Did a valve adjustment and my engine ran away!? - PeachParts Mercedes-Benz Forum

BodhiBenz1987 · #1 06-10-2009, 06:42 PM

... I just did my first valve adjustment on my 78 240D, and everything seemed to go OK. I was really careful and followed every step according to the Haynes manual and the dieselgiant tutorial. I put everything back together, tightened the valve cover down to spec and went to start it up. It immediately roared to max rpm, so I turned off the key (no response to that) and hit the stop lever. It shut off with the lever. I don't have a tach but it sounded about the speed if I were flooring it. Nothing smoked or clunked or came flying off, but it scared the living ^$&* out of me and I'm terrified to even think about starting it up again. Is there anything I could have done wrong with the valves that would cause this? This was my first adjustment and it seemed straightforward but god knows what I could have done.
Two other things I thought:
-Did I maybe bend or bind the throttle linkage ... could that cause this to happen? It looks fine to me and looks like it moves, but maybe it's in the wrong position somehow?
-Could this have been something that just happened to fail now? The car sat for four days without being started, and when I went to unlock it, the locks didn't work. I thought maybe the car just hadn't held vacuum over those days. The last time I drove it it ran, shut off and locked just fine. After the mini-runaway, I went back inside and when I went to lock it, the locks did work, but very, very slowly. Shouldn't it have built up the vacuum in that episode? Do I maybe have some other vacuum issue that it randomly developed while sitting four days?

Ideas please. I really don't understand this, and I'm afraid to even touch the car again. After all this I really don't want it to die.

patbob · #2 06-10-2009, 06:46 PM

Any chance you reconnected the linkage wrong? Or didn't reconnect all of it? That'd be my first guess since the shutoff lever stopped it. Also, since it didn't accellerate until it exploded, it was probably being saved by the govenor in the IP, which futher suggests it wasn't a true runaway. Scarry just the same through.

You might have a vacuum leak too, but that wouldn't cause it to rev. Not shut off yes, rev no. Unless the cruise control got in on the fun somehow (don't some of them use vacuum to help push the linkage around?).

DieselAddict · #3 06-10-2009, 06:50 PM

Throttle linkage is the first thing that came to my mind. Make sure it moves freely without sticking throughout the whole range and is properly connected. I've read that on these cars (assuming you're talking about one of your 240D's) these things happen if you mess with the vacuum shut-off valve, but simply disconnecting it shouldn't cause a run-away condition.

BodhiBenz1987 · #4 06-10-2009, 06:50 PM

Quote:

Originally Posted by patbob

Any chance you reconnected the linkage wrong? Or didn't reconnect all of it? That'd be my first guess since the shutoff lever stopped it. Also, since it didn't accellerate until it exploded, it was probably being saved by the govenor in the IP.

I don't think I could have really connected it wrong, since I only had to disconnect two joints ... I just left the rest on top of the valve cover sitting off to the side. I'll double-check.

Mike D · #5 06-10-2009, 06:51 PM

Which car? If it's on the W123's then you either broke the plastic line leading to the vacuum solenoid or left it off/loose. You have to remove the line to pull the valve cover. That will cause the car not to shut off.

If it's the W115 then the same thing regarding the plastic line only this one controls the regulator for the injection pump.

tbomachines · #6 06-10-2009, 06:52 PM

My first thought is that you might have connected the linkage incorrectly. Perhaps you switched one of the longer shafts for a shorter one and vice versa--this could possibly lead to it thinking its WOT.

edit: nevermind, beat me to it!

BodhiBenz1987 · #7 06-10-2009, 06:52 PM

Quote:

Originally Posted by DieselAddict

Throttle linkage is the first thing that came to my mind. Make sure it moves freely without sticking throughout the whole range. I've read that on these cars (assuming you're talking about one of your 240D's) these things happen if you mess with the vacuum shut-off valve, but simply disconnecting it shouldn't cause a run-away condition.

Yes, this it the 78 240D, I meant to mention that. The shut-off valve crossed my mind but I wasn't sure if this was a typical way for it to fail ... i.e., everything was normal last time I drove it and parked it, and then just suddenly on start-up it goes bonkers. Guess I'll do a search and read some horror stories.

BodhiBenz1987 · #8 06-10-2009, 06:55 PM

Quote:

Originally Posted by Mike D

Which car? If it's on the W123's then you either broke the plastic line leading to the vacuum solenoid or left it off/loose. You have to remove the line to pull the valve cover. That will cause the car not to shut off.

If it's the W115 then the same thing regarding the plastic line only this one controls the regulator for the injection pump.

I did not remove that during the adjustment ... will check it. Wouldn't it just cause the car to not shut off, as opposed to cause it to go to full throttle? I knocked the vacuum line off my 300D once and it idled normally, just didn't stop with the key.

