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Saw this and got scared
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10-28-2011, 07:05 PM | #1 |
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Saw this and got scared
I was perusing the net and, naturally, I came to a BMW forum, I think it was BMW Land or something... Anyway, the thread was about when a turbo blows on a diesel engined car (the N57 in this case) and how it completely destroys the whole engine. I read on...
It said that the turbo lets go and the oil supplying the turbo goes through the boost pipe, is turned into a vapour and then goes in the cylinder and is auto-ignited which makes the engine rev like mental and shortly explode. Fine, but this is where I got scared - YOU CANNOT TURN THE ENGINE OFF!!! You can hit the stop button, take the key out but it will not stop the engine until it explodes!! The only way to cease the over revving is to open the airbox and block it, starving the cylinder of oxygen. If you have a manual, you could try stalling it but if its an auto (attention 35d owners) you\'re probably stuffed. Apparantly the signs of the turbo(s) letting include excessive whistling and whining, so if your car is doing this, I advise strongly against running it. However, I would like to know a little more information about this such as how high the engine rev\'s and why no cut off to the cylinders is available on turbo diesels. Here is a video of an N57 X5 dying through the aforementioned cause. http://www.youtube.com/watch?v=58SoI7YKr4o
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10-28-2011, 09:13 PM | #3 |
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That may have been an earlier N57 or even an M57, but all current production M57s (the M57Y in North America) and N57s in fact have a throttle valve; not to perform fuel metering, but to perform multiple functions including restricting intake air flow to raise EGTs for a DPF regen cycle, to act as an anti-shudder valve during shutdown, and to act as an emergency shutdown should the engine begin running away due to uncontrolled ingestion of a flammable material like turbo oil, etc...
Regards D.
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10-28-2011, 11:17 PM | #4 |
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First post for me, new 335d owner. Glad to hear that there are mechanisms to prevent runaway diesel engines. This happened to me in Germany years ago. We were driving an M757 tractor on the autobahn. This is an 8-wheel driver cab over tractor for Pershing Missile Erector Launcher. Turbo diesel with a 6 speed auto trans.
Suddenly the 757 was accelerating, not responding to off throttle and fighting the brakes. Just running away. So my buddy pulled into a rest area and put the tractor up against a stone wall and put it into to neutral. The engine was just screaming. I jumped out and grabbed a crescent wrench and disconnected the fuel line and the engine starved out and stopped. Had to have tow a into motor pool about 50 clicks down the road. I was really happy that the rest stop had a wall. I'd hate to try to do this on a 335d. BTW, this is a great site, I've read a few threads and very informative. |
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10-29-2011, 07:58 AM | #5 |
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Ahh well that puts my mind at rest! Glad to hear there is a cut-off.
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10-30-2011, 11:11 AM | #6 |
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I've seen this happen before on the dyno. This was an older engine at a vocational school. This particular setup didn't have an intercooler, I can't recall if it was because it was on an engine dyno and they didn't have a way to plumb it in or if that motor just didn't have one. It also had a failure in the mechanical governor that caused it to run away not a turbo failure.
The first thing handy was a shop manual so, they tried to block this intake with it. Unfortunately the placement over the intake wasn't the best and it began ingesting one sheet after another, shredding, burning and ejecting out charred shreds of paper out of the exhaust. It was enough to slow it down to where it wasn't going to blow and to find a piece of sheet metal to completely kill it. Terrifying and hysterical all at the same time. Regarding why there is no shut off in this situation it's simple since a diesel auto ignites as long as it can ingest air and fuel it will keep running. In the past with mechanical injection there was no way to shut the off the fuel outside of the governor. Now with piezo electric injectors you can shut the fuel off but, if it were to find an alternate fuel source like finely atomized oil it could continue to run. I say could because I don't think it's that likely to happen as all that oil has to travel through the IC where most of it will likely be trapped and the engine will stall. With the throttle valve you can also address the concern of it being able to find an alternate fuel source in the worst case scenario by choking the air supply. Last edited by hotrod2448; 10-30-2011 at 11:19 AM.. |
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11-01-2011, 08:05 AM | #7 |
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I've seen tons of "runaway diesel" videos on YT; but I'm glad to hear the newer designs take care of that problem. I'm guessing the throttle plate is not actually controlled by the throttle input, but it's something that the ECU controls transparently.
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11-01-2011, 12:07 PM | #8 | |
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Quote:
http://en.wikipedia.org/wiki/Valvetronic |
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11-02-2011, 06:25 AM | #10 | |
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Quote:
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11-02-2011, 01:37 PM | #11 |
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Apparantly the 330d was most prone but I think the new version like mine has all the cut off crap
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11-06-2011, 07:21 PM | #12 |
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Damn, and I just got my first SES light and I am 70 miles from my dealership.
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11-07-2011, 01:43 AM | #13 |
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Dayyum! Whats up with it? I don't think it'l run away :P
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11-07-2011, 10:24 PM | #14 |
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Well, I am hoping it is just a stuck valve on the DEF system, but I dont feel like paying the stealer for a scope, so I am going to take my chance, wait for money to transfer to my paypal account and pickup cable on ebay and start reading codes to find out what is wrong, so in two weeks I should find out. The SES light went away for a little while this morning, but came back soon. Car has over 71k miles and I did not get the extended warranty, so I am on my own.
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11-09-2011, 06:27 PM | #15 |
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I would be interested to know when the runaway diesel syndrome was solved in BMW. This was my only concern when buying a Diesel, I didn't even know it was solved!
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11-10-2011, 02:05 AM | #16 |
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wow. and all this time they were checking brakes at all the truck stops?
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