HELP-Yanmar 4LHA-STP Black Smoke/Slow Acceleration

[jackryan]

Guy's

I have a few questions about my 4LHA-STP's. Decoy is a 31' Flybridge with 240 HP 4 LHA-STP's. Except for changing the impellers, I love these engines. Great fit and power for a 31' Bertram.

I've been having issues with the engines recently when I first push the power forward from idle to get the boat up on plane. The boat used to jump on on plane with minimal smoke and only take a few seconds to get on plane. Now it takes nearly a full minute to get the boat up on plane and up to full speed, and theres a huge amount of black smoke. I've had similar issues in the past when the bottom and running gear were dirty, but I just splashed her yesterday from a bottom job, and I'm still having the same issues. The engines do eventually get up to 3300-3400 RPM, but it's excruciatingly slow, and the amount of black smoke is choking people on the back deck.

The engines run up to full RPM when in idle with little smoke, but when under load, they smoke and accelerate very slowly. Once the boat eventually gets up on plane and to full RPM, they appear to run completely normally with just a small whisp of white smoke. I've changed the racors and the engine mounted fuel filters. I change the oil every 100 hours or at least once a year if I don't put 100 hours on them. The engines have around 550 hours and were new in 2004.

Some ideas I've had that may be causing the issue: I installed NON Yanmar fuel filters on the engine mounted cartridge fuel filter. They are a match in there computer, but maybe not the correct micron filter??

I've never had any work done on the injectors or valves--Could this be the problem? Thanks so much in advance for any advice/help with this.

JR

[mike ohlstein]

One engine or both?

Sounds like not enough air. Probably not those (nothing) air filters. Did you change the deck or something? Does it still happen if you open the engine hatches?

[Al C]

Not really familiar with your engines but had a similar problem with my cummins 6bta and turned out to be a turbo issue.

[Carl]

turbo issue.

[jackryan]

I'm pretty sure its both engines. I've done a turbo wash and have kept the turbo filters clean. I haven't made any deck modifications and the air flow should be the same as it always has.

JR

[SteveM]

sounds like turbos.

I had to have mine cleaned / rebuilt earlier this year. I have Yanmar 6LP's.

The boat felt like it had barnacles on the bottom and would not giddy up.

[jackryan]

Thanks for the responses. I am far from an engine expert, but the turbo's sound like they are spooling up normally. To me, it's strange that they spool up immediately and with no smoke to 3300-3400 rpm at the dock in neutral. Also, they sound and run perfectly, with little smoke at 3300-3400 rpm once she finally gets up on plane. The problem is just getting out of the hole and up on plane. At idle and full speed, everything seems fine.

[Anthony]

I had the same problem I tried several things I have had the same props on since I repowered finally I went to a smaller prop and the problem got better but was still there.I think that I only masked the problem with the smaller wheels. Finally I put on two new turbos and my problem was solved the smoke went away but now I think that I am under propped. I will put my 4 blade props back on and hopefully I am good to go I don't know if this helps or not.
Anthony

[Charlie J]

I would say turbos also

[jackryan]

Anthony,

I've stayed with the same wheels all along, so that should be a constant. I would hate to pay for new turbo's and find out that's not the problem. If my turbo's were currently bad, would the engine still operate completely normally when I run them up in neutral at the dock (I can hear the turbo's spooling up when I do this) Also, if the turbo's were bad, would I still get full rpm and completely normal operation after I get the boat on plane and up to full speed? I'm getting 3300 to 3400rpm and 32 to 33 mph at full throttle right now---that's as good as the engines performed when they were new. As I mentioned earlier, I'm not an engine expert, but it seems like the engine's performance would suffer at the top end as well if the turbo's were bad??

JR

[Al C]

Could be an air leak somewhere and your losing boost. Check your hoses and clamps around the turbo and leading to the engine.

[Dug]

Jack,

I have had mega problems with fuel in the past, and filters can cause black smoke and sluggishness.

Are you dumping black semi-burned fuel out the exhausts? If so, I am 100% with the guys on Turbo’s.

