Yanmar Diagnostics

[Ip485]

Would appreciate some thoughts on simple diagnostics.


Engine is a 4JH3-HTE - so a turbo charged Yanmar. Occasionally I have had a loss of rpm so the engine will only rev. to 2,500 instead of 3,500 under load. Almost certainly it will prove to be the filters need changing - in the past that has solved the problem on a couple of occasions.


However, there are a few other things that I think can cause this;


1. Failed or slow turbo charger,
2. Failed or failing electric fuel pump,
3. Blocked or partially blocked injectors,
4. Blocked fuel lines.


I would be interested for each any pointers on simple diagnostics to determine if the components are working?


I would also be interested to know how often people find they need to change fuel filters.



I have a Racor as the primary but I do use a 10 (I think need to check) micron filter which is the smallest size.

[LeaseOnLife]

Originally Posted by Ip485

1. Failed or slow turbo charger,

I can't think of an intermittent failure mode on a turbo.

2. Failed or failing electric fuel pump,

do you have an electric pump additional to the mechanical lift pump? if so... maybe.

3. Blocked or partially blocked injectors,

I don't think so, typically old injectors will not spray as nicely and cause black smoke, but nothing that sometimes work and sometimes not.

4. Blocked fuel lines.

very possible, including junk blocking the intake of the tank, falling back when engine is off.


Racor offers a vacuum gauge to tell you when to change filters. It also would indicate a blockage on the suction side. I only change my Racor filter when the needle creeps beyond the middle of the yellow range.

[a64pilot]

2 micron is the smallest Racor I know of, although most of us run a 30 because the filter on the engine is the fine one.

However most probably your sagging RPM result of fuel delivery, filter, clogged fuel tank vent, collapsed fuel line, blocked fuel line, there are many possibilities, but they all result in the engine not getting the fuel it needs.

A Racor vacuum gauge on your filter is great for troubleshooting, it can confirm blocked fuel passage, you need to start checking and cleaning until vacuum is gone.

[bstreep]

We have a 4JH. 1990 model, with turbo.



The turbo CAN get slow. It will carbon up, if not regularly run hard. Eventually it will stop completely. Turbo wash, that Yanmar sells, is supposed to be used - get this - WEEKLY. I swear it is Fantastic spray cleaner. Smells exactly like it. Anyway, we just recently had our turbo rebuilt. I can pull it and replace it in about an hour and a half each way. They need to be run hard, and run hard often, which is difficult to do on a sailboat. The turbo uses crankcase oil for lubrication and some cooling, and changing it often is critical. Keeping the carbon levels down is also critical. Good luck.

[a64pilot]

You only wash the suck side though and that only gets oily from blow by no carbon there. Carbon is the turbine side from exhaust

[bil56]

Originally Posted by bstreep

We have a 4JH. 1990 model, with turbo.



The turbo CAN get slow. It will carbon up, if not regularly run hard. Eventually it will stop completely. Turbo wash, that Yanmar sells, is supposed to be used - get this - WEEKLY. I swear it is Fantastic spray cleaner. Smells exactly like it. Anyway, we just recently had our turbo rebuilt. I can pull it and replace it in about an hour and a half each way. They need to be run hard, and run hard often, which is difficult to do on a sailboat. The turbo uses crankcase oil for lubrication and some cooling, and changing it often is critical. Keeping the carbon levels down is also critical. Good luck.

ouce:

[Ip485]

Thank you everyone - well as so often the case you proved exactly right - the filter required replacing. While at it I also disassembled the Racor and gave it a good clean. Turned into a total PITA as the fuel pipes screw on and the threads are impossiblly difficult to get on - or were on one!



I also took the opportunity to fit a Racor pressure gauge to the top of the Racor, which was easy to do and appears to work very well. (as suggested here).



My starting pressure was mid way between 0 and the start of the orange band - which I assume is normal.


I am assuming the gauge is simply measuring the vac in the Racor and that if for example the engine filter required changing there would be no difference in the reading? I didnt change the engine filter as this had been done relatively recently but wondered with both changed if the reading would be any different. I have convinced myself intuitively it would not.


Thank you everyone.

[Dockhead]

Originally Posted by Ip485

Thank you everyone - well as so often the case you proved exactly right - the filter required replacing. While at it I also disassembled the Racor and gave it a good clean. Turned into a total PITA as the fuel pipes screw on and the threads are impossiblly difficult to get on - or were on one!



I also took the opportunity to fit a Racor pressure gauge to the top of the Racor, which was easy to do and appears to work very well. (as suggested here).



My starting pressure was mid way between 0 and the start of the orange band - which I assume is normal.


I am assuming the gauge is simply measuring the vac in the Racor and that if for example the engine filter required changing there would be no difference in the reading? I didnt change the engine filter as this had been done relatively recently but wondered with both changed if the reading would be any different. I have convinced myself intuitively it would not.


Thank you everyone.

This should be a sticky.


There are a number of 4JH3 owners, including me, who have had EXACTLY the same problem, with EXACTLY the same cause.


I don't know whether this engine is particularly sensitive to resistance in the fuel system or not. But my case was a slight blockage in the fine filter which CANNOT be detected by the vacuum gauge on the Racors.


I had been stretching the fine filter change interval because I was using 2 micron elements in the Racors and they were staying clean. Logically, nothing can get through those to the fine filter, but it turns out that that is not so. Now I change the fine filter religiously and I have had no further problems.

[LeaseOnLife]

Originally Posted by Ip485

I am assuming the gauge is simply measuring the vac in the Racor and that if for example the engine filter required changing there would be no difference in the reading? I didnt change the engine filter as this had been done relatively recently but wondered with both changed if the reading would be any different. I have convinced myself intuitively it would not.

Yes, a plugged filter on the engine would not show a different reading on the racor gauge.



With a new filter in the Racor, and the needle going close to orange, you might have additional restriction(s) between tank and Racor, which does show on the gauge. On my Yanmar 4JH2TE, I barely get to yellow at high load, with a new filter. Or maybe your engine sits quite a bit higher than the tanks?

[Ip485]

Leaseonlife - interesting post. I will check my gauge at various power settings now all is running well next time and see what the range is.


Dockhead - thank you, it does seem a common issue, especially at the top end of the power range.

[NYSail]

Try removing the fuel line from tank to racor...... remove at racor side and blow into it. Possible
A
Restriction in the tank pick-up. First time I did this with Old engine I felt a pop.... must have been crudding up, however had no signs with engine performance.

Good luck
Greg

[a64pilot]

Originally Posted by LeaseOnLife

Yes, a plugged filter on the engine would not show a different reading on the racor gauge.

Yes, it should not. It can’t, it’s upstream of the gauge.
And yet mine did. I still have not figured out how though, but it did. I had a high restriction, changed to the other filter, it went down a little but not much, engine started slowing down, I switched to both filters, didn’t make much difference, changed both filters, still high restriction.
Took fuel dip tube out verified no restriction from it to the filters.
Still high vacuum, changed engine fuel filter out of desperation, vacuum dropped immediately.
I can’t explain it, I don’t even understand how, but my clogged engine filter did cause a high vacuum gauge reading on my twin Racor primary set up.

[bil56]

do you use an anti-bacterial treatment?
it would be good to consider a complete fuel tank cleaning ...