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Old 05-07-2020, 13:21   #1
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Yanmar Fuel

Engine is a 110 HP turbo Yanmar. Diesel tank, to Racor 500 FG filer with 10 micron cartridge, lift pump and Yanmar engine fuel filter. Last week experienced a loss of power, engine would only rev. to 2,000 rpm. Had this before and was cured by changing the Racor filter cartridge. Changed the filter and it performed fine for the next hour, then the same problem.

Now changed the engine filter and all seems well in dock but yet to take it for a run.

The odd aspect is I fitted a pressure gauge to the Racor very recently. I should have noted the normal readings, but didnt, anyway it is now showing well into the red even though the engine appears to be running well with new filters.

What else could cause elivated suction in the Racor, if the filter changes prove not to be the problem?

I can only think of a blockage in the fuel line or fuel pick up, although the fuel is good and clean. Would you blow through the fuel line?

Would a failing lift pump cause this. I assume not, and no reason to think it is failing.

Is it possible the vac gauge could be misreading. It is the tyoe that screws into the top of the Racor brass T handle that you unscrew to change the cannister. If there is air in the Racor can this cause the gauge to mis read?

All ideas gratefully received thank you.
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Old 05-07-2020, 13:30   #2
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Re: Yanmar Fuel

Very likely the dip tube in the tank is clogged, or the elbow right at the top of the tank.
Both easy to pull and check. I found mine clogged on delivery years ago by disconnecting the line from the boost pump and could not blow anything through it, stated taking things apart and my clog was in that elbow, but some boats have a sock on the end of the dip tube, God know why, cause I think it’s stupid myself. My JD Lawnmower had one and after much pulling of hair I found and removed it.
My IP did not, but she is old maybe newer ones could?

A dinghy or paddle board air pump is a good device to blow out lines, won’t easily build so much pressure to blow off lines or damage anything.

Air should not be able to cause it, and a failing lift pump would show low vacuum if anything, you have either a bad gauge, unlikely, or a restriction, much more likely.
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Old 05-07-2020, 13:31   #3
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Re: Yanmar Fuel

We had a similar problem with intermittent fuel flow, turned out to be a tiny piece of curly alloy swarf from the fuel tank (from when the factory cut the holes) that has got sucked into the line and lodged in the filter housing head right angle entry port/elbow, only discovered by luck, boat was 5 years old.
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Old 05-07-2020, 18:52   #4
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Re: Yanmar Fuel

Also make sure the tank vent isn't blocked but yeah more likely the pickup tube
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Old 06-07-2020, 00:50   #5
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Re: Yanmar Fuel

Thank you all - will report back
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Old 06-07-2020, 01:40   #6
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Re: Yanmar Fuel

I had some air getting sucked in via one of the connections to the Racor filter. But I did not know that at the time so just to get out of a tight situation I connected the hose from the tank directly to the lift pump on the engine. It solved the problem and allowed to trouble shoot in a more focused way.

So regardless of what your problem might be, it's worth just to bypass as much as you can to see if that solves the problem. If not then at least you are less likely to have a problem with the part of the system just bypassed.
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