There is no vacuum in a diesel intake manifold, that why there is a vacuum pump. You have to have a throttle to create vacuum.

The OM615 is a bit of an oddity it does have a throttle valve controlling air going into the engine much like a petrol engine.



It certainly uses negative pressure in the intake manifold to control the "pig's bladder" (as it is often called on this forum) as part of the injection pump regulator / regulation. If this diaphragm breaks the tell tale sign is an engine that revs too high (but not run away).


I'm not sure what else is tapped off the intake manifold - best to find a workshop manual (which isn't likely to be easy unless you're prepared to pay Mercedes a lot of dosh)

This is all correct. On my OM615, you can seen the gas pedal linkage connecting to the throttle valve (circled in red), with the vacuum line connecting to the fuel pump.

https://i.imgur.com/Nw1hiFl.jpg


What's nice about this is that I can still shut the engine off even if the vacuum pump fails. It does make the gas pedal linkage much more complicated, though.

So sorry for my prior statement. I used to be on some sort of forum for my 65 Lincoln and it really pissed me off when people who didn't have a 65 Lincoln but who had worked on "a lot of Fords" would chime in with their rubbish advice that applied to a Ford, but not a Lincoln. And now I've done the same. Well, to make this an educational opportunity, does anyone know the reason? Generating vacuum seems out because it has a vacuum pump. Seems to me it would need to be arranged so it would get air and fuel at roughly the same rate, or does it literally just open all the way as soon as you step on the pedal and is only there to allow for shutting down the engine by starving it for air?

Don't worry about it - the OM615 is a bit of a weird one (I think other earlier Mercedes diesels also had this weird arrangement - but I can't quote the numbers off the top of my head!)


I don't know for sure why this arrangement was used - I would hazard a guess (and it is only a guess) and say it is probably a Bosch thing. Or if it wasn't Bosch, perhaps the more commonly known configuration is more of a Bosch thing - dunno for sure.


If you want to "read all about it" the W123 FSM on the startek site for the non turbo OM61X engines has a big old write up in chapter 7 describing how the OM615 throttle valve system works. It then goes on to describe how the OM616/7 system works. Great anorak stuff (!)

Maybe I'm dense, but I can't find this section on the startek site! I see all the other sections in the engine manual, but chapter 7 looks like its only 'testing and adjusting jobs' and 'assembly jobs' -- but no write ups of how the systems work.

It isn't the easiest information to access with out a flash player that they happen to be using at the moment...


...so I've added direct links to the PDFs on startek for the non turbo chapter seven to this thread =>


http://www.peachparts.com/shopforum/3920886-post74.html

Thanks Stretch! I've also found the FSM for the W114/W115 models -- of which the 220D shares the same engine as my van, with a few small differences: Some Good Reading

Still waiting on clutch parts and engine mounts, but in the meantime I've reinstalled the vacuum pump, water pump, and thermostat housing with new gaskets. I also flushed out and de-scaled the engine and radiator. It really needed it!

After pulling off the intake and exhaust manifolds, I noticed that there's not one, but two butterfly valves on the intake. One is actuated by the gas pedal linkage, and the other seems to just rotate freely. It looks like the second one would be good for shutting off the engine in an emergency, but there's no way to close it unless you take off the engine cover and reach in to do it by hand. I'll have to do some more research on this.

I spent this afternoon laying underneath the engine bay cutting out the old transmission mount -- the metal sleeves of the bushings had seized to the bolt.

The second flap is devised to be free (not attached to anything), see:

http://www.peachparts.com/shopforum/450221-post10.html
http://www.peachparts.com/shopforum/diesel-discussion/71958-can-right.html

Added in the early 60ies and some documents describing the operation of pneumatically governed IP pumps show only one flap in the intake(like here):
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Engine/615/07-010.pdf

Thanks for the information! Anybody have a part number for the gasket between the butterfly valve assembly and intake manifold? And any general maintenance you'd recommend while it's disconnected?

A6360740280

I'd check for excessive wear on the shaft and lubricate from time to time...

new parts!
 

Finally got my new (well, NOS and used) parts in the mail from Germany, and starting buttoning the engine and transmission back up to reinstall. I've read the clutch alignment tool from a 90s S10 fits the 240d, so I'll try that out. Then with the new engine and transmission mounts I received, it should be a little easier putting the engine back in than it was taking it out with the seized transmission mount.

I also need to reline the rear brake shoes. I'll probably try giving this a go at home first, and then call around some truck/RV shops if I can't figure it out.

Excited to hear it run again!

Got the engine back in a a couple of hours one afternoon last week. It's been taking longer reconnecting everything! Lots of crawling underneath the van, which I haven't had to do in a while, with the engine out and everything. I' hoping to start it up again in the next week or so. Been running around the shops for different small parts -- brake fitting adapters, hose to bypass the heater, and taps and dies to clean up threads. The threads on the steering tie rod are damaged -- hoping that it's easily fixed.

I've also noticed the crank pulley has a rust hole in it. I haven't been able to source a replacement yet. Should it be the same part on the 220D/240D? No AC so only one groove.

https://i.imgur.com/9nmxVpA.png

Yours appears to only have three bolts. I have always seen six bolts, even on the early 615 in my shed. Maybe one with six holes will still work, don't know for sure.

Buttoned everything up over the weekend -- primed the fuel filter, connected up the oil bath air cleaner, and new coolant hoses and clamps connecting up the radiator. After fixing an unexpected waterfall from the thermostat housing (make sure that O-ring is in the right spot, oops), I connected up the battery and finally tried cranking the engine. Nothing. All the lights turned on, what could be wrong? Well, I missed the battery ground cable bolted to the transmission. Tighten that down and it cranks! After bleeding the fuel out of the lines and replacing the old corroded ground cable with a new one, it started right up with a satisfying clatter: https://www.instagram.com/p/B2NsjzklqgX/

I'm going to run some diesel purge through it, adjust the valves again, and then try and even out the idle. I'm planning on checking the fuel pressure, compression, injection pump timing, and cleaning the injectors. Anything else?