A mistery problem on my 2GM20F, any advice?

[abaragones]

Maybe someone here can give me advice on what to do next, the issue is:

Engine in gear doesn't pass 2800 RPM, at that point it runs rough, and black WATER ( no smoke at all) comes out of the exhaust. In neutral we hit the 3600 RPM it is rated for.

background: This same issue happened last season, after finding minor leaks in the fuel lines and lift pump (at the engine, metal hoses) and little air in the fuel we changed all components, from lift pump to secondary filter, banjo bolts, everything....issue went away...used the engine for almost 35 hours with no problem at all.

What I did this pre season: changed primary and secondary filters (O-ring etc) bleed it. Launch the boat less than 1 week ago (no fouling). After engine starting fine right after launch it died after maybe 5 minutes while in gear...lots of air left in the fuel, bleed it and started right away.

I have bled he engine in the low and high pressure areas many times, for a long period, only area I keep finding very ( and I mean very small bubbles) is when bleeding the secondary filters bleed screw. No milky fuel, just a few bubbles in the first two or three pumps of the lift pump handle, then it goes away.

AFter all this bleeding I have gain 2-300 RPM (now hitting 2800 RPM as describe above, before it was 2500 max)...but still well below normal and roughness and black water in exhaust at high RPM.

A few things:
No fouling (bottom was completely redone this season) and no changes of propeller
Shaft rotates freely
No leaks hat I can see this time
Engine hits 3600 RPM in neutral
Engine starts the first trial and doesn't die ( even after running it for an hour with load and no load)
Primary filter is a racor turbine 500
Stop cable is fully in, no issues there
Pick up tube does not have the mesh on it
Filters from last season were pristine, no algae at all and or water in the racor see thru bowl. Diesel tank looks clean.
Mixing elbow was changed last season, so almost new.
as mentioned above, all fuel lines are new from last season, including banjo bolts and washers, lift pump and secondary filter canister etc.

Any suggestion? Sucks to go through this again!

Thanks

-Abe

 

[Cayennita]

Check the exhaust hose and make sure it is not soft and collapsing. It will restrict passage and can cause the drop in RPM's. It will act different when under load. You can also check the return fuel line by removing line going to the tank and put in a short line going to a container. See how much fuel is returning. Gives you an idea on fuel flow.

 

[Stu Jackson]

Have you considered replacing that [leaky] bleed screw?

 

[abaragones]

thank you guys for your suggestions.

Cayennita, Exhaust hose is 1 season old (trident), and I have look at it and seems to be in excellent shape. What would be a good/acceptable return flow? have never been able to find that info.

Stu, no leaky bleed screws (not that I can see). I use the larger screw on top of the secondary filter to bleed and change the copper washer every(!) time I bleed it just in case.

 

[Shell]

Check for barnacles or junk on the prop.

 

[flypiscesdc]

I have the same boat and motor. Previous posts are correct in that diesels hate air and exhaust restrictions. You've said those have been addressed, so let me say this... If you have the original two blade prop on there still, you will probably only ever see 25-2800 rpm out of it under load. I had a little vibration on mine under load... Replaced the cutlass bearing... Vibration gone and now see an increase in rpm up to almost 3000 under load. Replacing prop with a three blade supposedly has helped a lot of folks see better engine performance and better boat speed under power.

 

[abaragones]

No barnacles in the prop, boat was launch 5 days ago.

flypiscesdc, I do have the original two blade prop, and although your experience could be the normal for our boats/engine, my engine easily reved up to 3400-3500 RPM in gear and run smoothly before for seasons, I run the motor for several hours last year, at 2800-2900 RPM for hours and was very smooth (after changing all the fuel lines and lift pump and secondary filter). The fact that this issue was fixed last year for 30 to 40 hours tells me that there is something wrong in the engine and it is not propeller (has not been changed) and it might be related to the filter change/Fuel system since I dint do anything else to the engine (other than oil and oil filter change and winterized the raw water at the end of last season).

Also, I think it is important that when hitting 2800-2900 RPM now (with this issue that is the max I get) it runs rough and exhaust water gets grey/black (no smoke though)

Cutlass bearing is in excellent shape.

Thanks guys, please keep throwing your ideas!

 

[Marty A]

Given that you replaced the exhaust hose and the engine ran ok last year I doubt this is the cause, but could the exhaust elbow coming off the exhaust manifold and feeding into the hose (and feeding in the cooling water) have a restriction? Some engines have a propensity for getting carbon/soot buildup and/or corrosion in this component of the exhaust.

And just to qualify, I've not had experience with this engine in particular or much experience with Yanmar issues in general so this is purely a guess.

 

[zeehag]

check your mixing elbow for clogging and corrosion.

