Diesel Runaway...!?

Had an unfunny experience in my car yesterday, 1.5 diesel Citroen.

Doing just over 70mph in outside lane of dual carriageway, back off throttle approaching car in front, throttle dosen`t react, just keeps revving.

At first lent on brakes but figured engine pulling against brakes would cook them and leave me hurtling with no brakes.

So put clutch in, still in outside lane at time, strain on engine as it revs out blows head gasket, think, pours oil on to hot exhaust big clouds of smoke, must have looked good to spectators, car doing just under 70 veering across road with engine reving out and smoke belching from bonnet

As it begins to slow , head for hard shoulder and switch off ignition, nothing happens, engine continues to rev...

Electric strangle valve appears to have failed as well?

Getting below 20mph on hard shoulder managed to stall thing against brakes eventually.

Fire service turned up ptretty quickly but luckily car didn`t reach ignition point.

Haven`t torn into it totally yet to find failure, but intial check dosen`t show any jammed throttle cable, wondering if its a failure with the nechanical injection pump, anyone heard of similar incident?

Also wondering why wouldn`t shut down from ignition key, one suggestion was that blown cylinder head gasket meant hot lube oil spraying into bores and acting as fuel.

The car is going to scrap as the engine is demolished and frankl;y would`nt trust the thing again, but just looking for any suggestions as to cause.

Thanks
Adam

Hello Adam,

No idea on what happened.

It's good you were able to control the situation.

It sounds like an excerpt from a movie...

Tom

I was told about possible diesel runaway problems by a friend who served in the US Navy... (note: this may be a Navy legend).

There, the problem was, for big diesel engines sometimes used in ships, when the engine began to burn oil (past rings and valve guides). Even shutting down the fuel and the air to the engine would not guarantee a shutdown. They were told to use CO2 fire extinguishers directed at the air inlet to stop the engine (hopefully).

However, a little looking with Google found this link:

[ QUOTE ]
And finally, a word about 'runaway diesels'. This is a nasty little problem which can affect any diesel where the crankcase breather pipe feeds direct into the air intake. Land Rover turbodiesels are notorious for it, and I have seen it on 1.9 Peugeot/Citroen diesels as well. What happens is that on a worn engine, gases blow past the sides of the pistons and into the crankcase. They emerge from the crankcase breather laden with oil mist from the crankcase, which feeds into the air intake. Now a diesel will run quite happily on oil mist, and so the revs will increase as this extra 'fuel' is taken in. The higher revs result in greater crankcase pressure, more oil mist is forced out of the crankcase and sucked in to the engine, and a vicious circle is created.

[/ QUOTE ]

Does this sound like your car? By the way, this could happen if A. your car engine is about worn-out (rings or intake valve guides are failing), or B. I guess this could happen if your crank case has too much oil (or the oil is foaming, or a cooling water leak into the oil).

-Bill

Very interesting. Glad you are OK.

As long is there is fuel, a diesel will continue to operate (unlike a gas engine where you can turn off the "ignition"...since there is no "ignition" on a diesel, that's not an option).

Hi Led, that happened to me with a Fiat Uno diesel years ago, exactly the same symptom, couldn't turn it off from the key, I had to put first gear and quick release the clutch pedal, stopped, and black smoke from the ex.pipe, apparently is the "deppressor" of the injection pump, keeps all time the revs that you give with the throttle, when brakes the engine jumps out running and nothing else from the pump response anymore.Fix a diesel injection pump is like a hart-operation, expensive an complicated, more in small cars.Anyway the engine of Citroen is one of the best diesels ever in Europe( same than Peugeot).
Cheers
Martin---Majorca

Actually bothered looking at the thing this aternoon.

Looks like the oil mist burner, clogged evoporater from breather pipe, and metal air intake plennum filled with oil.

Got it started,runs and revs up and just as importantly down properley, so think it unlikely fuel pump, as well as turning off wopuld drop in electric fuel stop valve, would need 2 faults to replicate symtoms. head gasket actually seems OK.

Thanks for the pointers , have talked to several mechanics about it , with years of experience, only one had ever evn heard of oil burning.

and yeah it felt like being in a movie..

Thanks
Adam

Also, if you have some sort of blower (turbo or super-charger) , oil can leak from its seals and be carried into the intake too... I thought I saw someone post that here earlier--but I don't see it now.

-Bill

Came accross some earlier Pegeot engines disliked low sulphur diesel and a seal pershed allowing diesel into the engine oil, which burnt easy from the breather system.

Have been in petrol car that dumped load of oil over exhaust manifold after being run on motorway. Blocked breather meant oil build up in air filer housing that dribbled down air intake and on to exhaust through cold start device.

Adam

Diesels can run off oil just fine. Years ago on the farm dads Massey Ferguson released its brake and took off down the hill backwards and flipped upside down. It kept running for a long time after we cut the fuel supply (dad shut off the valve and even cut the hose trying to figure out why it wouldn't stop). Tractors have an oil bath air cleaner so when it flipped the oil in the pan for the air filter started running into the intake.