That being said, if they were doggin’ they may spin a bit at the dock. I have had two get completely stuck and the boat slugs along hard.

Dug

[Yannis]

Jack,

Please say hi to your brother!

I have exactly the same engines, same hours, same year.
I had exactly the same problem two years back. Black smoke and some hesitation.
Turned out was this honey like goo biodiesel thing.
I was extremely lucky that I didnt run the engines too much, so when I came back I had damaged only the beks so I had them removed and sent for check up, they came back ok, I might have to change one or two, minimal cost.
Other than that, as others said, its an air feed problem.
My turbo was perfect.
Good luck.

[jackryan]

Thanks for all of the feedback.

Yannnis, thats amazing that you have the same engine, year and hours! Where did you discover the biodiesel goo? Was it in the turbo's? Also, what are beks? Are they a component of the turbocharger?

Is there a way to evaluate the turbo's?

My brother and I cleaned the turbos and they seemed to be sucking a lot of air in.

Dug, There's a lot of black smoke when I push the throttles forward, but I haven't looked at the exhaust exit to see if there is black semi burned fuel coming out. I'll check that next time.

JR

[Seapalm]

Save time and money and hire a certified Yanmar mechanic... I had the same problem on one 4LH-DTE. It was the turbo and a bearing problem. All seemed well in my inspection, the mechanic found the problem within 15 minutes. You might be able to find a rebuilt turbo if that is the case. Hope it is a cheaper fix for you!

[Yannis]

Sorry Jack, by beks I meant the injectors...
I also meant that luckily I stopped before this goo went into the cylinders.
Seapalm is right, for best results ask a yanmar mechanic, good luck.

[jackryan]

I think I'll start with the injectors and filters first and see how the engines operate after that. If they are still smoking and accelerating slow, I'll move on to the turbochargers. I need to have the injectors cleaned anyway.

JR

[Rawleigh]

Just do one side until; you figure out what the problem really is.

[Carl]

If its both sides and not the Turbos I'd be looking at the fuel.

[jackryan]

I've never had the injectors cleaned, so I guess I will start with the injectors and filters and go from there. How hard would it be to remove the injectors and clean them myself? I do oil, impeller and filter changes, but this chore may be best left to the experts?

If thats not the problem, I will start with the turbo's and the fuel. Does anybody know if they sell a rebuild kit for these turbo's or would I need to buy new turbo's? The Yanmar turbo's are nearly $2000 each-OUCH!!

JR

[Yannis]

Jack,

You may be able to take the injectors out, but you certainly cannot inspect or clean or revise them yourself.
They have to be taken to the shop into a machine that does that (I cannot give many details as I’m faaar from being a mechanic).
Anyway, its not a complicated or expensive job...I’d have my mechanic do it so as to take responsibility if soth goes wrong...
On the other hand, if youre saying that youve never cleaned them, Id definitely start from that.
I would also look into my tank to see whats going on in there as well.
Good luck.

[Al C]

Jack
You can find out if your turbos are up to snuff pretty cheap with a boost gauge.

Check this link it may help you.

https://www.sbmar.com/articles/understa ... eshooting/

[jackryan]

Great Stuff, I'll leave the injectors to the experts. Also, thanks for the article on using a boost guage to test the turbo's!

[Wetline]

Jackryan
Did you find out what was causing the slow acceleration and black smoke ?
I have a single 4LHA STP with the same symptoms, runs fine at top end WOT is 3400 takes 30 to 50 sec to get up on plane with a lot of black smoke, the injectors were bench tested at 3,000 lb , the boost pressure at the intake manifold is low during acceleration with the gage nestle bouncing from 0 to 10 psi, at 3,400 rpm the boost pressure is 28 to 30 psi, the turbo fins and bearing feel tight and spin freely and look ok, I changed the fuel filters and the air filter, the fuel tank and lines look clean and are free flowing not at all cloudy. the bottom of the boat isn't dirty, I have the same prop that I had before the problem, It was a gradual not an abrupt change in the slower acceleration.
I had the air after cooler cleaned several times to insure air is flowing through it freely.

Any help would be appreciated
Steve