Fuel starvation - maybe???????

[phatcat1]

Four weeks ago (last time out, we have been away since then!), we were motorsailing back from West Mersea to home on the Orwell, when the engine revs dropped from 2500 down to about 500 for a few worrying seconds, then gradually rose to normal.

This happened about 6 times back to the berth, and any movement in the throttle caused same problem!

Methinks water in seperator, gunk in filter etc, so went down to the boat last Sunday, drained and replaced filter.

Of all the diesel drained from filter and bowl, tipped into clear jug - No Water!!!!
Replaced filter - looking at old filter - looks clean, no "jelly" or excess dirt, deposits or anything obvious!

Bled system, then motored down to Harwich & back (2.5 hours running!) & no problems!

Engine seemed to be fine, but I am still worried as i found no reason!

Tank is full of fresh diesel, we always use an additive (Soltron type!) breather is fine, engine done only 260 hours (Volvo 2030)
Plastic tank (boat only 2.5 years old!) but no evidence of filter being changed since May 05.

Does the esteemed panel have any ideas or thoughts!!?!!?? /forums/images/graemlins/confused.gif

 

[ParaHandy]

as you don't mention either knocking or a highly discoloured exhaust, i'd assume the governor just decided to throttle back. Might be worth looking to see if the throttle cable attachment at either end is loose which might explain why touching it caused it to throttle back. could just be that the governor got stuck momentarily but these things are reliable ...

 

[RivalRedwing]

Sounds like it might be an air leak (any air bubbles when you bled the system?).
After leaving the engine for a day or two check all fittings in the fuel line with a white tissue to confirm integrity, also check for leaks / security of fuel filter and also injector pipes etc around the engine.

 

[pampas]

sea weed around prop ?

 

[paulwitney]

I had very similar if not exact same problem with volvo 2002.
Tried ALL the same things fuel, controls, filters etc and then discovered one night while motoring that as the revs dropped the nav lights got lots brighter!!!! Quick check with the multimeter showed that alternator was pumping out almost 16 volts - just a bit to much!! and obviously a drain on hp of the motor. The drop in revs was most obvious when the engine was cold (almost but never stalled!). I was told it "could be a problem with the earth connection to the alternator" quite possible and checked all connections. Still occurs but very infrequently and for very short periods 10-20 seconds but at least I know the cause but not the "reason" if you get my drift. PS batteries still healthy----I hope!!!

 

[Csail]

Had the same thing and it was a tiny air leak in the fuel line.

 

[Mal113]

Not all problems with diesel engines are related to the fuel supply line, a diesel engine uses fuel not only to burn in the cylinder but also as cooling for the injectors and returns it to the fuel tank. Therefore, any blockage in the return line would cause the engine rpm to drop especially when under load.

So what could be the problem: -

Suction side.

1. Fuel filter blockage… This would tend to block through dirt and in most cases remained blocked…. So I think you can forget this and you have changed the filters.
2. Air ingress…. Usually, if a large ingress occurs the engine will stop and need to be bleed to restart. A very small ingress can lower the rpm when under power and may clear when less suction is applied as the engine rpm falls. Check all hose connections and solid pipe compression joints.
3. Some foreign body in the tank that blocks or partially blocks the suction pipe.
4. The pipe mentioned in (3) goes to the bottom of the tank, any crack where it is welded to the tank case will allow air to be sucked in. Also if the crack is some way down the tube inside the tank, lets say ¾ the way down, the engine will run OK until the crack is allow to see air and then air will be taken into the system, then the boat rocks over the crack is covered and the engine picks up as normal. I have seen this a number of times. So the question you should ask yourself is what level was the full when the problem occurred? Have you filled the tank at the time the filters were changed? Is that why the problem seems to have been resolved?

Return line.

1. This can be removed at the tank and put into a bucket for testing, ensure a good stead return flow.
2. Using a bicycle or similar blow out the return line and pipe into tank.

I hope this is of held but lastly you could always provide the wife (trusting you have one) with a set of oars!!!

 

[Csail]

Must be bloody big pipes if you need a bike to check them!

