[GT_JT]

Hi folks, it's a sad day for my GT! My 2006 1.9JTD has been having MOT work done in recent weeks, part of which was to replace the inlet manifold as the flaps had reportedly broken which resulted in excessive exhaust smoke & the MOT fail. My mechanic phoned earlier to say the work was finished yesterday and the car was running really well during a test drive last night until the engine "ran away" and failed. I'd not come across this term before but after reading about it I understand the engine somehow finds another source of fuel and goes to extrememely high revs until it fails. I can't decide if the run away engine was in some way caused by the manifold replacement. Any ideas?

 

[pubsinger]

Unlikely IMO, as you say it's caused by some other source of fuel, often its own engine oil via failed turbo seals.

Could also be injectors uncontrollably overfuelling for whatever reason, however other than removing/replacing the high pressure fuel pump I can't think of anything fuel related that needs touching when swapping the manifold.

I suppose the high pressure pump could have started spraying diesel everywhere, but even then how would it have found its way into the engine?

What a bl00dy shame, I feel for you.

All the best, Pub

 

[Major_Clanger]

Oh no, that's awful....

The engine shouldn't be able to run away, even on its own sump oil, because the butterfly between the manifold and intake pipe will close, shutting off any air flow.

Double check the manifold was installed correctly. The engine can only run away if that butterfly fails.

 

[R.T.]

That’s what I thought but when I tried it I found that the throttle only closes after you key-off once the engine gets down to idle speed (at least on the 20 valve but I think the 16 valve is the same), so I fitted a ‘choke’ cable to the throttle so I could close it manually. Even without that the engine could almost certainly have been stalled by braking to a halt in gear. This only fails if it isn’t safe to stop, the clutch slips or through ignorance of it.

 

[Fruity]

I think pubsinger's first suggestion is correct. I blame turbo seals. The turbo seals can allow a certain amount of oil to pass (any diesel engine) and at higher mileage and if the car isn't taken for regular blasts, the oil can collect in lower parts of the boost system (intercooler). Then, if it is opened up a bit, the airflow can start to move the oil through in such quantity that it becomes the thing which is fuelling the engine. I think the only way out of a runaway engine is probably an empty autobahn until the boost system clears of oil (or the sump runs dry, if the turbo seals leak really badly).

If it is in a workshop, then pulling an induction hose (messy), or disabling the anti-dieseling throttle valve is the only way to prevent catastrophic damage. This should be a cautionary tale for others who should learn the emergency shut off procedure before they need to know how to.

What a shame.

 

[alfaitalia]

The anti shudder valve (also known as a shutter valve)is not designed to stop runaways.....and wont....they don't seal well enough and a diesel on full noise will easily pull enough air past it. They are there to stop the engine giving that old skool diesel shudder when switching off and also to create a small amount of vacuum by partially closing under certain conditions to help pull the air through the EGR valve....nothing more.
Pulling the intake hose off and using something strong but with enough flex to seal across the intake will stop it....but you need to be lucky to be able to do it fast enough to prevent damage. Never actually seen it happen (except online!)....but seen the result of one...a rod thrown through the block on a pretty early Golf diesel. Lady customer had massively over filled the oil....so the car run away on oil sucked up through the PCV valve.

 

[Major_Clanger]

The anti shudder valve (also known as a shutter valve)is not designed to stop runaways.....and wont....they don't seal well enough and a diesel on full noise will easily pull enough air past it. They are there to stop the engine giving that old skool diesel shudder when switching off and also to create a small amount of vacuum by partially closing under certain conditions to help pull the air through the EGR valve....nothing more.
Pulling the intake hose off and using something strong but with enough flex to seal across the intake will stop it....but you need to be lucky to be able to do it fast enough to prevent damage. Never actually seen it happen (except online!)....but seen the result of one...a rod thrown through the block on a pretty early Golf diesel. Lady customer had massively over filled the oil....so the car run away on oil sucked up through the PCV valve.

Really interesting and thought-provoking post, thank-you.

On that basis, is it worth getting rid of the butterfly to remove any restriction to air flow? Time to put a QR hose clip on the intake pipe I think.

 

[pubsinger]

If it is in a workshop, then pulling an induction hose (messy), or disabling the anti-dieseling throttle valve is the only way to prevent catastrophic damage. This should be a cautionary tale for others who should learn the emergency shut off procedure before they need to know how to.

When is it likely to happen in a workshop? Pretty rare I'd say. I would have thought the most likely situation is out on the road, with no assistance and no tools. I'm pretty handy under the bonnet but faced with an engine screaming and billowing smoke I think I'd be inclined to stay well away from it, far too much danger of injury.

