Intermittent Problem

[Laysula]

We relaunched yesterday after a month on the hard.On the 10 mile trip back to the Marina the engine ( Yanmar 3gm30f ) lost speed several times just for a few seconds. The engine never stopped, just slowed. Previously to the lift out it has run faultlessly and during it's time on the yard nothing in the engine or fuel system has been touched. The fuel filter and housing were changed December last year and the old diesel which came out of the old filter was clean. During the change all washers were new and the engine never missed a beat on the trip round to the yard.
I don't suspect dirty fuel,but I will drain a bit out of the bottom of the filter to check.( No glass Bowl ). So I suspect that somehow or other air must be getting into the system somewhere. I shall check all the fuel connections for tightness today but there was no visible signs of a leak anywhere.
Could there be any other reason for this malfunction? Is there anything that I have missed?
Steve

 

[dunedin]

We had that this year, and found diesel bug in the tank clogging the inlet pipe. Real pain if it is

Hope you find a simpler solution

 

[MAGTRAD]

It definitely sounds fuel related. Might be air in the system which will also be worth a check. Do the simple things first and hopefully all will be well.

 

[Laysula]

We had that this year, and found diesel bug in the tank clogging the inlet pipe. Real pain if it is

Hope you find a simpler solution

I would have expected that to stop the engine completely though?

 

[Rustyknight]

We had that this year, and found diesel bug in the tank clogging the inlet pipe. Real pain if it is

Hope you find a simpler solution

I had a similar problem some years ago, and it got worse as time went on, with the engine eventually stopping altogether. Left for a few minutes, it was possible to re-start, but it did occur when entering harbours a couple of times.

Changed the filter with no sign of crud, so eventually pulled the fuel pick up from the tank, and found it partially blocked with what looked like soggy blotting paper, which I assumed was the dreaded bug.

Luckily I only had a 5 gallon plastic tank, that was relatively easy to remove and drain before cleaning. Re-installed and filled with clean diesel, problem solved.

There probably is a rudimentary filter on the fuel pick pipe inside the tank, either gauze, or something more basic like a wire "pig tail", and depending on how much crud is in the tank, affects the symptoms...... either losing revs, or stopping.

 

[TernVI]

Crud in the fuel tank is the first thing to rule out.
If it's been two years since it was last checked, it's over due.
I would use a pela or similar to suck fuel/water/??? from the lowest point of the tank, if there is much dirt in there, you may need a bigger bore hose on the pela, the standard one will clog. A long hose with a weighted end can be poked down the filler, heel the boat to get it on the low side, see what you find.

 

[Laysula]

Crud in the fuel tank is the first thing to rule out.
If it's been two years since it was last checked, it's over due.
I would use a pela or similar to suck fuel/water/??? from the lowest point of the tank, if there is much dirt in there, you may need a bigger bore hose on the pela, the standard one will clog. A long hose with a weighted end can be poked down the filler, heel the boat to get it on the low side, see what you find.

Today I drained some fuel from the bottom of the filter and it came out sparkling clean, which I think is a good sign. I checked the tightness of the fuel lines etc and found that the bleed screw to the small Yanmar filter attached to the engine was not tight and then found that it wouldn't tighten because the thread was stripped. So next job is to helicoil the filter head and also to dip the tank probably with a length of 10 mm hose. Got to suck it up myself as the pela has been used for oil changes and I really want to see the condition of the fuel in the tank.

 

[Oily Rag]

Before you start to clean the tank, it might be worthwhile to clean the pipe from tank to prefilter. A blast of compressed air might push any plug of gunge back into the tank for removal later with your 10mm human pela.

 

[38mess]

If the engine ran perfectly after this intermittent problem, could it be something around the prop which freed itself? Plastic bag or something.

 

[Sandy]

Sounds exactly like the symptoms I had with diesel bug. Every 20 mins the revs would drop then recover. Low revs and the engine would stall but restart on the turn of the key. A jelly substance was found on the top of the filter.

Where did you get your fuel?

 

[vas]

welcome to the yanmar bleedscrew strip club...
wonder if there are any filters around without a helicoil there.
doubt it was that though, once going it's generally positively pressurised (unless lift pump is dead?) so highly unlikely to have air drawn in while engine is operating.

 

[Laysula]

If the engine ran perfectly after this intermittent problem, could it be something around the prop which freed itself? Plastic bag or something.
That was our first thought when it first happened. The Dart was full of debris but we never saw anything at the back of the boat after each episode.

Sounds exactly like the symptoms I had with diesel bug. Every 20 mins the revs would drop then recover. Low revs and the engine would stall but restart on the turn of the key. A jelly substance was found on the top of the filter.

