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Old 26-02-2012, 15:12   #1
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Diesel Runaway or Overspeeding

Hey folks, since I'm in the middle of dealing with my little runaway (the joke I heard is that there is no such thing as engine runaway... it's actually mechanics runaway when dealing with "overspeeding").
I was having a hard time getting a clear picture of the the why and how so I could diagnose the cause properly. There is plenty of info it is just scattered all over the place including here and several other sites.
This post is my own amature attempt at a diagnosis protocal.
My goal here is to try to give someone a decent one stop chunk of info that will help them solve the problem as cheaply and effectively as possible. Please chime in if you see any ommissions or problems
Based on various forum comments and conversations with mechanics this is mky best shot:

1. Make sure not to overfill oil. Oil overfill can cause blow-by of engine oil into the cylinder heads. Once (if) the overspeeding engine has been stopped allow engine to settle then check the oil level in the crankcase. Drain off excess oil as needed and while your at it change the oil if it‘s dirty. If the engine oil level is normal or excess has been drained try again to turn over the engine the following day.

2. Had the engine RPMs been fluctuating or “hunting” ; suddenly increasing then dropping again prior to the runaway? This could indicated either a partially clogged fuel filter or bad fuel line connection inhibiting proper fuel delivery. It can also be a symptom of a screwed up injector that can become stuck open allowing fuel to spray uninhibited into the cylinder thereby causing runaway. In the case of those engines with the injectors racked together all injectors will be frozen in the open position. Let the engine cool down, check all fuel line connections, change the fuel filter(s), bleed the system, try again to see if the engine RPMs are still fluctuating. Next step will be to check if one of the injectors is having a problem. Remove each injector one at a time if possible and crank the engine. Each injector should pulse and not allow a steady stream of fuel. Replace/rebuild any defective fuel injectors and try the engine again. The threat of runaway should be incentive enough to attend to fluctuating rpms promptly. I knew it was fluctuating on my Perkins but did not understand the importance of trying to fix it sooner than later.

3. The governor in the injector pump has failed and the injection pump has to be re-built.
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Old 26-02-2012, 15:25   #2
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Re: Diesel Runaway or Overspeeding

As a young soldier I watched a main battle tank engine run away in the workshop. Mechanics were running for their lives, but one brave sole climbed on board and armed with nothing more than a 1L Halon fire extinguisher shut it down and saved us all a lot of clean up work even thought the engine was scrapped.

CO2 or the Halon replacement gas on a yacht would be as effective.

Pete
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Old 26-02-2012, 15:30   #3
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Re: Diesel Runaway or Overspeeding

With turbo you can have a runaway from bad seals and oil leaking. That one happened to me.
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Old 26-02-2012, 15:34   #4
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Re: Diesel Runaway or Overspeeding

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As a young soldier I watched a main battle tank engine run away in the workshop. Mechanics were running for their lives, but one brave sole climbed on board and armed with nothing more than a 1L Halon fire extinguisher shut it down and saved us all a lot of clean up work even thought the engine was scrapped.

CO2 or the Halon replacement gas on a yacht would be as effective.

Pete
We used to ground hop packs before we put them back in tracks in the army. I was a diesel mechanic in a 3rd shop setting. We always made sure when we started the pack to make sure someone had a clipboard ready to put over the air intake if it started running away. Had a bunch of new troops on my contact team. So I handed one the clipboard and gave him instructions on what to do if the pack ran away. We started the pack an 8V-72 Detroit Diesel. It immediately started to runaway. When I turned to look for the kid with the clipboard he had run away too. Found another and went and slapped it over the intake. By this time you couldn't see a thing.
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Old 26-02-2012, 15:36   #5
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Re: Diesel Runaway or Overspeeding

Is this a 2 cycle diesel? I was under the impression it was 2 cycles that primarily had the runaway issues. Almost always came back to valve timing and adjustment.
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Old 26-02-2012, 15:48   #6
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Re: Diesel Runaway or Overspeeding

Yes, ours were, Leyland 2 stroke opposed piston design, used in buses but hopeless in a tank, right piece of junk.

