Re: YANMAR 4JH3-HTE Diesel Engine RPMs drop and then it quits

James Alton


   Most of the vacuum gauges that I have seen used on filter installations show a yellow band starting at around - 6 psi but that is not engine specific, just general.  In my experience, with clean filters the drop should be almost nothing with the size engines we have and the correspondingly relatively  small fuel flow.  I have replaced a number of these vacuum gauges that were not functioning properly so I don’t actually have much faith in them.  I do think that you are likely on the right path and are getting very good advice here.  An air leak or a restrictive filter can certainly cause the symptoms that you are describing but there are other possibilities, a plugged fuel pick up tube, bad injection pump etc. .  If changing the filter and trying to fix the air leak does not help, consider bypassing as much of the fuel system as you can to see if that corrects the problem to narrow things down.  Running the engine from a jug and a short fuel line connected to the fuel pump can sometimes help reveal the true problem and to determine if the problem is with the engine or the fuel system.  

Best of luck to you.

SV Sueño
Maramu #220

On Jun 8, 2020, at 6:01 PM, Paul Dowd and Sharon Brown <paul.dowd@...> wrote:

Could I ask for some clarification on the use of the Racor filter gauge. My understanding is that this is a vacuum gauge and the higher the reading the more fuel blockage there is. Reading below runs counter to this interpretation. So how does one read this gauge and at what reading should I be concerned enough to swap filters?
S/Y Ya Fohi - Amel 54 #98 - Grenada
From: <> On Behalf Of Michael & Robyn
Sent: 08 June 2020 22:45
Subject: Re: [AmelYachtOwners] YANMAR 4JH3-HTE Diesel Engine RPMs drop and then it quits
Thank y'all for the suggestions and the link.
This morning I rechecked the probe I took from the engine fuel filter. It was sitting overnight in a small glass jar with a sealed lid.
In daylight I was able to spot a ~3mm diameter water bubble at the bottom of the jar.
I took probes from both Razor filters. The unused one was clean and no water. The other one had a bit of dirt and added a few more very small water bubbles to my jar.

you asked why I didn't switch to the other Razor filter.
First the filter didn't look dirty from outside shining a flash light against it. Second the pressure gauge was showing no significant low pressure. 
And in case of dirt in the fuel I wanted to keep the second filter as my last reserve for a docking under engine maneuver.

We ran the Onan Gen-set last night again for an hour.
Today I did bleed the fuel with the manual pump again. Cleaned the air intake filter, which did not really show significant dirt.

I started the engine and it would run for a few seconds without load except the alternator. I tried several times. It would start at the second attempt and run for 10 to 20s and then drop RPMs. Putting the throttle forward made the engine speed up. But it would not last and die. One could hear that it was running on one or two cylinders.
I ran the Gen again for an hour to keep batteries charged. Then a few more attempts. When the RPMs where dropping I put throttle forward.
Finally I succeeded trying to keep it at 1500 RPMs. After 10 to 15 min it sometimes speed up to 1625 ... 1650 RPMs.
After 30 min it run constant at 1650 with the initial throttle setting that gave 1500 RPMs. One could occasionally hear a missed ignition. After a total of 45 min the engine ran fine still at 1650 RPM. Since batteries where charged to 90% I reduced to idle for a few min and the engine ran smooth at 850 RPM until I shut off.
We will see how it behaves tomorrow.

I observed a small puddle of diesel fuel at the rim of the manual pump which I had hit by accident diving for probing the razor filters. 
My current assumption is that I have a small air leak in the fuel lines, maybe the manual pump itself. Or the air was introduced when the mechanic checked the razor filters.

To Giovannis point, 
I had pushed the manual prime pump to help the engine start.

Will send an update tomorrow how it went.

Thank you and kind regards

Michael & Robyn 

still anchored south of FIsherman's Island near Cape Charles entrance to Chesapeake Bay

Ya Fohi - Amel 54 #98

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