Yamar 4jh3-te won't reach max rpm and suers from blow by

Terry Cox · Sep 6, 2015

Engine RPM

We have had the same issue with our 4JH2-TE. A couple of checks:

1. What is your max RPM in neutral? Ours reaches its rated RPM of 4,300.
2. What is your RPM in reverse? Ours reaches its rated RPM of about 3,600.

When we first purchased ours the engine would reach about 3,450 in forward gear. Then, shortly after, it would never go above 2,500. I have checked everything as well. I normally cruise at 1,800, which works for me. That pushes the boat at about seven knots with our fixed three blade prop.

After consulting with several diesel mechanics, including Yanmar, the culprit appears to be the fuel injection system. Not the injectors, but the high pressure system side. To fix it means that I need to remove the system and have a shop check it out. Maybe next year. Meanwhile, cruising is more important.

If you decide to have your injector system removed and checked out, would you please let me know what you find out? I will do the same.

fstbttms · Sep 6, 2015

Prop is clean, yes? And by that I don't mean, "Yes, it was cleaned a month ago."

Ralph Johnstone · Sep 7, 2015

fstbttms said:
Prop is clean, yes? And by that I don't mean, "Yes, it was cleaned a month ago."

And the hull ............................. ?

You may also want to get a hand held tach at this point to check that your tach is reading correctly.

Ralph Johnstone · Sep 13, 2015

discovery said:
I hate to thro away a 3 thousand dollar prop if it's a engine issue, if it is a engine issue could it be the fuel pump or injector pump? How could I test it.

Looks like you're not about to get any help from either party so it's up to you to become your own engine expert.

Check this service manual to get started and invest in a hand held tach so you know exactly what RPM you're turning. The manual is only a start, common sense will probably play a much bigger part in finding a solution.

discovery said:
We had the mixing elbow inspected and cleaned, the turbo washed and the problem persisted.

I have problems with this statement. I don't think it's worth any mechanic's time to try to clean a mixing elbow. It's worth many, many hours of labour to clean one. The most likely and cheapest course of action would have been to install a NEW elbow, especially if he were a Yanmar mechanic interested in selling parts. I'd want to see the "cleaned" elbow before it was re-installed. Don't feel bad about this as it's one of the first lessons you'll learn in engine maintenance . Unless you know the mechanic and have good reason to trust him .............. DON'T.

I cannot over emphasize to start with the EASY (inexpensive) stuff first and work upwards in complexity (more expensive). This site is awash with owners who have done it in the reverse order and paid $$$$$$ the price.

Good luck and please keep us up to date on what you find.

uncledom · Sep 14, 2015

discovery said:
Help! Can't seem to properly resolve a issue we have had on our 2002 hunter 456 for the past 3 yrs. We purchased the boat in 2007 and due to ongoing fuel contamination issues tended to run the engine at low rpms, ( we eventually cleaned the tanks) then in 2012 we replaced the 3 blade fixed prop with a Flexfold 3 blade folding prop. About 6 mths to a year later we noticed some light blue smoke at startup and beyond, in addition some oil under the air intake in the engine compartment. We had the mixing elbow inspected and cleaned, the turbo washed and the problem persisted. Eventually a Yanmar tech suggested the boat was over proped and asked if I could reach the max rpm of 3700 under way, I actually had never tried, so we did, just 3200-3300 was the best we could do, at the dock in neutral it runs past 3800. Yanmar mechanic Tech says engine is over propped, so I called Flexfold, they insist its the right prop for the boat/engine, Called a prop shop, they say it specs out as the correct prop and won't touch it, So if no one will agree to modify the prop it's got to be the engine right, so I had the compression tested, it tested ok all cylinders the same just a few pds off, engine has 1900 hrs. The injectors were inspected and tested, they are ok, the turbo was inspected it's ok, but still only 3200-3300 top rpm under load. Also when I go to full throttle under load there is no black smoke ever! Also checked the fuel supply hose for blockage, also new fuel filter both on the engine and the racor 50 primary. What am I missing, also have heard from at least one other person with same boat and same folding prop and they get the max rpm. I hate to thro away a 3 thousand dollar prop if it's a engine issue, if it is a engine issue could it be the fuel pump or injector pump? How could I test it. Yanmar mechanic in Grenada points to the prop but since I have confirmed with three different sources that the prop is the correct one,I'm stumped, hopefully someone will have some ideas? The boat is a very well outfitted boat, hard dink, big stern arch, 6 jerry cans, lots of canned goods etc. but that couldn't account 5 500 lost rpm?

Had a similar problem with a Brunton Auto Prop on my 41. You are about 14% shy of full rpm. According to a tech at Mack Boring in NJ, you are lugging the engine and you are doing it through the full range of rpm. So you are lugging it by 14% as soon as you put it in gear through the whole rpm range. Think of it as having the wrong size tires on a vehicle, the gearing is off from what it was engineered to be. Just because it's stamped on the prop, do not believe it is correct. Firstly, purchase a hand held mechanical tach and check your rpms. I have one that does both physical contact on the crank pulley and can read a small piece of reflective tape via laser light. I would then reinstall my original prop and recheck. If your original prop specs out send the info of that prop along with your current prop back to Flexfold. It took two years to convince the boys at Brunton's but it's finally right. Lugging will hurt your engine, get the problem fixed, and good luck.

Ralph Johnstone · Sep 14, 2015

uncledom said:
I would then reinstall my original prop and recheck.

Definitely a step in the right direction to find out who's full of bull. Just common sense as you won't find this in the manual.

Make sure you've got that hand held tack available and then, with the Flexfold in place record:

- speed at various RPM (ensure zero current) repeat several times. Record from both tachs.

- notice of any smoke at various RPM. If you're lugging at YOUR max. RPM, there's going to be smoke.

- anything else that presents itself.

- repeat the same data collection with the original prop.

Note that this is getting towards the expensive end of diagnostics (unless you've got lots of money) with hauling and swapping props. I would still suggest taking this in progression as per my previous post.

uncledom · Sep 14, 2015

Ralph Johnstone said:
Definitely a step in the right direction to find out who's full of bull. Just common sense as you won't find this in the manual. Make sure you've got that hand held tack available and then, with the Flexfold in place record: - speed at various RPM (ensure zero current) repeat several times. Record from both tachs. - notice of any smoke at various RPM. If you're lugging at YOUR max. RPM, there's going to be smoke. - anything else that presents itself. - repeat the same data collection with the original prop. Note that this is getting towards the expensive end of diagnostics (unless you've got lots of money) with hauling and swapping props. I would still suggest taking this in progression as per my previous post.

Agree except a good diver will swap them out for about $100 per dive. So once to reinstall original and once more to install remedied flex. In theory of course.

Yamar 4jh3-te won't reach max rpm and suers from blow by

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