Vacuum/ run-over issue

[brokentroy]

Hi all,

I've been having issues with vacuum and and run-over for the past few months on my 1980 300SD.  I've replaced nearly every vacuum connection I can find.  there were many that were loose so I replaced them.  However, I still have not resolved the issue. 

Today, I was doing some work on the turbo when I discovered that the hose that comes off the top of the valve cover, next to the oil filler, was cracked.  Not sure what this hose is called.  Is it the blow-by?  Anyway, it goes from the cover to the turbo.  I drove the car to the auto parts store to find something to replace it with and when i got there the run-over was worse than ever.  when I turned off the ignition and pulled the key it was as if I had done nothing.  This was not normal.  Normally for me the car would spit and sputter for a few seconds, maybe longer, and then shut off.  But not this time.  So, I opened the hood to use the stop lever, and out of curiosity, put my hand over the remaining bit of hose that leads to the top of the valve cover.  The car shut off instantly.  I turned it back on and created the same situation.  Except, this time I put my hand over the bit of hose that leads to the turbo.  no change.  I put my hand over the other part again and it shut off immediately. 

I bought some parts at the store and created a makeshift connector for the hose.  I tightened all of the ends to get a good seal.  However, the car still will not shut off.  If I remove the hose and cover it with my hand again it will shut off. 

I guess my question is, what is this hose exactly and could there possibly be some sort of leak on the turbo end that is allowing air into the vacuum system?  or could there be something else going on entirely. 

thanks for any help. 

[brokentroy]

i just looked in the manual and the hose is called a Crankcase ventilation pipe. 

what is the function of this in relation to vacuum?

thanks

Troy

[WGB]

Presumably the crankcase is kept at a slight vacuum to make sure all noxious vapours are consumed by the engine but that shouldn't affect your vacuum supply to your ancillary systems.

- Doesn't the turbo-diesel have a vacuum pump ?on the back of the alternator? - this would need to be checked.
- If a non-return valve near the fusebox has a fault a leak anywhere in any of the systems will affect the whole system.

Bill

[brokentroy]

Thanks. 

I did check the vacuum pump at one point and it seemed ok.  I'll try it again.  Not sure what a non-return valve is.  is that the same as a check valve?  If so, I've replaced one near the fuse box.  I'll try the other one too. 

What's strange is that when I bought this car in April the vacuum system was fine.  Then I made the mistake of repairing the main vaccum line off the pump because it had a crack in it and was being held together with electrical tape.  I put a shunt in it and epoxied it together.  I checked it for flow before putting it back on and it seemed ok.   But now I have issues with the vacuum.  Door locks only work when the car is running.  brakes are sometimes hard.  (I've checked the booster.  it holds vacuum).  And then there's the run-over issue. 

If the problem is with the pump, then why would the car turn off right away when I block off the crankcase vent?  Wouldn't there still be a leak?

I'd really like to resolve this myself, but if I can't figure it out soon, I'm going to have to have a mechanic look at it.  Only because this is also affecting my climate controller and I'm going to need my defroster real soon. 

thanks again. 

Troy

[WGB]

I have never worked on that model of Turb-Diesel as they are US specific and nobody else in the world had them.

The workshop manual in the library has some very good test procedures for the vacuum system and I would sytematically work through them using the colour codes for the year of your car.

Yes the check valves are what I was talking about when I referred to a non-return valve.

You obviously have a snafu pump or a major leak and I would think you would need to purchase a small vacuum test pump and work through the system one part at a time until you find it.

The money spent on a cheap vacuum pump (Probably $50 to $100) will be nothing like the cost of getting someone who may know even less than you to "experiment".

Bill

[Big_Richard]

if your having issues with the engine still running after turning the key off, this is a very common issue which I've seen rased on other forums quite often.

Have a read of this document in relaition to testing the vacuum shurt off system on the injection pump for leak tests. http://handbook.w116.org/Engine/617/07_1-150.pdf

[brokentroy]

thanks.  I'll check this out. 

i did discover the other day that I have a leak in the pump.  with the engine off I disconnected the a line on the booster line nearest the pump and blew into it.  i could hear air escaping form the pump.  I think I will get a repair kit and try to fix this before troubleshooting further.

Troy

[Sev]

Presumably the crankcase is kept at a slight vacuum to make sure all noxious vapours are consumed by the engine but that shouldn't affect your vacuum supply to your ancillary systems.

- Doesn't the turbo-diesel have a vacuum pump ?on the back of the alternator? - this would need to be checked.
- If a non-return valve near the fusebox has a fault a leak anywhere in any of the systems will affect the whole system.

Bill

yes it does not affect the vacuum to the rest of the system.

yes, TD's (i.e. 300sd's, both w126 and w116) do have a diesel vacuum pump. some of them have two tubes sticking out of it, one of them going to the air cleaner box.

i have no clue what a 'non-return valve' is near the fusebox--care to show me the diagram in the online manual?

[brokentroy]

Thanks.  I don't think the problem is my Vac pump.  I put a mightyvac on it and it held vacuum.  did the same on the brake booster with the same result.  I tested the line that goes to the accumulator and was not able to hold vac.  I disconnected the line and plugged it up.  now the car shuts off right away.  I do have locks and stuff right away, but after a few sec no more locks.  as long as the car shuts off that is all I am concerned about right now.  I am going to replace the accumulator as soon as I get a chance.  Hopefully that will resolve the issue. 

Troy