Yanmar 4Jh4-HTE Manual fuel priming lift pump

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Im looking for someone who has or knows for sure, or better still can check, whether the manual priming lift pump plunger (ie the part you push down to prime) on the 4JH4-HTE engine is sucked down on a running engine or it remains up and you can still prime or pump it.

Background:
The Hunter 49 fuel line out of the factory went from tank to Racor filter to the Yanmar fuel filter shown in the attachment, which has a manual priming button on top, to the injector pump and back to the fuel tank. ie no electric or mechanical external fuel pump. I believe however there is a small (low pressure) pump integral to the actual injector pump, but not something you can replace separately.

I got a dose of bad fuel some months back replacing filters, cleaning tanks, replacing the fuel etc However no matter what I did I could not get it back to a state where it would run at much more than 1600 rpm for more than about 3-5 min. It effectively had the symptoms of being starved for fuel. In the end to get going and have some reliability I added a very expensive electric Yanmar lift pump. As a result it ran perfectly, as it had done before the bad dose of fuel and having to add the lift pump.

At the time I decided either the manual priming pump or the fuel pump inside the injector pump itself had to be the issue, as this was all that I figured was left. I theorized that the manual priming pump must have had a pin hole in the diaphram, or we had damaged it from a lot of use. Before I added the electric lift pump, we had been pumping it a lot to keep the engine going many times, and then I noticed that sometimes while running it would suck the plunger down other times it would not.

So I have now finally received a new priming pump/filter/sensor installed it and removed the added lift pump, so back to original.
So far in neutral it all runs up fine. But the primer pump was still sucked down, not hard like on the old one, but none the less, still probably 3/4 down when the engine is at idle. I need to know if this is normal or not ?

Test run tomorrow to see how it goes under load above 1600rpm.

 

[jssailem]

I have a Perkins not a Yanmar diesel.
I have observed the same issue, you describe, happen on my manual/engine driven fuel pump. It is the fuel feed pump drawing fuel from the tank through the Racor filter, pushing it to the high pressure injector pump.

I note that the Yanmar Manual shows an electric Fuel Feeder Pump.

Your addition of this will assure that fuel will get to your engien as you increase the demand RPM's.

 

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Yea this particular model Yanmar engine is not supposed to need and external pump of any sort and that is where Im trying to get back to. It never had any external or separate mechanical pump for the prior 15 years from new. From what I read the injector pump assembly on this engine is not like normal injector pumps and inside the injector pump assembly is a small conventional type pump section along with the high-pressure injector pump. All in the same assembly, hence why there is nothing else.
So another Hunter owner with the same configuration as mine has responded to my post in the Facebook yanmar forum saying his mechanical primer pump knob stays up. So I'm guessing there may still be some restriction and perhaps this is why its sucking the pump bob 3/4 of the way down. Just a theory at this point.

 

[jssailem]

Sucking it down implies a vacuum is being created. Since you say the high pressure pump has a low pressure pump. It is where the vacuum starts. Since the manual pump is affected the clog is likely between the manual pump and the fuel tank. If nothing is found in the lines, then take a look at the pickup tube. Perhaps there is a screen at the bottom of the tube and it has some junk clogging it.

 

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So today, I ran from a jerry with new hose to yanma filter on the engine and feed the existing return line back to the Jerry can . Thus isolating the existing feed hose, Racor filter, intank pickup hose and the tank itself. Everything ran as it should and the primer pump knob stayed up. So, either the problem is in what I have bypassed, or the fuel pump(inside the injector pump) is somehow weaker and now the extra load of the Racor prefilter is enough to tip the scales.

 

[dlochner]

Have you inspected the fuel pick up line inside the tank? Sometimes there is a screen at the end of the line which gets clogged and restricts flow. If it is clogged, remove it, it isn't needed.

Next up would be replacing the hoses. If you had bad fuel it may have clogged the fuel line. Initially the clog may have been small, but over time as more crud got sucked up, it became more clogged.

Check all the fuel lines for cracking or hardening. If there is a small air leak into the line it will break the prime and there will be insufficient fuel flow.

Replacing the fuel lines will be a lot cheaper than replacing an injector pump.

 

[jssailem]

Thus isolating the existing feed hose, Racor filter, intank pickup hose and the tank itself.

Yes. Great way to isolate the problem. I think simple at this point. I would look for fouling/clogging in the isolated section of the system.

• existing feed hose, (Open each end, blow out clean, re-connect)
• Racor filter, (Empty, clean, checking the intake and exit connections for fouling.)
• intank pickup hose (Remove from tank clean replace)
• and the tank. (This one is tricky. If you have much fuel, I would look to trying treatment of the fuel with chemicals that will dissolve/kill the biologicals that foul fuel. I used this method to rid my 85gl tank of goo. I used the Racor to help capture the dead crap. $10US for filters was way better than $2500 for a tank polishing of all the fuel.)

Here is what one of the filters looked like as I processed through the old fuel. I got good at changing the Racor. It only took about 6 filters to get clean fuel. Now I change filters (when my engine is running about every 8-10 months depending on engine usage. I added a vacuum gauge to the line just after the Racor to help me know when the filter is getting clogged.

 

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Firstly thankyou to all those that contributed. You did lead to me finding the problem.
Effectively this problem (fuel starvation) started nearly 12months ago and you may have read my earlier posts
It stemmed from 700L of bad fuel and was complicated by a lack of filters.
Eventually back then I got it going reliably by introducing an expensive electric Yanmar lift pump.

The problem I have been chasing recently embarrassingly turned out to be self-inflicted at some point.
Over the last few days in fear of the problem being in the Bosch VE injector pump (ie many dollars) I started again.
The first thing I did was to get a new Jerry can , new fuel, new hose and ran intake and return fuel lines directly to the engine, and that worked just perfectly

From then on it was a slow process of elimination, till I found the problem.

Where the Racors are installed I look down on them, not horizontally which is my only pathetic excuse.
On the top is a white knurled fitting on a plunger used to prime the filter assembly.
So you loosen it, pump a dozen times and it fills the filter with diesel. Nice idea.
However if you don’t screw it all the way back down, as shown on the right (see image) the plunger blocks nearly all of the input/suction.
Either on the last filter change or perhaps the one before, I must have done this and the electrical Yanmar lift pump I added was enough to pull the fuel past it.

Now all is well, the Yanmar primer pump knob stays up as you guys told me.

Thankyou

 

[kappykaplan]

The problem I have been chasing recently embarrassingly turned out to be self-inflicted at some point.

"We have met the enemy and he is us" immediately comes to mind. Great detective work to resolve this.

 

[dlochner]

Self-inflicted wounds are painful. I'm sure most of us have experienced them. I couldn't figure out why my brand new alternator wasn't putting out any current. Double checked the regulator programming, the wiring, took it to a local auto electric shop, and sent it back to Balmar who said the alternator was fine. Turns out, when I installed it the first time I had turned the alternator disconnect switch off and forget to turn it back on.

 

[shemandr]

I'll confess that instead of bass fishing one fine morning I was trying to start the outboard. Two trips to NAPA, hair pulled out and eventually noted a switch on the control consul. "What's this?" It was a kill switch which had been inadvertently moved to the off position.