OK, today I've been back down to Zara to try and sort the problems out with lack of speed and the engine revving up and down on its own accord.
I have changed the exhaust manifold for a known good one (the original had 3 or 4 small pinhole perforations possibly causing seawater to enter the exhaust port?)
I have renewed the fuel lift pump for a known good one.
Taking her out, at about 1/2 throttle (appx 2000RPM) no problems, she behaved quite happily, no over revving, no soot/black smoke, all happy.
At about 2/3rds-3/4 throttle (about 2300RPM) problem manifested itself again. The engine speed would reduce by about 400-500 RPM and then after 20-30 seconds would speed up and then settle at the original 2400RPM for about 2- 3 minutes, before repeating the cycle. I didn't notice any black smoke from the exhaust at this stage.
The maximum RPM I can achieve at the moment is 2600, should be nearer to 3400 I believe?
Returning the throttle to about 1/2 way gave us a comfortable engine speed, no issues and a speed of appx 2.5 Kts. I took a sample of the exhaust water and it was fairly clear, no particles, just a very mild grey colour (caused more by aeration of the water I guess)
We then powered up to full throttle, let the engine run at that speed for a few minutes (before the engine revs dropped) and took a second exhaust water sample. This time the water was a very dirty black colour, with particles of soot contained within the sample and floating on top.
So conclusion is that we are either severly overpropped, or we have a build up on the prop or the hull.
So I took my underwater digital video camera and shot the following video:
Houston, looks like we have some fouling on the prop!!
Can you have a look at the video and give us your opinion please? The hull looks fairly clean, but judging from what I can see ( at about 23 seconds in ) we have a build up of weed and several barnacles on the prop.
Would this be a potential cause for the revving up and down of the engine on its own?
I understand that we are swinging a 14x12 prop, through a 3.26:1 ratio gearbox, a waterline length of 19 ft and a weight of apprx 4500 Lbs. Propcalc suggests a 14 x 10 prop I think, so looks like a re-pitching of the existing prop will be called for? Can we also reduce the diameter of the prop to increase the speed it rotates at, thus allowing the engine to reach its max RPM of 3400?
Any advice sought.
Thanks for any input.
Results 1 to 10 of 23
24-09-11, 18:26 #1
Continuing problems with my 1GM10 on a Westerly Pageant
24-09-11, 19:31 #2
I don't think the prop -no matter how inefficient, will cause engine to rev up and down - it will just not give push for fuel used - consistently.
If you are stuttering at high revs, you've normally got a fuel problem, however, in your case - where you mention blackness- I would suspect the air intake.
Also - don't forget the exhaust system - if a hose is collapsed it will mimmic breathing problems and give smoke and no revs/loss of power (not quite your description, but possible).
Have a think about the general age of the system, when it was last working properly etc.
Last edited by Billjratt; 24-09-11 at 19:36.Left hand down a bit.
24-09-11, 19:54 #3Registered User
Location : Scotland
- Join Date
- Aug 2001
Might be the Governor.
To be honest, it sounds like a governor problem in the fuel injection pump (not the fuel delivery pump). Basically the whole concept of a Diesel engine fuel injection system is that you set a given throttle opening to give “say” 2000 RPM and the fuel pump will try and keep the engine at 2000 RPM by delivering more or less fuel. In the case of a boat, the load is virtually constant so the only reason you would get black smoke is that the injection pump is overfuelling due to hunting.
As Billjrat has said, it may also be some other intermittent problem causing back pressure from the exhaust hose. Its not unknown for rubber exhaust hose to collapse internally causing back pressure.
One last area not to overlook is the possibility of the gearbox slipping causing the engine to race and then going under load again.
24-09-11, 20:44 #4
Cured our black smoke problem at full throttle. Don't know about changing engine speed but a clean bottom is a nice thing to have in anycase so nothing to lose. Dry her out and give her a scrub and polish the prop. Horrid job but well worth it in our case. Good luck.
24-09-11, 20:48 #5
Yes just a bit of fouling..dont think it would affect the revs
how about swopping the injector for a good one
have you checked valve clearances?
also could check all fuel pipe connections?
and fuel filters?
breather hole in fuel tank?
24-09-11, 21:31 #6
Fuel system totally rebuilt with all new hoses, tee pieces, jubilee clips, copper washers etc.
Fuel tank removed, drained, washed out, new pick up pipe fitted (made from copper, cut at angle, 30mm off bottom of tank) sealed tank flange with new gasket, no air leaks that I can detect.
Breather system OK (engine run with filler cap removed) and breather pipe is clear.
All new filters after fuel system rebuilt, thats the water seperator one and the engine primary filter.
New fuel into fuel tank after flush and clean out ( white diesel from petrol station, not red from marina)
Exhaust manifold changed, diesel lift pump changed. Temperature of engine OK, new thermostat fitted beginning of season.
Throttle linkages checked both in and out of gear, the travel on the operating crank on th eengine is the same
Last time engine ran OK was at the beginning of the season (about April) Problems started after we filled up with diesel from a local Marina.
Good idea re: the exhaust. We have short runs of hose, goint into a water trap and then into a muffler. Will remove hoses next time we visit.
Will also check the valve clearances, but can't see why that would cause the consistent speed variations?
There has been no other mechanical work done on the engine which would alter the injector/pump timing ( can this "slip" out of position accidentely?) No shims have been removed/added to the injection pump (hasn't been removed in my ownership of the boat)
I do have a spare injector and diesel pump, but reluctant to fit those (well the pump) Can the injector be swapped with a known good one without changing the precombustion chamber and copper gaskets?
24-09-11, 22:36 #7
OK Neither the condition of the prop or the bottom can vary so that is not the problem.
Fuel supply variation OR Air supply variation OR variable exhaust restriction
Fuel supply variation Could be the governor on the injector pump but unlikley. Most common cause is some kind of restriction in the supply to the injector pump. Rig up a small gravity feed tank directly to the injector pump [ use a fresh filter. ] A dinghy tank will do at a push.
Air supply variation run the engine without the air cleaner. If things are dirty run a vacuum around and spray some water to keep the dust down.
variable exhaust restriction I can't think of an easy test here. Visual inspection then substitution.
If none of the above then I suppose the injector pump governor is suspect, but as I said that is not how they fail.
Thinking outside/inside the box it could be something in the box but again they don't fail like that.
When you do track the fault down let us know please!Monkey patching programmer [retired ]
24-09-11, 22:47 #8
Will also check the valve clearances...
this is a very easy and basic thing
probably isnt but imagine the little lock nut is not tight...then the valve clearance could change
probably isnt but ....just ideas
24-09-11, 23:31 #9Registered User
- Join Date
- Nov 2007
Heavy fouling and overpropped. Each inch of pitch change will increase/decrease revs by about 250.
14*10 sounds about right. Have the prop repitched and cleaned then you will get near full revs. Don't attempt to reduce the diameter - the bigger diameter you can swing the more effective the prop - then get the revs (and speed) by adjusting the pitch. With the same engine/reduction but a bit heavier boat I had a 15*9 which is roughly the same "size" as a 14*10.
25-09-11, 01:06 #10