 

[smeaks]

I inherrited a length of steel braided hose on the fule feed line. I experienced revs that died off and then recovered, eventually the inevitable occurred and the engine did not recover. After renewing filters etc... I found that the braided hose had degraded internally and the liner was acting as a restrictor and eventually a non return valve! Replaced all the duel lone in sight and found the engine bled in seconds rather than minutes.

 

[andy_wilson]

The symptoms suggest an air leak on the suction side of the fuel supply. These engines can self bleed but in extreme you will get this faultering effect while the bubbles are being compressed in the final run to the injector.

Start looking for air in the pre-filter (which I assume was OK when you checked before). Then check the pipes and unions between that and the engine mounted lift pump.

 

[oldharry]

[ QUOTE ]

check all fittings in the fuel line with a white tissue ..

[/ QUOTE ]

Coloured works even better, as it darkens very noticeably in the presence of any liquid, and even small traces are much easier to detect.

The original fault s almost certainly fuel starvation, and that the most likely cause is a minute air leak - if fuel is escaping, then it wil be admitting air when the pump 'sucks' at the fuel line. Also if there is muck causing temporary restrictions to the suction pipe it will slow the engine intermittently.

 

[asj1]

I had similiar symptoms 2 years ago 12 hours out from Kinsale on the way to the Scillies. The engine eventually stopped entirely, but would re-start after a short time and then die again. Eventually tracked it down to a fuel blockage in the tank end of the fuel pipe - sime crud had just blocked it inside the tank. We undid the fuel lines and blew into the fuel pipe ( well as skipper I instructed one of the crew to carry out this vital task) which cleared it. We were then in a quandary as to whether it would block again so we sailed instead and used the engine for the last 15 minutes or so coming into Falmouth - we missed out the scillies. Of course you then realise the importance of the engine for charging the batteries !

Regards

 

[billcowan]

Check also the plastic drain screw in the bottom of the fuel seperator/filter. air can get drawn in there

 

[DaveS]

Had very similar symptoms a couple of months ago and it proved to be a small air leak on the suction side of the primary filter. The presence of air at the bleed points after the engine has been left idle for some days would be good confirmatory evidence for this. Rather than try to identify the actual leaking joint, I just took all mine apart and re-made them properly - and, as a bonus, in the process discovering some plastic muck in the line which if left alone would no doubt have eventually caused it's own problems...

 

[SimonFa]

I've just had similar problems with a Volvo 2020D and came across this thread when searching for ideas. I thought I'd post my problem/solution here to help anyone else searching.

Venezia had been ashore for 4 months and the only engine running was a steady couple of knots round to my berth when she was relaunched, so don't know if the problem was do do with her being ashore.

Anyway, I replaced the fuel filters, annual service, and had a problem starting the engine. The local guru told me to just keep cranking the engine and eventually she started, with the aid of lots of lift pump pumping. Apparently the fuel pumps on these are notoriously underpowered.

Anyway, I found that in gear she wouldn't go above about 1700 revs, when accelerating she get up to about 2,200 then after a couple of seconds drop down to about 1,700. She was OK in neutral and I had tried a couple of time at high revs to see if that would clear the problem..

I've had this problem before and then the local guru came in and just blew back up the fuel line, so I tried that. It seemed to fix it but when I went out yesterday I had the same problem. I returned to my berth, had another go at blowing back up the fuel line and again she seemed ok, so I went out again - same problem.

This morning she was still showing signs of fuel starvation so I had a look at the primary filter and it was OK. So I disconnected the the fuel line at the tank and filter and gave it a good blow through, I collected the fuel but their didn't seem to be anything that could have caused a blockage.

After I'd connected the line at the tank I gave it another blow through, this time I could hear my breath bubbling in the tank, not something that I'd heard previously. Perhaps I didn't have enough puff to blow the fuel and whatever was causing the problem back in to the tank? Or when I blew the line out whatever was blocking it didn't end up in my old yoghurt container that I use for collecting fuel and filters, some fuel did miss the container so could be an explanation.

Anyway, she seems OK now.

 

[RivalRedwing]

if you believe the blockage is in the tank(?).... remember its still in there, waiting to spoil your day at the worst possible moment