#12 ·
We had a problem with some similar symptoms ...... he found the seacock for the exhaust was partially closed. ...
... and a plugged elbow would act the same.. just sayin'... ;)
 
#13 · (Edited)
Temporarily installing a length of clear vinyl tubing in place of the fuel tubing going to the high pressure pump will let you see if there are air bubbles in the fuel going to the high pressure pump. There should be no bubbles.

Temporarily installing a compound gauge (pressure/vacuum 30inHg-0-30 psi) in the fuel line going to the high pressure pump will let you know if you have fuel feed problems. There should be a small positive pressure.

Pulling the exhaust elbow off and taking a look in the end will let you know if it is partially plugged with rust, scale, and carbon. It will be, and you can clean it our carefully with a screwdriver and hammer if it is not too bad or buy a new one if it is. Google images of 'Yanmar elbow' will let you know what it should look like on the inside. People love to saw these things in half.

And, try the engine without an air filter.
 
#14 · (Edited)
Below is an easy way to determine a Brevundamonas Aeruginosa infection in fuel oil. No 'mechanic' needed!!!

Here's the test kit: (Fuel Bacteria Test Kits), about $15+shipping; and, the 'culturing' of the dip sticks (in a warm dark place) will show results in about 1-2 days if incubated at normal (inside) ambient temperature conditions.
If the dip-sticks show higher than '10 to the fourth power' on the dip-stick indicator scale - you have quite very serious infection. If so, then the system should be sequentially dismantled and the teeny hairball of compressible and rebounding 'strings' thats causing all this grief is removed.

hope this helps.
 
#15 ·
I had a very similar problem with my 3hm35f. It would run for hours, days even, with no problem and then suddenly it would loose power, may dropping off 1000rpm. My first impulse was to change the fuel filters and that worked, for a few days. This went on and on, it would loose power and I would do something and it would work again for awhile. I ended up replacing every component in the fuel system between the tank and the injector pump. Still a problem! So I pulled the fuel tank for inspection. It had a round inspection port with a cover attached with sheet metal screws and some kind of black sealant. When the cover was put on, some of the black sealant squeezed out and dripped to the bottom of the tank. a few globs and little balls of it were free to move about in there. I cleaned it out and put better access plates on and have never had the problem since. I assume the sealant would occasionally get sucked up to the intake line and spatially block it. When I stopped and did whatever I did, they would fall off and the problem go away for awhile.
 
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