 

[abaragones]

Thanks guys, I did change the mixing elbow and exhaust hose last year, but will disconnect the hose and check for any restrictions in the mixing elbow just to make sure.

 

[zeehag]

heat exchanger
is another problem.

 

[zeehag]

heat exchanger
is another problem. forgot f means freshwater cooled.....my ericson has a 2 qm 20 h

 

[abaragones]

Zeehag, it is fresh water cooled.

What do you mean when you say heat exchanger could be the problem? clogged?

Thank for helping!

 

[Eric M]

I hear two different issues being described.
First is the black water at high RPM's. This is nearly always caused by an overload of the engine of one form or the other. Last time we had it on our 3GM it was the exhaust elbow. Check the prop to see if you picked up a bag, or a rope, or something else since you launched since you already mentioned your bottom is new paint and you recently did new mixing elbow and exhaust hoses.
Second issue is the air in the fuel. If you are getting air in the fuel it is coming from someplace and the two areas we always seem to get air are 1 - fuel dock, the high speed pumps these days that fill hundreds of gallons in the larger motor yachts pump the fuel so fast into our tank that I have stalled out within a half mile of the fuel dock each of the last 4 or 5 times we have gotten fuel. 2 - the banjo fitting that connects the fuel line to the high pressure pump on the engine. I didn't find that leak till shining a light directly on the joint with the engine running. The spary of fuel coming out was so fine that you could not see it without the extra bright light.
Good Luck

 

[abaragones]

Thanks for your post Eric.

Will check if there is something stuck in the prop/bottom next time I am in the boat. Interesting though is that this black water issue occurred last year as well and no overload issue was found, only fuel leaks and air in the fuel.

re. air in fuel. Tank is full from end of last season, have not refueled this season. The banjo leak is something I've been looking for, although they are all new with new washers from last year. I haven't seeing any leaks but I will continue to look closer, one suspecting area is the filter canister though. I have seen a very little amount of fuel in the threats that are exposed and I have read that that area, and the (apparently too small) 0-ring can be an area of air leaks, but I am really not sure of this, could be residual diesel from bleeding.

Are there any ways to pressurize the fuel system and look for leaks?

 

[Bob16873]

I had a similar issue with the o-ring at the Racor fuel filter. Prior to leaving for a week long trip I replaced the filter. After hours of searching for leaks and priming it several times I determined that when I replaced the filter it crushed a small portion of the O-ring. At times it would run for 2 hours before losing a prime. My Racor has a bolt on the top that screws into the filter, the O-ring is on that bolt. The leak was barely noticable on the top of the filter.
Bob

 

[heritage]

You could have an air leak between the secondary fuel filter and the fuel pump. The banjo fitting have a habit of loosening while banging about on the side of the engine. I changed all the copper washers,,, they didn't leak for a few hours, but eventually would start to leak.

A better solution is to use a Dowty Washer instead of the stock copper ones. They have an 0-ring bonded into the inner edge of a standard washer. I bought mine at Laborde Diesel,. 1-800-628-9882. No more leaks.

 

[Bill Roosa]

black water is really black unburned fuel getting caught in the cooling water. So unburned fuel problem. Either it is not getting enough air (intake or exhaust restricted) or too much fuel for the rpm is being supplied (injector pump calibration), or you have a compression problem and the fuel is not igniting then burning in the exhaust manifold flames from the other cylinder(s).
Since you checked the intake and exhaust systems I'll assume that is not the problem. There is no reason to believe the injector pump has slipped calibration as you would have the problem at all speeds. that only leaves compression.
The problem only occurs at high power (read high pressure levels in the cylinders) levels so valves not seating, small leak in the cylinder head gasket, piston rings?
I'd recommend you do a compression test to see if one cylinder has a problem and see what that tells you.

 

[txtowman]

get a plastic gas(or diesel) can put fresh clean fuel in it, run a new hose from the gas can to the lift pump bypassing all lines between lift pump and tank and see if it runs.

Really sounds like it is sucking air to me. Also bypass any filter on the tank side of the lift pump.

Any leak between the lift pump and inj pump should be visible. As it will be under pressure.

May also want to check pressure between lift pump and inj pump.

 

[abaragones]

Thank you!

compression was tested last year when this same issue occurred and it was fine, and after fixing the fuel
Leaks as mentioned above, the issue went away for almost 40 hours. Maybe I should start thinking that this is a new issue not necessarily related to last year's. Will see if the mechanic can check compression again.

O rings could the source of leaks, I have double check this but will do again with color paper and bright light.

Will try bypassing the tank/Hoses/primary filter with an external tank directly connected to the lift pump and see.

Thank you again!!!