4LHA-STP Oscillating idle

[Ed Malone]

Hello All,
Feels strange to post this problem on a Cummins site, I hope no one gets offended, but I could use some help with my Yanmars!
Anyone have any experience with the governors on the 4LHA-STP? Engines have 600 hrs on them, burn rates are the same and incredible, oil samples are flawless, my only problem is my port engine seems to fluctuate rpm at idle no load. I’m set to 750 rpm, and it wants to float between 750 and 800 on about a 3 second interval. This only happens under no load, as soon as you engage the gear it’s steady as can be. I should also mention, if you crack the throttle a little bit and allow it to return to idle, it seems to stay steady for 30 seconds or so. All filters have been done at least three times, there is definitely no air in the supply. Any Thoughts?
Thanks for taking the time to take a look and for any input you may have.

Thanks, Ed

Topic

[Ed Malone]

Very observant!

Yes the docks were replaced after Sandy………… pretty much EVERYTHING floated away to some extent. That’s why I went to Massachusetts to find my boat. Lol. I can’t say enough good things about Nichols Marina. It’s gorgeous.
As far as attempting any adjustments, it truly hasn’t acted up enough for me to try anything as of yet…….. I’ve decided to take care of Installing New thermostats and a coolant change, so of course next dilemma…….. I’ve been trying to source the Delo ELC that it seems replaced the Texaco product Yanmar asks for for a solid week. It’ll be here tomorrow……….. except each tomorrow is the same response. Lol.
I’m thinking of going with Rotella Extended Life Coolant Nitrite Free…….. anybody know if this is advisable?
Thanks as always, Ed.

[Rob Schepis]

Ed,

Really nice comeback post, well said and much appreciated!

Are you photo-taching the engines or do you have Aetna tachs?

BTW, the docks in your pic look really nice, all new after Sandy? I know your area got hit HARD by her..

[Ed Malone]

Thanks so much Tony

I appreciate the picture, as I also saw the post about the 6ly’s…….. I would have gone for the cap below the one you indicated, which is why I left it alone until I got a reputable reply! I can not say enough good things about this forum, it says a lot about a man who will give legitimate helpful and honest advice to fellow boaters without feeling his business is threatened………. I appreciate you guys beyond words…….. Any parts I have to order will definitely come from SBMar. I will see how it goes with this adjustment over the weekend, I’ll keep you posted.
I’ve owned this particular boat three years now, and also noticed that when you dump her in gear at idle, you get a frump frump frump frump frump frump, then a decent idle. Mentioned that to my experienced engineer at survey, he said “they’re Yanmars, that’s what they do”. Any opinion? Tony, if you find yourself in NY, I’ll make it worth your while to spend some time with me! Lmao.
I’m sorry, I just don’t trust people that haven’t earned it with my baby’s engines. I know there are certified mechanics around, I’ve just seen too many parts get changed without a result. Thank god for you guys and this forum.
Ed.

[Tony Athens]

Yanmar 4LHA Idle Hunting Issues

Ed,

Glad you joined up.. We are here to help and a few us of know your engine really well.

I went back and snooped around at bit as I remembered something similar to this on the big brother of that engine (6LYA), and found a tech bulletin referencing idle hunting. Attached to the post

Also attached a pic of the bumper spring location on your injection pump. You might consider removing the cap, loosening the lock nut and rotating screw CW a 1/4 to 1/2 turn.. Your can always go back and try the other way too.. Nothing scary and it may also require resetting of the idle screw itself.

Another possible fix may be the tolerances in that pump may some extra “lube in the fuel”. 1 quart of ATF per 100 gallons of #2 may help–Pre-mix in a gallon first before you dump it in the tank

BTW, a really great engine!..

Tony

[Author]

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