Holy crap!

7 seconds to bog down...

Hmmm I'll give it some thought.

As for the crankcase pressure effecting the vacuum pump.

Assuming you've got a piston pump => I can imagine that it would be harder for the pump to push against the crankcase pressure. If the non return valve in the vacuum pump was leaking then I can imagine that the piston assembly would be pushed back towards the engine so that the bearing race is always in contact with the bearing track on the front of the timing device. I think the crankcase pressure would reinforce the spring pressure in the piston vacuum pump.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

The shuttoff issue does not have to do with the Vacuum Pump.
It has to do with the fact that the Fuel Injection Pumps Camshaft and Governor Housing are connected to the Crankcase and exposed to the Crankcase Pressure.
One side of the Vacuum Shutoff Diaphragm is esposed to the Crankcase Pressure that is in the Fuel Injection Pump Governor Housing.
If the pressure inside of the Housing rises enough it pushes the Diaphragm the same direction Vacuum would pull it if you applied Vacuum to it and can shutdown the Engine.

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84 300D, 82 Volvo 244Gl Diesel

Oh right - sorry I misunderstood what you meant.

Very interesting problem for the Mercedes Myth Busters here. I like it! The more we talk about these cars the better we get to understand them - we get to a stage where we think we've seen it all before and wham bam! here comes another little idiosyncrasy.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Technically the suction through the existing leak of the rear seal should reduce or eliminate it to an unknown degree. This would mean a continious vacuum state in the engine would have to be sustained..

How much of a pump might be required in capacity to achive this really an unknown and could be variable or substantial as well. Depends on how much deficiency is present with the present rear main seal as well.

You will probably have to incorporate a good oil seperator as well.

As tough as it is I would change the seal instead. All the fumes produced would have to be carried to the rear of the car I suspect to avoid making passengers sick is another concern. I was even thinking of a venturi effect but not practical at low speeds.

I've been reading though the FSM trying to find out more about the return flow of oil from the IP.

Chapter 18-005 in both the turbo and non-turbo FSM versions don't help much. The only mention I can find about the return is in chapter 7-010 showing the "new" oil fed injection pumps...

...Oil goes in via the intermediate shaft and returns "to the crankcase" - how it gets there and the path it takes isn't clear in the FSM. I'm going to have to take my engine to bits again to see!


Even so for the crank case pressure to effect the diaphragm at the end of the IP the crank case pressure would have to be greater than the oil pump pressure...

...wouldn't that cause lots of other lubrication problems within the engine? Jets on the turbo OM617 version would have trouble spraying oil up and into the bottom of the cylinders for example.

Now I don't know by how much the oil pump pressure gets reduced by the time it reaches the IP (and crawls its way though the small path way through the intermediate shaft) - I guess that needs to be measured - but how?

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

After the Oil goes into the Fuel Injection Pump Housing it fills the Pump up to the level of the slot in front of the Pump and the excess Oil Drains out (instead of slots I have see pics where there is 2 holes that do the same thing).
So there is always a captive amount of Oil inside of the Fuel Injection Pump Housing once it has been filled.

Once the Oil Flows into the Pump Housing there is no Oil Pressure. The Oil just lays in the Sump like the Oil does in the Oil Pan.
The Fuel Injection Pump Camshaft is Under the Oil Level and the Bearings are almost completely immersed in Oil.
When the IP is moving plenty of Oil gets splashed around to lubricate the parts above the Oil Level.

Remember the Older Fuel Injection Pumps have no lubrication from the Engine Oil; you have to fill the IP with Oil and keep an eye on the Oil Level and for Fuel contamination.

I think everybodys questions but mine are getting answered in this thread!

See the green circle and arrow in the pic to view the drain slot from the pic I barrowed from another thread.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

That must be some pretty severe blow by if you need to pull vacuum on the CC to bring to tolerable levels.

I had excessive CC psi for a long time, it got worse ever since i installed a 'cold' (use the term loosely)air intake. I vented CC to intake pipe thinking the vacuum would assist with venting. Not so, and as a result I chased oil leaks for a couple of years, did all the hard jobs with engine in car and the leaks kept coming. Finally i vented to atmosphere and the leaks all stopped. Why it took me two years and countless hours of seal/gasket changes to finally try this? no good answer, and in hind sight seems pretty dumb.

If you have not tried to run open to atmosphere do try this first. I used a catch can which dumped to oil drain pipe, CC was vented with 3/4 hose right out into Pass side coil spring. The spring is an oily mess now but who cares..

Gone are the days of an oily/dirty rear hatch, and big oil spots on inlaws driveway!

I am in the process of installing another engine now, i am confident this one is much healthier then the one i removed. I had bad blow by when i bought it 7 yrs/150k miles ago, now has like 350K on it. HG blew or head cracked which is why i finally swapped it.

I'm surprised to read that.

My experience (which is most definitely less than yours!) is that the oil shoots through the intermediate shaft with some impressive force. I found this out the hard way whilst arsing about (playing) with my engine with the IP off. I cranked by hand and then wondered where all the oil was coming from - there was shed loads of it all over the place and I'd only turned the crank about three times.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!