Diesel Guru Wanted!

[Paragon]

My problem is this, I have a small Yanmar (PMX) inboard diesel that starts great and runs just dandy, super little engine except that to keep it running like this I need to, if cruising along at cruising type revs, put full throttle on (which results in copious amounts of black smoke and a dirty stern) for about 10 seconds and then return to normal.

If I do not do this regularly, say every 5-10 minutes or less, then the engine begines to lose revs quickly (as though it had been turned off) and is only recovered (if you're quick) by slamming full throttle on! The periodic full throttle is thus a preventative measure to avoid it stopping on me.

Other than this it runs a dream and did so motoring from Fowey to Dartmouth last year, given that I kept up with the routine.

Anyone got any ideas? I have thought it may be something like an overfuelling problem but given the age of the engine it doesn't take too much before it becomes uneconomic to sort out!

All suggestions welcomed.

Many thanks

 

[dickhicks]

Sounds fuel related - have you fitted new filters? Are you using a "bug killer" like Soltron? - works well for contaminated fuel.
Is your Exhaust elbow choked with carbon?

 

[Paragon]

Not fitted any new filters or used any bug stuff at all. The boat comes out next week and I'm going to strip the whole fuel system down and clean but I was reluctant to do this in the event that this wasn't the likely cause and I would be better spending my time soucing a replacment.

What I dont understand is how it can run so sweet and reliably and just need this quick blip to sort of "clear it out". If it were carbon in exhaust, would it not be blocked all of the time? And with bugs or contaminent, would they not affect the engine all of the time?

 

[omega2]

You have an air restriction, check filter and any hoses/clips to intake manifold. Black smoke is generally created by air starvation rather than pumps and injectors suddenly altering. This advice is not gauranteed, but well worth a good look.

J HAMER

 

[seaesta]

It sounds fuel related to me. When did you last have your injector serviced?

One thing that comes to mind is the cure that the garages apply when a car diesel fails MOT because of inefficient combustion. The MOT stattions all sell diesel fuel system cleaner that seems to work very well at cleaning out fuel systems and making them run better - buy some of this and try it.

The other thing you could be doing by revving up is blasting out the exhaust system. Is there a build up of water in your exhaust line that cannot easily be vented by the engine on low revs and that is cleared when you rev up and then builds up again slowly? Back pressure in the exhaust can give very weird problems such as yours. Try running without the exhaust fitted (remember not to gas yourself or flood the boat with cooling water.

Try running without an air filter.

Martin

 

[DepSol]

sludge could get stirred up which would explain the inconsistecy.

NB Soltron allows the fuel to burn at a lower air/fuel ratio/



Dom

2003 is going to be a good year for me

 

[andy_wilson]

Some suggestions.

Back pressure in exhaust?

A de-laminated pipe could cause the faltering, but is more likely to stop completely than recover. Excess back pressure due to water traps are likely to cause an almost constant problem, not at 5-10 min intervals.

Injectors?

Most likely hard starting and constant poor running / blue smoke and evil smell.

Overfuelling?

Blue smoke again, but easy to start!! Unlikely to show intermittant symptoms.

Black Smoke?

Overloading (which under accelleration is normal) or poor air supply. Have you sound-proofed the engine box or inadvertantly blocked all the holes up. Where does the engine get it's air? Via the bilges is fine, just as long as it can breath.

I'm tempted to go with an air leak on the suction side of the lift pump. I'm not familiar with your engine at all but most have a degree of self bleeding. However an air leak like described will look after itself for a while, then cause engine to faulter (strangely, they often just cling on to life and gradually recover if you just leave it), but causing you try and 'save' it. Your intervention perhaps results in the same effect that you would expect giving it full welly from low revs?

 

[lauradee]

youve hit the nail on the head martin

prob is being caused by what you have posted, exhaust blockage caused by water not being blasted out at low revs. is the silencer sized right? by that i mean that plastic doofer that collects exhaust water.
the black smoke on full chat is because you are over propped and full revs are not obtained quickly if at all.
stu

 

[david_bagshaw]

I would suggest a small hole in the suction side of the fuel supply.

Loose joint, or rusty pickup pipe in the tank, poorly fitted filter bowl, etc

Try connnecting the engine to a portable tank nearby.

could also be a hole in the lift pump diaphram.

Air & exhaust bung ups would cause problems earlier imho.

Good luck

David
<A target="_blank" HREF=http://www.euroboating.net>http://www.euroboating.net</A>

 

[Paragon]

Thank You All

Many thanks to all of your suggestions, there seems to be a commonality of opinion as to the cause of the problem and certainly has allowed me to focus efforts in that direction.

It sounds like I should get some Soltron as well!

Many thanks once again

 

[ccscott49]

Sounds to me to be a small airleak on the suction side of your lift pump, the burst of high revs, is just enough to get the pump to overcome the airleak.
Forget the black smoke they will all do that if you ram the throttle open.
If it has a hydraulic governer, that would be the next thing I looked at.

 

[chas]

Try blowing out the return tube from the Distribution pump to the tank. If this is partially or wholly blocked, your bursts at full revs will use more fuel and relieve an over pressurised fuel system.

 

[kingfisher]

S*ltr*n for small v*lv*

Depsol,

I assumed that Soltron was only beneficial to the large gasssguzzlers you guys at Mobo use. Would my small Volvo 2001 benefit as well (mainly difficult to start, as all volvo's) ?

Is it available in Belgium

Group of people on the pontoon: skipper is the one with the toolbox.
http://sirocco31.tripod.com

 

[DepSol]

Re: S*ltr*n for small v*lv*

Benefits anyone from lawnmower users to big industrial plants.

Dunno about Belgium, will find out and send you a PM.


Dom

2003 is going to be a good year for me