BodhiBenz1987 · #9 06-10-2009, 07:09 PM

OK, just went and took another look. The vacuum line looks fine ... and it's pretty much clear of the engine and valve cover, unless I'm looking at the wrong thing? I also was able to move the throttle linkage smoothly and it looked like it was normal movement. It looks like it's in the normal off position when left untouched. I guess it's possible when I reattached it, it got stuck slightly and then maybe unstuck once I hit the stop lever and then moved it by hand. I didn't think to check for range of motion right after I reconnected it. However, I'm afraid to try starting it to see if it works correctly now. I was relieved the stop lever worked the first time, but I know if it is the shutoff valve, the lever may not work next time.

DieselAddict · #10 06-10-2009, 07:18 PM

Make sure the throttle linkage is well lubed and doesn't get stuck when you press the gas pedal. The fact that you can stop the engine with the stop lever tells me that your shut-off valve is probably OK. If you had a true run-away condition, only starving the engine of air or self-destruction would shut it off. Perhaps have a fire extinguisher handy the next time you try to start the engine just in case.

BodhiBenz1987 · #11 06-10-2009, 07:25 PM

Quote:

Originally Posted by DieselAddict

Make sure the throttle linkage is well lubed and doesn't get stuck when you press the gas pedal. The fact that you can stop the engine with the stop lever tells me that your shut-off valve is probably OK. If you had a true run-away condition, only starving the engine of air or self-destruction would shut it off. Perhaps have a fire extinguisher handy the next time you try to start the engine just in case.

Yeah I haven't been able to find a CO2 extinguisher, maybe I'll go hunting for one tonight. I don't think I could undo all the injectors in time. Guess I can also take the hose off the air cleaner for easier chokage access in the event of emergency.

Am I correct in my thought that this wouldn't be caused by error in the actual adjustment of the valves? I just want to rule that out.

Lexxani · #12 06-10-2009, 07:35 PM

bodhi-

listening to the aftermarket manual was definitely your first mistake (get the FSM!!!!). A search should have been done and if that didnt yield what you were looking for answer wise then start a thread. That said...

I tend to think a linkage error, like everyone else has said. I do not own a 240, but have looked at enough ones to think that is the most likely culprit. A misaligned valve would have yielded a "no start" situation or at best a "poor run" situation.

You post quite a bit, and from my deduction know enough about these things to have not made an amateur mistake, but we all have our "moments"....

Check that linkage and the rubber line to the silinoid and im sure you will kill two at one once...

Good luck, we are here for you...

BTW, this is why pre '76 M117 engines rock, hydraulic compensators!

DieselAddict · #13 06-10-2009, 07:43 PM

Quote:

Originally Posted by BodhiBenz1987

Yeah I haven't been able to find a CO2 extinguisher, maybe I'll go hunting for one tonight. I don't think I could undo all the injectors in time. Guess I can also take the hose off the air cleaner for easier chokage access in the event of emergency.

Am I correct in my thought that this wouldn't be caused by error in the actual adjustment of the valves? I just want to rule that out.

I don't think bad valve adjustment would cause that though I suppose it could cause oil to leak into the cylinder(s). But if that was causing your run-away condition you wouldn't be able to shut the engine off with the stop lever. You also wouldn't be able to stop it by disconnecting the injectors if the engine was running on oil. Hence the only reliable way to stop a true run-away condition is to choke off the air supply, either with a solid object or fire extinguisher. Don't use your hand, you might lose it.

barry123400 · #14 06-10-2009, 07:46 PM

It is quite reasonable to assure you that the actual adjustment of the valves could not in itself cause this problem. Get set up to smother the intake before you restart just in case some issue exists.

Make sure the throttle linkage is at the minumin position. There is a very slight chance although I do not know how. You have somehow reversed the linkage. So now the idle position is instead now the wide open position. At the idle setting the arm on a 240d injection pump should be about the 1 to 2 oclock position when looking at it from the otherside of the engine.

Another way of expressing it. Pump arm should be about 20 to 25 degrees above a horizontal line going through the shaft on the injection pump lever arm. If the arm is lower than the centerline of the shaft thats your problem.

The worse possible senario is that something may have gone wrong inside the pump itself when removing or installing the linkage. Thats why I suggested to remove the air cleaner and be prepared to smother the engine if required. Although the govenor if still working will limit the revs.

BodhiBenz1987 · #15 06-10-2009, 07:49 PM

OK, I did a search of throttle linkage binding, and saw the suggestion to disconnect the linkage at the throttle lever ... it should then idle normally. What do you guys think ... should I grit my teeth and try this?

Looking for a big flat piece of wood to fit over the air intake whenever I try again ...