Red lining a diesel

Adstar · Unread post by **Adstar** » 17 Jul 2006, 15:25

I don't know how, I am assuming something caught either the throttle cable or my feet, but I managed to red line my previously well respected 2.1td (in my 96 605). It decided to shut itself down, and eventually let me restart it! With clouds of what I assume was unburnt diesel covering the road!

After 300 miles I think I have got away with it! It still pulls.. and it still runs.. no oil or coolant loss.

But I have not owned a diesel long enough to know what damage I could have done!

Although I have decided to rush the saving for the cam belt replacement!

rossd · Unread post by **rossd** » 17 Jul 2006, 16:27

How many miles has the car done, does it use much oil between services? The only reason I asked is because this could have been a "runaway" where the engine runs on its own oil, due to bad rings, or leaking turbo bearings. I wouldnt have thought a stuck pedal would have produced that amount of revs, unless you had previously had your foot to the floor when it did it.

What were the exact circumstances?

AndersDK · Unread post by **AndersDK** » 17 Jul 2006, 17:17

The diesel rotary pump itself does the rev limiting. No matter if you push the pedal out the floor. If this setting is mengled with - you risc the engine is running into a sudden death - when the MOT'ter is doing the smoke test

The differences in working principles for petrol and diesel engines makes for optimum Bhp at high revs for a petrol - and about the opposite for a diesel.
I.e. a diesel will have such high internal losses at high revs - that it hardly produce any usable pull. Besides it will rather quickly die for good if not shutted down shortly.
Above some 4K revs there are no significant pull from a diesel. Its completely useless to try rev a diesel higher for more power.

Adstar · Unread post by **Adstar** » 18 Jul 2006, 08:34

The exact circumstances...

I had just been pottering around town calming down after having soundly thrashed a little wicky boy in his poor little metro (got caught up in a cruise leaving the KFC. Some VERY nice machinery and also the unassociated fools that try to cause trouble!). I was VERY impressed with the cornering ability of what has to be said is a wheeled barge!

However, as I was minding my own business being berrated by the girlfriend for my immature and potentially dangerous behaviour, I had to go past a bus. I waited for the opportunity and accelerated....

Normally its 1st 2nd 3rd quite quickly.. and this is where I think I might have caused my own downfall! I don't remember what gear I did or didn't get to! So I could have muddled my feet up or god knows what (That sounds REALLY poor and dangerous, but it is not the norm, I am just clutching at straws for an explaination!) Or more likely I could have not lifted and missed a gear!

What I am suspecting most though, as I had previously found problems, is that the mat MAY have slipped up enough to have prevented the throttle from springing back.

So.. Thats my sorry tail. As far as the car goes, it has only just been serviced, and it doesn;t use too much oil. I have been a bit lax, but its been less that 6 months and I have only dropped in half a litre to make me feel better (Its not been near the min mark but I would like it closer to the max!)

From Anders's description of the diesel engine and its working principles, it sounds like I have to be more worried about the fuel pump than the actual engine!

I don't think I have done anythign serious then. Currently it doesn't smoke and still pulls! On the plus side is was revved for only a split second, so I shuld be safe. I hope!

Unread post by **lolingram** » 27 Dec 2006, 21:06

Sounds very much like a runaway pump... this will wreck your engine if not attended to ASAP.

Often the only method is to kill the engine by putting into a high gear and drop the clutch. Only cure is to overhaul the pump. Good idea to change the cambelt at the same tme.

I have had it happen to my old 2.1TD XM, and seen it with a Merc diesel. The Merc engine let go big time as it sat revving away on garage fourcourt.... be warned.

Unread post by **CitroJim** » 28 Dec 2006, 08:57

If it has a Lucas Pump then air in the fuel lines can cause this problem. Air upsets the hydraulic controls of these pumps and can lead to just the sort of runaway you've experienced.

Lucas pumps do not give away air leaks in the same way as Bosch pumps do and so don't give the tell-tale starting difficulties.

steelcityuk · Unread post by **steelcityuk** » 04 Jan 2007, 20:56

At the very least get the mat fastened down before it kills someone.

Steve.