diesel troubleshooting - low rpm

rperret · #1 08-13-2008

Having a problem all of a sudden with my 2004 yanmar 1gm10.

Prior to leaving boat idle for 3 weeks - i had the bottom cleaned and prop cleaned - and went for a sail - the motor started easily and ran strong - as it has all season long.

When I came back after 3 weeks of course the bottom seemed to look like crap - as seen from the topside. Not sure what prop looked like. I started the engine - easy start - no smoke or funny smells form the engine.

Put it in gear - seemed to be moving slow at about 1800 rpm - moved the lever to near WOT - she would only go to about 2100 rpm or so. also the engine seems to vibrate a little more than normal. Here are my thoughts on troubleshooting.

1) Prop - prior to water - i put pettit antifouling paint on - but also noticed that this stuff comes off pretty easily - perhaps when diver cleaned prop - he rubbed off all the paint and now its a barnacle ghetto..

2) fuel filter - primary was replaced spring 2007 - that said - the bowl shows nothing but diesel fuel (red) - no sign of water.

3) filter on engine - not sure when that was replaced. engine was installed in late 2004.

5) air in fuel line - so maybe bleed system? i bled system in spring - do you need to do this thruout the season??

6) air obstruction - under mid idle - i can definetly feel air intake from the filter so not sure that this is an issue.

7) exhaust obstruction - i will check the mixing elbow for buildup.

8) Bad fuel - tank was completely filled Nov 2007 - with biocide and cetane treatment. added more of both early in season when i topped off the tank. Not sure if this is an issue as the engine starts very easily.

Any other items that I missed?

Our harbor is somewhat crappy and not looking forward diving to take a look...

Rick

dmtjoy · #2 08-14-2008

Rperret,
Looks like you have it all covered and then some. I don't think it is fuel related unless it is the injector. If you have air in the fuel lines your engine will not run for long. I am thinking that if is a fouled prop. Does the engine vibrate in netueral? What is the rpm with the transmission out of gear and full throttle? ( Don't worry the governor will keep the engine from over reving.) If you have no or little vibration in netueral and you can reach 2600+ rpm then it is most likely tthe prop and or prop shaft. I saw this happen on a boat in my marina just a couple of weeks ago. Cleaned the prop and no problems.
Hope this helps.

timebandit · #3 08-14-2008

I bet it is the prop. I think some one else had this very same problem.

Rick

Omatako · #4 08-14-2008

Go for a swim

I'll bet you have a plastic bag or something wrapped around the shaft/prop.

Andre

SteveInMD · #5 08-14-2008

It could be a fouled prop or a rope around the shaft, but often these conditions will give you heavy, if not black exhaust smoke. The everything is good underwater is in good shape I would say the engine is starving of fuel (abnormal exhaust smoke is not usually a symptom here). Possible causes include clogged fuel filters, a failing lift pump, or an air leak.

Your primary filter should be a 30 micron filter, and the secondary should be the OEM filter. They should be changed at the same time.

bruceyp · #6 08-14-2008

Sounds like the experience I had. It turned out to be barnacles on the prop.
Get out the scrub brush and wet suit. Here's the thread I started a few weeks ago:
Black smoke and black water
BP

chucklesR · #7 08-14-2008

I'm betting on fuel feed constriction, i.e. replace the filters. It's not all about water in the bowl they are probably clogged. If you have a vacuum gauge you could see that.

Wraps/junk around prop would cause engine loading and smoke because a WOT is dumping more fuel than can be burned at that RPM.
Whereas WOT and still low rpm is either air or fuel constriction if no smoke of any color it's fuel. The vibration is the engine running rougher than the time wants because of misfiring caused again by lack of sufficient fuel.

Just a opinion, you get what you pay for.

rperret · #8 08-14-2008

Diver is working on boat next to mine today, so he's going to check out my prop.

Bruce - i also saw your recent post on new barnacles after 2-3 weeks - and that you have used Pettit Zinc - so did I. My LIMITED experience with the paint is that its easy to come off the surface you are cleaning. My diver claims that it helps getting barnacles off the boat - but when you scrape them off - off goes the paint. So you are back to square 1 so to speak.

My boat is in a semi-commercial harbor with a sewage treatment plant. No way I'm diving at the mooring...

Quote:

Originally Posted by bruceyp

Sounds like the experience I had. It turned out to be barnacles on the prop.
Get out the scrub brush and wet suit. Here's the thread I started a few weeks ago:
Black smoke and black water
BP

joegun · #9 08-14-2008

My shaft was turning, but the boat would not move. I thought maybe the prop had fallen off. All fine after I cleaned the prop.

robfinora · #10 08-14-2008

I would go with prop / shaft issues around barnacles. They grow faster than other times depending on the time of year and water temps.

Also- Do you have a folding prop? I do and sometimes one blade gets stuck and I need to throw it in reverse then forward a few times to free it up.

- rob