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Old 15-07-2018, 19:51   #1
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Yanmar 3ym30 won't start

Hi,

we are currently cruising The Bahamas with our Lagoon 47 equipped with two yanmar 3ym30. Unfortunately one engine stopped working and I can't get it running again. When it fist stalled I found out, that the previous owner attached the fuel supply line from the tank and the fuel return line to the tank kind of switched (supply line to the filter, return line to the feed pump. I corrected that issue, replaced the filters, bleeded the lines and the motor ran for a few days well – until it stalled again. I then discovered vey little to no diesel flow through the feed pump (even though the tank sits higher than the engine) and after opening the feed pump I found it completely clogged. I cleaned it and the flow to the injection pump is now great – but the engine will still not start. It always only fires a few times now and then.
My suspicion is, when i switched the lines the feed pump was already clogged and the injection pump sucked the diesel from the now correctly installed (but unfiltered) return line instead of from the supply line. Is that possible? I believe return line and supply line lead to the same place within the injection pump?! (The return line in my setup would in fact be able to deliver diesel constantly because it seems to be attached to the bottom of the tank. Is that acceptable or should it be connected to the top of the tank to make any backflow impossible?). I believe, as the fuel through the return line is not filtered, there is now dirt in the injection pump what is the reason that the engine won't start.
I there a way to clean the injection pump while installed? Can I carefully unscrew each of the three valve assemblies from the top of the injection pump (where the high pressure lines are attached) to see if dirt has accumulated and reassemble everything in the same order with all shims?
I would vey much appreciate any help and suggestions to get the engine running again.

All the best

Uwe Boerst
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Old 15-07-2018, 21:05   #2
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Re: Yanmar 3ym30 won't start

You could have air in the injector lines. When I help people with injector pump engines, they usually haven't properly bled the system. After the injector pump is bled you need to bleed the injector lines. Loosen the nut on the top of the injector. If you have compression release activate or remove the injectors. Crank the engine until you have clear, bubble free fuel coming out of the tubes. You'll need a towel or rags to catch the fuel.
Injectors have a check valve to keep combustion gasses and debris from entering the injector. Air compresses but liquid compresses very little. If you have very much air in the tubes, it compresses and fuel never reaches the pressure needed to overcome the check valve. No fuel or very little fuel gets into the engine. The issue can go on until the air is displaced. The fuel doesn't push out the air in the tubes unless it's a minor amount. Each time the injector is sent fuel, the air compresses, never reaching the pressure to overcome the check valve spring. Injector shown is electric, but pressure operated works the same. Pressure overcomes the spring and the needle valve lifts to allow fuel to be injected.
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Old 15-07-2018, 21:16   #3
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Re: Yanmar 3ym30 won't start

1) Re-bleed the injectors paying close attention to air bubbles and fuel volume. You may have residual air in the lines which may have moved to the injectors or a loose clamp allowing air into the system. Recheck supply pump volume, it may be clogged again. Also check flow at the injector pump, the filters may be clogged.

2) Observe exhaust while cranking ( over half throttle) over the side of the boat, you should see white smoke if the engine is getting fuel.

3) Remove the supply line from the injector pump, many have a fine mesh screen in the fitting which may be clogged.
4) If there is no air in the lines and the fuel volume is sufficient AND you see white smoke the engine is getting fuel and it should start.

5) Spray WD-40 or starting fluid into the air intake (WD-40 is safer) while cranking, if it starts and dies you have a fuel problem. You may have trash in the injectors, Remove and clean one at a time and DO NOT mix the injector parts up ( the reason for doing one at a time ) there are calibration shim washers in each one and are different pressure ratings. Any piece of dirt in an injector may cause a bad spray pattern or a stream instead of a mist. Clean thoroughly in a spotless work area, assemble and retest/ re-bleed.

Check your oil level, you may have a ruptured supply pump diaphram sucking air or leaking fuel into the crank case.
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Old 16-07-2018, 18:31   #4
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Re: Yanmar 3ym30 won't start

I found it very easy to crank it to much and fill the exhaust with raw water and flood the cylinders with water causing hydrolock. I turn off the raw water intake till the motor starts then open the truck hull valve.
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Old 16-07-2018, 18:33   #5
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Re: Yanmar 3ym30 won't start

Thru hull valve, not truck. Damn auto correct
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Old 16-07-2018, 19:26   #6
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Re: Yanmar 3ym30 won't start

Badsanta is correct, if you crank more than 20 seconds, shut the thru-hull or it will be bad!
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Old 18-07-2018, 13:11   #7
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Re: Yanmar 3ym30 won't start

I always wondered how much cranking is too much cranking if engine won’t start. I hope I never have the issue.
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Old 18-07-2018, 13:23   #8
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Re: Yanmar 3ym30 won't start

Quote:
Originally Posted by EmeraldCoastSailor View Post
I always wondered how much cranking is too much cranking if engine won’t start. I hope I never have the issue.


It depends on your engine installation. My water pump">raw water pump is slightly below waterline, so it’s pumping instantly. Someone’s pump that is above waterline could conceivably need idle RPM to prime. I have a large muffler well below the engine, someone else may not.

If it doesn’t start right away and you are going to start trouble shooting, step 1 really ought to be close the seacock.
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Old 19-07-2018, 06:08   #9
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Re: Yanmar 3ym30 won't start

Thank you all of you for your quick support. We finally got the engine running again - after carefully bleeding and through a separate jug with diesel. When I checked the diesel flow it was always good but there seems to be some dirt moving back and forth in the fuel line between the tank and the first filter that occasionally clogs the line. At least we narrowed the problems...
I never understand, why the fuel line to the fist filter is not that wide, that all dirt that accumulates in the tank over time can easily move to the primary filter. Instead it clogs the small drain pipe at the tank at a location where it is very difficult to reach!
Anyway, thanks again.
Uwe
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Old 22-07-2018, 21:02   #10
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Re: Yanmar 3ym30 won't start

Several times I have seen algae growing in diesel tanks. It's brown and the consistency of jello. It will frequently plug pick up tubes and screens and is not easily seen in the tank. It moves and causes intermittent stalling and no start conditions . Draining the tank and inspection with a good light may reveal the culprit. Remove the slug of goo and treat with a biocide.
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