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6.9 engine vacuum progress

Started by s class, 25 October 2007, 02:54 PM

s class

Hi guys,

I have been puzzling through vacuum diagrams and studying my two cars.  There are some differences between the two, firstly due to some obviously wrong connections and secondly because there DOES seem to be some difference between the very early car and the late car. 

In each of the pictures below, on the left is the blue car ('76 euro) and on the right is the red car ('79 euro)


First up, the warm-up regulator.  Both are the same, with the lower chamber of the WUR getting vacuum from the throttle side of the aux air valve and the upper chamber getting vacuum from the inlet manifold side of the aux air valve - I assume this is correct. 






Now the vacuum advance. 
The red car (right pic) shows the advance side - red tube - going to the throttle body - more detail in the next pic.  THe retard side goes via the clear/violet tube to the switchover valve.  I assume this is correct.  Any other opinions?  The blue car is clearly wrong with the retard side disconnected, and the advance side going to the switchover valve. 






Now where the vac advance vacuum comes from :



The red car (right hand pic) has the red line for the vac advance coming off the throtle body at about the height of the butterfly.  Is this correct?  At 9 o clock and 3 o clock of this connection point you can see two blanked off vacuum points.

The blue car is again clearly wrong.  In the upper left pic, the red line intended for the vac advance is plumbed off the inlet manifold (wrong I think - any other opinions?), and it actually loops back under the inlet manifold (bottom left pic) and connects next to the throttle body where the red car gets its pickup.  IN other words its just a loop never going to the vac advance unit  :o

Where should the vac advance pickup come from?

In the bottom left pic near the red line is a clear line - this loops back to the switchover valve - ???




Now in the top left frame of the above pic is another clear line connected above the throttle, and exiting the picture at 12 o clock - this line goes to the back of the motor and connects to this device, whatever it is - see below(left pic for the blue car).  THis goody will be getting high vacuum at small throttle opening.  In the red car, this device (see right pic) is connected to the crank case breather - you can see the line near the breather port on the tappet cover.  Surely this has negligible vacuum?  Which arrangement is correct?






Last one - switchover valve.  In the red car (right pic) the centrally located port of the switchover valve goes to the vac retard.  The other side goes to the inlet manifold side of the aux air valve.  Are these two connection points correct?  Does it matter which port of the switchover valve is which?



Any help gratefully received.

Thanks, Ryan


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

WGB

I'll be in the shed with both my cars tomorrow and will se what I've got and maybe photograph some detail as well.

You're asking a lot of questions in a short space.

I have some USA Vacuum engine control diagrams in Chilton's Repair and tune-up guide 1974-84 which include all the seventies and 80's USA V8's.

I will look over them tonight and see if there is any common ground and can copy them if you wish

Bill

s class

Bill I do have thayt Chiltern's manual.  It shows only diagrams with all the emission control equipment, and I'm battling to reconcile that with the simplified euro arrangement.

Yes sorry for so many quesitons. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

koan

From what I can remember the red car is right or very close, the blue one is a bit of a mess.

There are vacuum diagrams here including a 6.9 (for US I assume), for the euro model just leave out the bits you don't have (not absolutely sure about that).

I have some diagrams but my scanner is down after a software upgrade - yet again)

There was a change to the vacuum connections on the warmup regulator but from what I can see red is correct.

koan
Boogity, Boogity, Boogity, Amen!

WGB

Great Site Koan,

There will be no air pump or EGR presumably on the Euro motor and the vacuum advance (red line) is connected to the vertical fitting on the mixture regulator assembly (This connection is taken by the Exhaust pressure transducer in this diagram)  with a direct connection to the advance side of the distributor vacuum control (no T-piece).

Bill

koan

Quote from: WGB on 26 October 2007, 02:09 AM

... and the vacuum advance (red line) is connected to the vertical fitting on the mixture regulator assembly (This connection is taken by the Exhaust pressure transducer in this diagram)  with a direct connection to the advance side of the distributor vacuum control (no T-piece)....


Not sure what  point "vertical fitting on the mixture regulator" refers to.

The advance should connect to a fitting on the side of the throttle body, such that it only gets vacuum when the throttle is cracked open.

koan
Boogity, Boogity, Boogity, Amen!

