engine related

[galeus]

After quite a long passage motoring on our BMC 1.5 diesel yesterday we were pottering along and the engine suddenly speeded up with no help from us; not a massive surge, but noticable and not what it's supposed to do. All seems well at the moment and I've given it a visual check over. The fuel filter and lift pump screen were changed/cleaned a couple of months ago, but if nobody has any better ideas, I will change the filter and see... I always check the separator before any sea passage and it's always good. The fuel tank was last filled 2 years ago and I cant remember if I put any 'Grotamer fuel bug stuff in' as I have a bottle on board. We've had the boat many years and this is a first to me.

 

[pyrojames]

I have a similar occasional problem with mine, a Ford FSD, and used to have it on an old VW Polo. The polo had an air leak on the suction side of the fuel line, and I suspect the same on the Ford, but I haven't been able to find it, despite replacing nearly all of the fuel system!

 

[Boater Sam]

A short lived surge in revs is normally due to the fuel supply becoming marginal due to lack of delivery or air in the fuel lines reducing the fuel pressure to the injection pump.

Filters are always the first suspect, then air leaks. Lift pump diaphragms cause odd problems too, check that the oil is not being diluted with fuel.

Check air filters for oil mist from the breathers, if there is sufficient oil getting into the air inlet the engine could speed up to the point where it will run away and self destruct.

 

[pioneer]

When my Beta 14 surged as I was passing Felixstowe I finally decided it had been caused by passing through an area of turbulent water caused by the wake of the tug pushing one of the massive container ships into the docks. Just a thought before taking lots of bits apart.

 

[Moodysailor]

RPM's speeding up is an odd one, and warrants further investigation. It's hard to give advice as my mind is running through a maelstrom of possibilities. Everything from cavitation, transmission slip, air/fuel issue, etc.

Are you sure it wasn't a temporary drop in revs that sounded like a surge? Unless you have some sort of long-running issue, a fuel/air restriction would cause a drop, not an increase.

The only practical things that can cause an increase in revs are the load coming off the engine temporarily, or more fuel & air getting to the engine.

Sorry I can't be more specific/helpful.

 

[pyrojames]

I think getting small amounts of air in the fuel line tends to throw the governor briefly. My surges are only a 100 rpm or so for 1-2 seconds.

 

[galeus]

I've run a couple of hours since and no incidents to report.
I'll change the filter, clean the lift pump screen, check all connections and put the 'Grotamar' in and see what happens.
I will report back if any developments.
Thanks for your comments, my wife was driving at the time and says nothing got pushed or knocked to cause it.
As 'pioneer' says at this stage perhaps less is more.

 

[Biggles Wader]

Is there access to your tank for cleaning or a sump drain? Filters and Grotymar are good but there is nothing quite like knowing your tank is clear of crud to help with a good nights sleep.

 

[galeus]

It's a good point and one for next time we are doing the job's.
No, I cant access the sump but a few years ago I tied a plastic tube around a rod and lowered it to the bottom and had a good suck round. Nothing much turned up, but that was then and the boat was untouched all of last year.
We're on our summer cruise now and fingers crossed all will be well

 

[penberth3]

Sticky control rod/morse cable that moved a bit on its own?

 

[dovekie]

After quite a long passage motoring on our BMC 1.5 diesel yesterday we were pottering along and the engine suddenly speeded up with no help from us; not a massive surge, but noticable and not what it's supposed to do. All seems well at the moment and I've given it a visual check over. The fuel filter and lift pump screen were changed/cleaned a couple of months ago, but if nobody has any better ideas, I will change the filter and see... I always check the separator before any sea passage and it's always good. The fuel tank was last filled 2 years ago and I cant remember if I put any 'Grotamer fuel bug stuff in' as I have a bottle on board. We've had the boat many years and this is a first to me.

We had exactly that symptom with a Perkins 4108. Hours of motoring, and the revs increased. The diagnosis (eventually) was an air leak in the fuel line, between lift pump and injector pump - due to corrosion. First occurence was when the engine compartment was very warm. Became more frequent over time. May not be relevant. Good luck.