I have drained some fuel from the filter and it came out sparkly clean with no sign of water or cloudiness. I will change the filter today though to have a look.

Where did you get your fuel?

Always bought from Brixham marina which is advertised as FAME free. Last time I topped up anywhere else was in Roscoff two and a half years ago.

welcome to the yanmar bleedscrew strip club...

Cheers

wonder if there are any filters around without a helicoil there.
doubt it was that though, once going it's generally positively pressurised (unless lift pump is dead?) so highly unlikely to have air drawn in while engine is operating.

Looking back I should have noticed that.

 

[Laysula]

Today I removed both filters and the fuel in both was sparkly clean no water and no cloudiness. The small filter has been helicoiled. So now all ready to reassemble.
Despite my efforts with 2 metres of plastic hose, it didn't seem long enough to reach the fuel in the tank through the filler.
Tomorrows job will be to empty the starboard locker of everything to gain access to the fuel tank It's a big stainless steel tank and as far as I remember from the last time I saw it there was no access hatch so not sure how I'm going to check inside. possibly through the filler tube.

 

[johnlilley]

If you have completely discounted fuel problems then one problem that can often be overlooked is a delaminating exhaust flexible pipe. this can cause similar problems in that the engine will rev when not under load but will gradually slow down when loaded as the exhaust gases cannot escape fully because of the delamination. This will often occur when the water feed to the exhaust has been restricted for any length of time and over heats the exhaust and internal delamination occurs causing blockage similar to a one-way valve.

 

[peter gibbs]

I take it you have run up the engine without load to see if it achieves and holds max revs. Still not performing?

You've secured the quality of fuel by the sounds of it - clear filters. Time to look at piping to injectors. You could turn the engine, having loosened one injector coupling in turn to blast out any obstruction. Highly unlikely to be injector malfunction.

Only small air ingress can lower power delivery. Having worked on the system recently makes me think some seal or banjo is not seated right.

PWG

 

[jwfrary]

I had a banjo back out all by itself on the positive side of the lift pump causing this kind of symtom! Bilge dry?

had white diesel in it so it caught me out looking for the source of the clear fluid! I was expecting red diesel! When the engine coughed I realised! Boat was new to me at the time!

lift pumps on these drain into the sump when they leak so worth giving the oil a smell of a diesel oudor, can be felt sometimes as well. Usually you notice your making a lot of oil when they fail badly!

 

[Laysula]

If you have completely discounted fuel problems then one problem that can often be overlooked is a delaminating exhaust flexible pipe. this can cause similar problems in that the engine will rev when not under load but will gradually slow down when loaded as the exhaust gases cannot escape fully because of the delamination. This will often occur when the water feed to the exhaust has been restricted for any length of time and over heats the exhaust and internal delamination occurs causing blockage similar to a one-way valve.

We have owned the boat for 7 years in that time she has never overheated and we have never had a problem with the water flow. Externally the exhaust looks in really good condition so whilst not discounting this I feel that it may be unlikely especially with the problem being intermittent.

I take it you have run up the engine without load to see if it achieves and holds max revs. Still not performing?

You've secured the quality of fuel by the sounds of it - clear filters. Time to look at piping to injectors. You could turn the engine, having loosened one injector coupling in turn to blast out any obstruction. Highly unlikely to be injector malfunction.

Only small air ingress can lower power delivery. Having worked on the system recently makes me think some seal or banjo is not seated right.

PWG

I think your probably right about the fuel lines not seated right, I'm changing the copper washers for some dowty ones I have ordered to make sure of a seal.

I had a banjo back out all by itself on the positive side of the lift pump causing this kind of symtom! Bilge dry?

had white diesel in it so it caught me out looking for the source of the clear fluid! I was expecting red diesel! When the engine coughed I realised! Boat was new to me at the time!

lift pumps on these drain into the sump when they leak so worth giving the oil a smell of a diesel oudor, can be felt sometimes as well. Usually you notice your making a lot of oil when they fail badly!

As Peter Gibb also said, it may be a joint that has not quite sealed properly.

 

[TernVI]

The proper test for fuel feed problems is a gravity feed from a tank of clean trusted diesel, or maybe tee-ing in a pressure gauge after the lift pump or engine filter.

Whether it's the immediate cause of today's problem or not, IMHO, it is essential to know that the lower reaches of the fuel tank do not harbour significant quantities of dirt or water, so I would check that first.

 

[Laysula]

Managed to access the tank today through the fuel gauge sender. Again the fuel was sparkly clean and there didn't seem to be any sludge on the bottom.
As said previously I think that I have to look at the security of the new connections made in the change of filter.

 

[LadyInBed]

I think that there will be a lot of people finding that they have engine and other mechanical issues having had the boat stood almost idle after what is the best part of two years.