Uncontrolled revving - PeachParts Mercedes-Benz Forum

troutmaster4 · #1 08-12-2010, 06:22 PM

I have a 1985 300SD Mercedes turbo diesel that is running wide open when started and dash switch won't shut it off. Have to pull fuel line to shut it down! I had inj pump worked on and appears to be ok, have not had it tested yet.
the fuel rack position sensor connects to the control unit and so does the switch over valve that controls air recirculating valve. Do they interact in some fashion from the control unit? Would a defect here cause uncontrolled engine reviving?
Anyone have any other ideas what to check? I am grasping at straws now.

1979300sd · #2 08-12-2010, 06:24 PM

that sounds to me like runaway diesel syndrome, although pulling the fuel line wouldn't shut it down I don't think...

Fulcrum525 · #3 08-12-2010, 06:25 PM

Quote:

Originally Posted by troutmaster4

I have a 1985 300SD Mercedes turbo diesel that is running wide open when started and dash switch won't shut it off. Have to pull fuel line to shut it down! I had inj pump worked on and appears to be ok, have not had it tested yet.
the fuel rack position sensor connects to the control unit and so does the switch over valve that controls air recirculating valve. Do they interact in some fashion from the control unit? Would a defect here cause uncontrolled engine reviving?
Anyone have any other ideas what to check? I am grasping at straws now.

DO NOT START IT AGAIN UNTIL YOU READ THIS THREAD!!!!!

Run away diesel, why does it happen?

OR

Anyone ever have a runaway diesel?

(There are others as well)

Beastie · #4 08-12-2010, 06:33 PM

What dash switch ? I have an 85 300SD and there is nothing on the dash that I am aware of. There is the emergency cut shut down/off under the hood. Is that what is not working ?

Beastie · #5 08-12-2010, 06:36 PM

If it is an 85 and any work has been done look at all vacuum connections on the driver side of the engine. Apparently from many+++++++ on this post this happens often. I know !

kerry · #6 08-12-2010, 06:45 PM

Why did you start a second thread on this issue when lots of people gave perfectly good advice on the original thread?

Engine runs wide open

troutmaster4 · #7 08-12-2010, 07:15 PM

My 300Sd still runs away when started! I was told an open container of gas or a drip pan under engine w/aircleaner and horn off could cause this. So I cleaned up and have good cross ventilation in garage. But no difference. It will shut off after I pull filter off fuel line but not till abt 10'15 agonizing seconds. Maybe these engines are bullet proof or idiot proof after all. Don't know why it hasn't thrown a rod or timing chain from the high reves.
Inj. pump is off again and going back to shop for further testing. Acts like govenors working, pump govenor that is not Pa govenor Ed Rendell. Well same difference.
I will use the board over the intak of turbo charger next time!
Thanks

panZZer · #8 08-12-2010, 07:18 PM

Take the shut off valve off you had someone install and reinstall it correctly - The spring has to be connected to it correctly

kerry · #9 08-12-2010, 07:43 PM

Quote:

Originally Posted by troutmaster4

My 300Sd still runs away when started! I was told an open container of gas or a drip pan under engine w/aircleaner and horn off could cause this. So I cleaned up and have good cross ventilation in garage. But no difference. It will shut off after I pull filter off fuel line but not till abt 10'15 agonizing seconds. Maybe these engines are bullet proof or idiot proof after all. Don't know why it hasn't thrown a rod or timing chain from the high reves.
Inj. pump is off again and going back to shop for further testing. Acts like govenors working, pump govenor that is not Pa govenor Ed Rendell. Well same difference.
I will use the board over the intak of turbo charger next time!
Thanks

Read your original thread. There's more than one post that points you towards an incorrectly installed shut off valve.

MBeige · #10 08-12-2010, 08:55 PM

The shutoff solenoid has a hook at the end that goes into the injection pump. This hook is supposed to PULL on a lever in the injection pump to shut it off properly. If the solenoid was installed incorrectly, meaning the hook would actually PUSH instead of pull, then you've got a run away scenario.

Tug gently on the solenoid when you install it to ensure it is hooked up properly. You should feel resistance if the hook is installed correctly then from there maintain the tension and install the "base" of the solenoid to the back of the IP with the proper washer.

Diesel911 · #11 08-13-2010, 12:59 AM

Quote:

Originally Posted by troutmaster4

My 300Sd still runs away when started! I was told an open container of gas or a drip pan under engine w/aircleaner and horn off could cause this. So I cleaned up and have good cross ventilation in garage. But no difference. It will shut off after I pull filter off fuel line but not till abt 10'15 agonizing seconds. Maybe these engines are bullet proof or idiot proof after all. Don't know why it hasn't thrown a rod or timing chain from the high reves.
Inj. pump is off again and going back to shop for further testing. Acts like govenors working, pump govenor that is not Pa govenor Ed Rendell. Well same difference.
I will use the board over the intak of turbo charger next time!
Thanks

The reason it has not thrown a Rod "Yet" is because there is an adjustment on the Governor (if done correctly) that after it gets above a certain RPM it will limit the Engine speed.

More advice.
I have read that if the Rack Damper Pin is turned in too far it will also cause a runaway. But, that should be in tha " Causes of a Runaway Engine" thread that Hunter posted.

troutmaster4 · #12 08-13-2010, 05:32 PM

My thanks to all who replied to my questions, I have been posting this question on multiple help sites, sorry for the re post of the same question.
I am taking the injection pump back to the garage that worked on it and have them check it out, something is not working.
I may be back with more questions, I truly appreciate all of your answers.
It is good to know there are people out there that know a lot more than I do and are willing to help others.

kerry · #13 08-13-2010, 05:37 PM

It's a lot of work to remove the pump and take it to the shop. Why don't you just remove the shut off valve and make sure it is installed correctly? That's much easier than removing and installing the IP.

troutmaster4 · #14 08-14-2010, 08:29 AM

I have had the inj pump on and off before and just wanted to have the garage check the work they did, that they didn't miss anything or put something back together wrong.
Everything looks & acts normal. Linkage works ok, moves freely from stop to idle adj screw. Only linkage that was removed is the down rod from bell crank to inj pump arm. Return spring hooked up and hooked on vac shut off valve was engaged in slot on control rod. Any way, pump is back to shop and will post new findings or new concerns when I get it back.
This condition is a real mystery to me but I really learned a lot about Mercedes such as the square metal "thingy" to ALDA valve & understand why it's there and how it works and a lot more.
I still love my Mercedes even though it has not moved in 2 months. It has nearloy 300K on it. I have owned it for 2 years. I am the 6th owner. PO's or their mechanic have tinkered with it. Switch over valve bypased, ALDA "adjusted", inj. pump has been off before, etc.
Thanks again to all the help you have given me. Maybe we will figure this one out. Everyone loves a mystery

cirrusman · #15 08-14-2010, 01:32 PM

Quote:

Originally Posted by troutmaster4

Maybe these engines are bullet proof or idiot proof after all. Don't know why it hasn't thrown a rod or timing chain from the high reves.

Wanna see how hard to kill is your engine? Check this out:
http://www.youtube.com/watch?v=wTdC3LC2lW0&feature=player_embedded
These creeps were having a tough time killing that poor Benz...