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Old 26-02-2012, 18:54   #7
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Re: Diesel Runaway or Overspeeding

Mine is a Perkins 4107 and the consensus from all sources including pro mechanics was a broken governor and that I needed to have the injector pump re-built... turns out to not have been the problem. Ah well, $450.00 tuition for learning more about the problem, how to pull a pump and put it back on.
Seems from what I read that it is more likely to happen with older two cylinders but can still be a problem for any diesel.
Apparently there was a big refinery disaster in Texas once that was caused by an exploding runaway diesel that was idling and sucking in the hydrocarbons just from the air. I've heard that the rule now is that all diesel trucks comming into a refinery have to be towed around.
Another story from a local here was that in the course of overhauling his engine he has used a solvent gun to clean out the block when he reassembled it and turned it over it took off. Apparently there was enough solvent left in the block to fuel the runaway.
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Old 26-02-2012, 20:09   #8
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Re: Diesel Runaway or Overspeeding

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Seems from what I read that it is more likely to happen with older two cylinders but can still be a problem for any diesel.
Not two cylinders, two cycle diesel engines. Two cycle diesel engines have air intake ports in the bottom of the cylinder. They use super chargers or turbo chargers to blow air into the bottom of the cylinder and exhaust out the other side. Because of this if they are over filled with oil the intake air can pick up oil from the crankcase. With this oil in the intake air the diesel runs away. I have never heard of a four cycle diesel running away. Not saying they couldn't.

Brad
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Old 26-02-2012, 20:27   #9
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If a diesel gets a big enough sniff of a volatile hydrocarbon source (gasoline, ether, acetone, etc) then a runaway is a distinct possibility. If left unchecked the overrunning engine will eventually start consuming its own lubricating oil.

The common method of dealing with it was to block the inlet with a flat board to restrict the air flow. (Diesels are fuel regulated whereas IC engines are air regulated) Had it happen to some old stationery engines but can't recall any cases in recent years.
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Old 26-02-2012, 20:40   #10
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Re: Diesel Runaway or Overspeeding

A rubber ball the right size will stop a Perkins dead in it's tracks !! Just a thought ! Bob and Connie
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Old 26-02-2012, 20:57   #11
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The only thought I have is that if the engine is running stable at idle, crack each injector nut one at a time to see if you have a dead cylinder/injector. Its a bit messier than cracking and cranking but a bit quicker.
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Old 01-03-2012, 23:25   #12
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Re: Diesel Runaway or Overspeeding

4 cycle diesels runaway just fine. I have had it happen twice. Once on a Perkins 4-154, caused by a pinhole in the lift pump diaphram that filled the sump with fuel, and once on a Caterpillar that hadnt been run in a few years and the rack stuck at full speed. VERY SCARY. I used to work on a power boat that had a pair of old GMC 6-110s that had an air shut off system between the air filter and the engine, just in case the engine ran away. It is a more common problem than people realize. Faulty lift pumps are usually the reason. _____Grant.
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Old 01-03-2012, 23:42   #13
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Re: Diesel Runaway or Overspeeding

Older mercedes diesels(four stroke) had vacuum governors. I think I remmeber a big leak in the plastic vacuum line would make them race. Duct tape can fix it for a few years.

I made mine run backwards once by rolling back out of a driveway and popping the clutch in forward gear. A flapper valve is supposed to prevent that but it was loose.
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Old 01-03-2012, 23:45   #14
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Re: Diesel Runaway or Overspeeding

Quote:
Originally Posted by Butler View Post
Apparently there was a big refinery disaster in Texas once that was caused by an exploding runaway diesel that was idling and sucking in the hydrocarbons just from the air. I've heard that the rule now is that all diesel trucks comming into a refinery have to be towed around.
I am from Texas and was born and raised in what was the oil & refinery capital of the world. I am LMAO about the above. Think about what you have posted..."hydrocarbons in the air." Ha, ha, ha!!!

And think about your towing scenario...if it was true, they would be towing all trucks entering because they are all diesel...and what do you think they would be towing these trucks with...electric cars???

Well, anyway, just goes to show you that most people have no idea what Texas really is.

Bill
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