Problem with my Yanmar diesel, I don't have a clue

[Mike Ebert]

I have Yanmar 6LP's, 300 HP each. The port engine became a little slow in starting a couple of months ago but no other problems. Two weeks ago when returning from a tuna fishing trip, I could not get the engine above 3000 rpm's. Both engines used to max out at 3800.

Saturday with my son and a boat load of friends, left the marina and put the throttles down. Port engine would only go to 500 rpm's. Turned around and went home.

I have had two diesel mechanics take a look at it, checked all the filters and the fuel. Neither of them could say what was wrong. I plan to have the Yanmar dealer do a full tune-up and do what it takes to fix it.

Anybody experience anything similar?

[jcollins]

Black smoke?

[DougSea]

Does the problem occur both in and out of gear? Only in gear would point to problems with your transmission or running gear.

Does she smoke? If so, what color? You could also have a fuel delivery problem, an exhaust back pleasure problem, a turbo problem... the point being, more info on the symptoms would help. Might also be a good time to join Boat Diesel (www.boatdiesel.com) and/or pick up the book by Peter Compton, "Troubleshooting Marine Diesels". I have both resources and they've been a great help. I'd look up the problem in the book for you...but it's on the boat.

Good luck!!

[Mike Ebert]

There really aren't any other symptoms. Exhaust smoke is fine, no coughing or other unusual noise, the turbo spins. I have proscan fuel meters and this engine always seemed you use more fuel (according to the readout anyway).

Once started it idles fine but when put under power it doesn't come up to the full rpm's. I think it is a fuel system problem and I'm not familiar with diesels or their injectors. It runs out of the same fuel tank as the other engine so I don't think the fuel is the problem. Fuel pump? Injectors? It did run for two weeks at 3000 rpm before it crapped out and now won't go above idle speed.

Thanks for the help.

[Merry Kate]

Mike -

The motor is not getting enough fuel. It's either a restriction in the fuel system or possibly the throttle linkage is not letting the fuel rack open. First, check the actuation of the throttle cable on the injection pump compared with the other motor (simplest thing first). Did the mehcanics 'check' or 'change' the fuel filters? If not, change both the primary and on-engine filter, bleed the system, and try putting the engine under load again. If not the filters, you need to track down the restriction elsewhere in your fuel system. All this is assuming you don't have an electronic common rail engine.

I agree with DougSea - join boatdiesel.com. Those guys will ask you a LOT of background questions to diagnose your problem, but you will learn a wealth of info about these engines. Chances are it's something simple. Good luck.

Ed

[DougSea]

Have you tried running up the RPM's out of gear (don't mean to harp on this - just not clear if this is under load or not since it points to different issues)

Do both engines really feed off of the same filter? How about the on engine "secondary" filter, was that changed? You could also just listen to each exhaust at idle; do they sound the same? Or does one of the mufflers have a different sound?

[Mike Ebert]

Thanks Doug, now that you ask, I think it did not increase in rpm's even with no load. In fact, we were playing with it in the slip so it must have not been in gear.

I didn't check the filters, I had a guy do a quick look at them and he said they were O.K. I will check them out completely and change them whether they need it or not.

Thanks again guys, I'll let you know how it turns out.

Mike Ebert

[Mariner]

Sounds like it's not getting either enough air or enough fuel. First and easiest thing to check is the filters. Replace all fuel and air filters. These should be done on a regular basis anyway, so unless you just did so, it can't really hurt.

Next is to troubleshoot the systems: fuel, air, exhaust... try to isolate the problem. Is this an electronically controlled engine? If so, there could be some safety measure that is triggering and limiting the rpm's.

[Mike Ebert]

Just to close the file, it turned out to be a loose connection of the fuel line to the Floscan guage. It was letting air into the fuel line and simply tightening it solved the problem. I thought the guy helping me was clever, he connected a small fuel tank to the engine and it worked fine, confirmed it was in the fuel line. He just traced it back.
Thanks again for everyone's help

[Mariner]

good to hear. It's amazing how little things like that can bring 300 horses of fury to a dead stop.