Yanmar 4JHTE loss of rpm,s

[magique]

We have been having a problem with our yanmar 4jhte for a couple of years down here in the Caribbean. It will sit an here an purr like a kitten while charging the batteries. On a passage it will run very smoothly for a couple of hours and then it will slowly lose RPm,s and finally stall . It will start again immediately but continue to lose rpm,s . Shut it off for an hour or two and it,s good again for an hour or two. We have changed filters , blew out lines ,bled the lines , polished the fuel , turbo washed the turbo charger. Still acts up , we are going to have inspection ports installed on our fuel tank ,and hand wash the tank. Any ideas on what the problem maybe , what is the best solvent for cleaning the diesel tank ?

[Vasco]

Do a search I think the turbo problems have been discussed here before.

[Navicula]

if you have a racor filter.....you may want to check for blockage in the housing.......do you have a vacuum gauge on the fuel filter...

[CAELESTIS]

Check your fuel vent line. Sounds like it is partly clogged.

[Safari38LH]

Had the same type problems a few times. First time there was stuff in the fuel tank big enough to block the intake. After the engine shut down it would float away due to lack of suction. Years later the problem returned but it turned out to be the Racor leaking air. We found it by bypassing the Racor and finding that the engine then worked well. Had to replace the Racor to fix it.

[DeepFrz]

+1 on the fuel tank vent. It sounds like you are getting a partial vacuum in the fuel system.

[TacomaSailor]

The clogged fuel vent sounds likely and would be the first thing I'd inspect. But, my 4JH2E (non-turbo) did the same thing for months in late 2012 and it was not the vent. At that time I'd had the boat 18 years and had never had a single diesel fuel feed problem.

I tried all the stuff you tried and I also inspected the fuel tank several times and saw no problem. The tank has an 8" inspection plate and I can reach in to touch the bottom of the tank. I could clearly see the pickup about an 1" off the bottom with no debris or anything else visible.

After several episodes of what you describe I decided to do a serious tank inspection. There were about 5 gallons of diesel remaining in the 55 gallon tank when I got serious about the inspection.

I reached to the bottom and scooped out a bunch of clear gelatinous material - it was the consistency of not quite set jello and was absolutely clear. I could barely see it in my hand.

Even knowing the stuff was in the bottom of the tank - I could not see it when shining a light into the tank.

I spent hours cleaning the bottom of the tank and eventually removed several quarts, maybe even a gallon, of the stuff from the bottom of the tank.

After that -no more problems with the Yanmar.

[Snore]

Originally Posted by CAELESTIS

Check your fuel vent line. Sounds like it is partly clogged.

assuming no visible fuel leaks- including when engine is off then +1 for check the vent.

Easiest way to check the vent is to either open the fuel fill (dangerous at sea) or pull vent hose and slap a temporary one on (less dangerous, but still risky). Alternative is to run the engine for a few hours at the dock, get it to stall and start working the options.

[magique]

Thank you for all the replies and good advice. Am having the tank pumped out today and installing inspection ports ,will give the tank a good cleaning and let you know if it works.

[ontherocks83]

Originally Posted by TacomaSailor

The clogged fuel vent sounds likely and would be the first thing I'd inspect. But, my 4JH2E (non-turbo) did the same thing for months in late 2012 and it was not the vent. At that time I'd had the boat 18 years and had never had a single diesel fuel feed problem.

I tried all the stuff you tried and I also inspected the fuel tank several times and saw no problem. The tank has an 8" inspection plate and I can reach in to touch the bottom of the tank. I could clearly see the pickup about an 1" off the bottom with no debris or anything else visible.

After several episodes of what you describe I decided to do a serious tank inspection. There were about 5 gallons of diesel remaining in the 55 gallon tank when I got serious about the inspection.

I reached to the bottom and scooped out a bunch of clear gelatinous material - it was the consistency of not quite set jello and was absolutely clear. I could barely see it in my hand.

Even knowing the stuff was in the bottom of the tank - I could not see it when shining a light into the tank.

I spent hours cleaning the bottom of the tank and eventually removed several quarts, maybe even a gallon, of the stuff from the bottom of the tank.

After that -no more problems with the Yanmar.

Did you ever find out what the clear stuff was and more importantly how to prevent it?

[HappyMdRSailor]

You've got all the info you need here.... These guys know their stuff....
1. Tank Jello
1a. fuel supply restriction
2. Tank vent
3. Air leak in supply line
Nuff said...

[Dale Hedtke]

It sounds like you have the problem well in hand. For what it's worth, here is a similar problem we encountered: the fuel pickup line into the tank had a screen on its end. Junk from the tank would collect on the screen under suction, shutting down the engine. The suction would end and the junk would drop off. I did see a high vacuum reading on the Racor's gauge.
In hind sight, why would you want a screen on the suction line? I think that you would want to suck any gunk out of the tank and catch it in the filter on an on-going basis.

[hpeer]

Originally Posted by Dale Hedtke

It sounds like you have the problem well in hand. For what it's worth, here is a similar problem we encountered: the fuel pickup line into the tank had a screen on its end. Junk from the tank would collect on the screen under suction, shutting down the engine. The suction would end and the junk would drop off. I did see a high vacuum reading on the Racor's gauge.
In hind sight, why would you want a screen on the suction line? I think that you would want to suck any gunk out of the tank and catch it in the filter on an on-going basis.

I had a similar issue, I cut it off. Calder addresses this in one of his books, came to same conclusion as you.

Had a weird one last summer. I could not remove my fuel fill cap, ended up breaking it up to remove. Had been sitting for two years.

Anyway, got bits of the plastic cap in tank, big enough to partially jam fuel pickup. I ran a bit of SS rigging wire down the fuel hose from the fuel filter long enough to run the end of the pick up. That kept the crud out. Obviously a temp solution.

[magique]

Well the problem has been solved ,I had hired a fellow to come and pump out the fuel today and to install inspection covers . He came pumped out the tank ,opened the small cover that the sender is on ,said the tank and the fuel we're clean. He checked the fuel pickup line and it was plugged full of dirt. Also the end of the pickup line in the tank was laying on the bottom ,so he shortened it to just clear the bottom of the tank. He said not to bother with the inspection ports.
Thank you everybody for your input .

[HappyMdRSailor]

Originally Posted by magique

Well the problem has been solved ,I had hired a fellow to come and pump out the fuel today and to install inspection covers . He came pumped out the tank ,opened the small cover that the sender is on ,said the tank and the fuel we're clean. He checked the fuel pickup line and it was plugged full of dirt. Also the end of the pickup line in the tank was laying on the bottom ,so he shortened it to just clear the bottom of the tank. He said not to bother with the inspection ports.
Thank you everybody for your input .

Thanks for the resolution post magique!!!

Glad it was as simple as that!