If you were determined to save it I suppose you could slash the upper turbo hose...... if you kept a knife handy. But then think of the trouble you'd be in if you were ever stopped and searched by plod. "Erm, it's in case I have to slash my upper turbo hose ociffer", can't see that cutting much ice.

All the best, Pub.

 

[R.T.]

I think I’ll stick with my ‘choke’ cable thanks and do it from the comfort of my seat.* I confess I haven’t had to use it in anger but it easily stops the engine from 4000 revs no load.** At ‘full noise’ there would be more air flow and pressure but so long as it didn’t break, which I judge to be improbable, it would do the job.

To try to answer the original question – removing the manifold requires the breather system to be dismantled to some extent, and that part of it contains a valve which is supposed to stop sump oil being sucked into the engine. Even if disturbing the valve caused it to choose that moment to fail it would still require something to block the air intake and create the suction needed to suck the sump oil up. A blocked air filter or road debris in the intake possibly.

The other source of fuel, the turbo seal is nothing to do with the inlet manifold.

So from a distance I can’t see that the manifold job is connected with the failure, but if the engine or parts of it are to be recovered I would check the breather system, air filter and turbo.



* Original thread: JTD Run-away



** Don’t actually stop the engine, let it idle first or you will leave the turbo spinning without an oil supply.

 

[Major_Clanger]

I've been thinking about the runaway scenario and am troubled that the anti-shudder butterfly won't stop the engine. In the unlikely event this happening I'm considering this QR hose clip, assuming it can seal properly. If I can pull then hose off quickly then my palm across the throttle body must surely be good enough?

Being next to a runaway isn't pleasant..... I had to once with a big long-stroke 3-cyl Kelvin (marine engine). That certainly concentrated the mind; all I could do to stop it was hold the decompression lever up and hope it didn't put a rod in to me!

 

[alfaitalia]

I reckon that would hurt a hell of a lot...if it didn't suck your skin straight off! Hurt me enough when I got my hand too close to a 1.3 Mk2 Escort carb....and that was only ticking over!

 

[Major_Clanger]

I reckon that would hurt a hell of a lot...if it didn't suck your skin straight off! Hurt me enough when I got my hand too close to a 1.3 Mk2 Escort carb....and that was only ticking over!

You really think it would be sucking that hard? Presumably without air it would die pretty quickly.

 

[alfaitalia]

I think so......don't forget the the rev limiter/governor wont work so it will rev over the red line....but let's say it's a 2 litre derv at 5000 rpm...that's over 80 litres of air per second....that's a, serious vacuum..but equally I think we are getting people worried about something that most people have never even heard of....it's certainly not something I worry about on my old girl. Dont overfill the oil, look after the PCV, keep an eye out for the tell tale blue smoke under power that warns of a turbo reaching the end of its life and sucking oil through to the compressor side.....and is extremely unlikely to happen. As I said...I heard of one in all my years in the trade...and the owner had severely over filled the oil.

 

[Nitram]

Witnessed a runaway diesel once at a motorway services, Cavalier if I recall correctly. Told the driver to stand on the brakes and let the clutch up in top. It stopped it ok. However it had been running a bit before he did it so not sure what damage resulted.

 

[R.T.]

I've been thinking about the runaway scenario and am troubled that the anti-shudder butterfly won't stop the engine.


What’s your concern?

What’s bugging me is why Alfa programmed the throttle to behave like this, apparently VW close it when you key-off regardless of engine speed, and it stays shut until the engine stops. Conceivably, if the engine was used for braking with the key off on a long hill enough oil might be pulled past the valve guides to cause a brief runaway at key-on. This seems like a weak argument though because the instinctive reaction would be to turn off again, which would regain control. Perhaps Alfa were just worried that the pressure spike on closing the throttle might split the boost hoses?

If it does ever happen to me I’m going to close the throttle slowly and I suspect that once the airflow and turbine speed were sufficiently reduced the oil would no longer be carried through the inter-cooler and into the engine, allowing me to drive very gently to a safe stopping point. If not I’ll just have to shut the engine down and coast. If it happens - I’ll let you know if I’m talking rot (promise).

[ps: Taking the boost hose off? Not for me, too slow and too messy. But if I was unlucky that might be the least of it. At full chat I imagine the turbo would mix the air and oil into a nicely combustible and hotish mixture. If there happened to be a source of ignition within range (10-15 foot?) I would be left holding a flame thrower. Dropping it (naturally) would with the inevitably of fate on a bad day result in it falling back into place, but with half the hose exposed. The lower half would feed the engine nicely preheated fuel while the upper half continued to bath the surrounding area in flames.]

 

[johnnyroper]

Best way to try and save engine is top gear,foot jammed on brakes and let clutch out. By time you have popped bonnet,got out,pulled bonnet up,removed hose and stopped air intake a diesel full chat sucking oil up I suspect your efforts will be too late to save it.