Engine Races Suddenly

[yachtdaemon]

Hi,
We have a Volvo MD2040 (yeah, we're sorry too) which has developed a new quirk - when charging the batteries (that is, not under load or in gear) after about an hour the engine revs suddenly shoot up of their own accord. As soon as you throttle back to neutral then re-increase the revs it is OK (for another half hour or so). It goes OK when running under load.

Initially it happened while we were at sea, and we suspected (after reading Nigel Calder) it was an over-filled oil issue, with drops being sent into the engine in a rough sea, but now it is doing it in flat calm anchorages.

We are currently in Nosy Be, Madagascar, and English-speaking mechanics are thin on the ground, so any advice would be appreciated.

Thanks,
Jill

[Freerider]

I'm far from a diesel expert, but I had an md11c which had blow by and when my surveyor was explaining possible issues from it, he talked about the possibility of a run away engine. As i understand, it can happen when blow by around the pistons can causes your engine oil to spray into the cylinders and ignite. So the engine actually burns its own oil at an unregulated crazy high speed.

The fact that you can stop it by throttling back might proof that this is not your case. There should be someone on here that knows what's going on.

[KrazySailing]

I had a Perkins 4-108 that took off racing and could not be stopped by th throttle or kill switch, had to take off the breather and block the air intake.

My problem and it is not likely yours, was diesel in the oil caused by a bad injector. It was injecting too much fuel and the unburnt fuel ran down the piston walls into the sump.
Diesel in the lubricating oil can also (on a 4-108) be caused by a hole in the mechanical diesel fuel lift pump or seals on the injector pump itself.

Any chance your throttle cable is lose or caught on something.

[KrazySailing]

I been reading other threads about reving engines and:looks like it can be cause also by:
- looks like cloged filters, etc. With the clogging you ue more throttle to get the same revs but if the line clears she reces.
- air leak, same symptoms.

[yachtdaemon]

Hi, just in case anyone else is having the same problem, we have finally got it sorted out. We had the injectors and pump "serviced" in South Africa, but that didn't fix the problem and by the time we got to Brazil, it had started racing while the engine was in gear. Waterskiing on a Westsail 32, anyone?
We were lucky enough to find an excellent mechanic who knew immediately that it was a plastic cone-shaped part in the governor that had worn and was slipping.


He also found that the "servicing" that had been done in South Africa consisted of cutting the tips off the injectors and reassembling them! That meant new injectors and a pump rebuild in a country that has 100% duty on anything marine that is imported. Ouch. Running nicely now, though.

[SkiprJohn]

Good to hear you found a good mechanic and your engine is running well. Sounds like South Africa is not the place to have your injector's serviced.
kind regards,

[Shanaly]

could be your governor aka injector pump. on our Ford Dorset this governs engine speed and keeps it constant as the load changes using a centrifuge device that looks like a mini maypole. it has its own separate oil sump - which should be serviced very 50hours like the engine. most people forget! it can get sticky /lacquered. drain it, spray in carby cleaner or you favourite oil conditioner, sluice and refill up to oil bung marker on the side. careful there are seals tiny springs and all sorts in there. a rebuild is time-consuming and skilled job, but well worth it. - its like getting a new engine . g'luck! DONT let your engine run away, they can explode.