1981 300 SD engine runs full blast!

[maximumbob]

6-13-06

I really need some help as I reinstalled a new vacuum control unit on the side of the IP (not the valve on top of the IP) for the second time as it wasn't shutting the engine off the first time I installed it. I obviously did not do it right the second time either as the engine ran full bore, until out of sheer fright and ignorance, I opened an injection line to one of the cylinders. I just don't know if the engine shut down because of lack of fuel...or it blew.

Now I am afraid to reinstall according to the great post on this thread as I now also know I didn't hook up all the vacuum lines right, or forgot to hook one up, believed to be the one on top of, or lower one, going to the vacuum control valve that sits on top of the IP. I've seen most of the schematics but am not positive that I have the right one. Could an incorrect installation of a vacuum line, or failure to install a vacuum line, also cause the engine to run full bore?

Need to know: (1) the correct vacuum schematic for my model, (2) if a problem with the vacuum lines could have caused the engine to run all out, (3) how to tell if the engine is still good before I start it, (4) the easiest/fastest way to shut down the engine should I screw up again, (5) will the shutoff push lever shut it down, (6) does the lever from the vacuum control unit that hooks inside the IP work the external linkage/lever or the rod it may attached to inside the IP by affecting the fuel flow?

I've let my MB parked in the driveway for two weeks afraid to do anymore until I am able to get some answers form you experts. Amazing what should have been a simple installation has turned into a nightmare.

Please help. I can also be reached during the day at 210-208-6629.

Bob Brown

[Maroon 300D]

It would seem that you didn't install the IP shutoff valve correctly; this has been known to cause a runaway engine, which is the condition you describe.

From what I've read, the best way to shut the engine down when it's running away is to cut off the air supply. Cutting off air or fuel will stop it (unless it's overfilled with oil - then it can run on the oil if you are trying to stop the fuel supply. That's why I think cutting off the air supply, when you can, is better). When you think you have the IP shutoff valve right and want to try it out, take the air filter out and be ready to put a large block of wood up against the air intake so as to stop the engine from getting air. This should shut it down in a hurry. Spraying a fire extinguisher into the intake would also stop it, or so I've read.

I have no direct experience with a runaway engine (and hope to God I never do!), but it sounds like there's a very good chance you saved it. If it stopped after you disconnected the fuel line and you didn't hear any terrible sounds, I'd guess it will work. I don't know of any method of testing it without running it.

I've seen an excellent write-up on how to install the IP shutoff valve somewhere on this site. I recall that the guy posted it on two different threads, but I can't remember what they are called.

A user named 'Phantoms' posted a lot of great vacuum schematics; I'm sure one of them applies to your vehicle. In your case the shutoff valve itself must be the problem, though, I really doubt it's a coincidence that you installed it and this happened.

Hope this helps and best of luck!
May your car ride another 200k at least.

Edit: looking at your post again I guess I'm a little unclear on what you were installing. Is it indeed the shutoff valve? Also, the stop lever won't work with a runaway engine.

[sixto]

Have someone hold the block of wood against the turbo inlet when you start the engine. There should be enough air to get it started but not let it run for too long if the shut off valve isn't installed properly.

You can go as far as starting the engine with the shut off level all the way down. It shouldn't start. That should be some confirmation. If it starts, the block of wood won't let it go far.

Myself, I use a mouse pad.

Sixto

[Strife]

I read somewhere (maybe here) that truck diesel mechanics keep a carbon-dioxide based fire extinguisher handy for runaway truck engines, which is shot right down the intake. A runaway truck diesel is supposed to be really dangerous, with flying parts and chunks of metal involved, never mind the expensive damage.

"Spraying a fire extinguisher into the intake would also stop it, "

Do NOT use a standard Dry chem ABC fire extinguisher into the intake. It will kill your engine, in the bad way. The dry stuff will get inside the engine and act like dirt would on the cylinders. The only fire extinguisher that can be safely used on an engine is a CO2 model.

Also, don't put your hand over the intake to try and stop it. It will only hurt you really badly.

CO2 link
They are not cheap, but it's less than getting a new engine.

[SD Blue]

Try here:Replacing the Injector pump shut of valve and preventing a run away engine