WGB

There are three lines on the 6.9 schematic. One is shown going vertically and two travel forward horizontally. One of the horizontal ones is connected via a T connector to the vacuum advance. As far as I know, only one of these is used on a Euro and that is connected directly to the vacuum advance.

As the connector on the mixture regulator (throttle body) is nearly vertical I had assumed this was the one that is vertical on the schematic but on a second look the diagram is not clear how these 3 pipes actually connect to the Mixture regulator (Throttle body).

Bill

koan


On the K-Jet bit of the picture there are 5 pipes, the fat one going in at the bottom is the EGR exhaust gas going back into the engine. The next one up is all-the-time manifold vacuum used for various things.

The vertical one at the top is an atmospheric vent (not vacuum) for the EGR transducer.

The two sideways ones are the vacuum advance and the charcoal canister "suck" lines, both of which are uncovered as the throttle plate opens. Actually within the throttle body are three holes, first one uncovered is the vacuum advance and the other two in a vertical line above the first provide increasing degrees of suck for the charcoal canister.

The actual connections to the two sideways ports are vertical and on the side of the throttle body. The rear one is vacuum advance, the front (possibly larger) connection is for the charcoal canister (the diagram suggests the charcoal canister port is the first port uncovered, I don't think that's correct).

Not shown on the diagram are the and the fuel damper and the coasting bypass valve connections. The fuel damper is at the back of the engine, a small horizontal cylinder with a large fuel line on one end and a nylon vent line on the other which goes to the breather hose under the air cleaner box.

The coasting bypass valve is the round flat thing at the back of the engine with two large air lines and a vacuum line which is connected to all-the-time vacuum. One of the two large air lines connects to the manifold the other to the mixture controller at the back.

I'll try to get my scanner going and scan the AUS 6.9 diagram, description and testing which maybe of use to you.

koan
Boogity, Boogity, Boogity, Amen!

s class

koan,

Thank you so much for that description - its the clearest and most logical description I've yet seen.

The only part I'm hazy on now is this item :



In the left frame (blue car) its the canister located diagonally in the centre of the frame.  Is this the fuel damper or the coasting bypass valve?  On the blue car the vac line from this canister goes to 'all the time vacuum', while on the read car it goes to the crank case breather.  The blue car does not have provision for such an arrangement - the crank case breather lacks the port that the red car's breather has for a vac line.

thanks


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

koan

Quote from: s class on 26 October 2007, 12:37 PM

In the left frame (blue car) its the canister located diagonally in the centre of the frame.  Is this the fuel damper or the coasting bypass valve?


That's the fuel damper, there is no coasting bypass valve on either car.

If the diaphragm in the damper leaks the vent carries the fuel away rather than letting it fall on the engine.

I would connect it to the atmospheric vent on the top of the K-Jet housing if there is provision, I don't like the connection to all-the-time vacuum, probably OK functionally but not sure.

A new breather hose would have the hole, or actually it would have the piece for the hose moulded in but blocked needing to be drilled out.

koan
Boogity, Boogity, Boogity, Amen!

s class

koan thanks a million.


Why do I not have a coasting bypass - would that be associated with Aus or US spec cars?

You talk of connecting it to the atmospheric vent on the k-jet housing - meaning the air filter box?


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

koan

Quote from: s class on 26 October 2007, 01:09 PM

Why do I not have a coasting bypass - would that be associated with Aus or US spec cars?


It is an emission reducing thing as well as serving to increase engine revs immediately after starting for a few seconds so maybe your market didn't get them.

Quote

You talk of connecting it to the atmospheric vent on the k-jet housing - meaning the air filter box?


I meant the vertical point I called the atmospheric vent, directly above the throttle plate which connects to the EGR control valve - which you don't have?

koan
Boogity, Boogity, Boogity, Amen!

s class

No I don't have EGR's.  Its now 9pm here and raining.  I'll go and have a better look tomorrow to see if I can locate this port 'above the throttle plate'.  I guess that point would not differ too much from the engine breather point.


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

Mercmad

Ryan,see you at m-100.cc for a clear explanation. The damper is not normally connected to vacuum but to the right hand cam cover vent contour hose. it's just fitted to lessen pump shock and noise while driving. Some have a vacuum connection some don't.