SS,

I think the Vac-Retard is on the ported connection just inside the butterfly so it sees vac at idle and retard timing.

Then that goes away when the throttle opens a little. With the the timing jumps about 11 deg.

The front or outer connection is ported outside the butterfly and dose not see vac at idle.

I think this is what you told me in a PM.

Wait, you said the back side. In that case you should see a small timing retard. Did you have vacuum on that hose at idle?

I think that only the later us cars had the solenoids ('86-'89). I think that the earlier cars ('76 to '80) had the cut-off valve. When boost builds up the cut-off valve removes the pressure from the back of the distributor diaphram and dumps it to the air cleaner housing instead. This item is frequently removed.

SS,

What is your opinion of removing the cut-off valve (sounds like a check-valve)?

If there in nothing to stop equal boost pressure from filling both sides of the Pot's diaphragm, it would not be able to retard on boost.

That would not be a good thing.

If somone wants or needs to run without somthing on the Vac-retard side to impead flow, it would be safer to run without the Vac-Retard side from being hooked up at all and just reset the idle at the air bypass valve.

The little vacuum solenoid in the boost retard line only closes during the first minute after a cold start so vacuum retard is blocked and doesn't reach the vacuum retard pot, the timing advances a little because of that, and idle raises about 3-400rpms for that first minute after a cold start.

There is no elctrical or mechanical boost sensor anywhere on the car that closes it during boost and the only other thing in there that could do it is the throttle position switch in the full throttle position and it doesn't affect that vacuum solenoid either... thats real easy to test, just open the throttle all the way with the ignition on, motor hot, and check the wires going to it with a voltmeter.

If you think that vacuum solenoid closes during boost so no pressure reaches the vacuum retard side of the pot, what do you think is sensing boost and sending 12 volts to that solenoid to close it?

The left vacumm solenoid in the picture up the page activates the air pump diverter valves and it is an emission control. That one also has a broken off vacuum line fitting on the top side so it is NFG and is not doing anything.

so safe to disconect the 2 solenoid if we have no cats??
Thanks

I got rid of the one that controls all the air injection crap. I kept the other one so I would have the high idle at startup.

Eric

I think it is safe, if you remove the hose from the back side of the distributor diaphram also.

Here is how I have been told the solenoid works at full throttle: The control unit gets the full throttle position signal from the throttle position switch, AND it gets the speed threshold signal from the speed relay. That is why I think the "Fairman test" does not make it work. To test it, you have to be above a certain RPM (don't know what) AND at full throttle. I never tested it though, so I'm not sure on this one.

That would be cool if you are correct that the vacuum solenoid in the vacuum retard line has dual purposes. Havn't heard or seen any indication that it does though. I guess you could hook up two long wires to it's plug and run them into the car and hook them up to a little 12 volt bulb and see if it lights up under boost while at full throttle.

What speed relay are you referring too?

If you mean the left hand smaller relay under the drivers seat, that one is the rev limiter that shuts down the ignition abruptly at 7200rpm.
I don't think it's a dual purpose relay with 2 sets of points.

The other relay in between it and the K-jetronic ECU is the full throttle enrichment relay which is hooked up to the throttle position switch.
It removes the oxygen sensor signal from the lambda emission control circut and puts it into open loop mode and the frequency valve to a set pulse frequency (70% I think) which richens the fuel mixture a little at full throttle.

Maybe that relay also operates the vacuum solenoid in the vacuum retard line in relation to full throttle position also?
I don't know, yet.

I am glad we are talking about this as I am not 100% on this.

How can the dual connection-pot push against its internal return spring when there is boost filling both sides of the internal diaphragm. With equal pressure on each side of the diaphragm there would be not movement and thus no retard.

Running the car up in the driveway for a test is not going to work. Only on a dyno so there is boost on each side of the throttle butterfly.

To test this we just need a hand pump teed to each side of the pot so it pressurizes each side at the same time. If the distributor plate moves, the timing changes, or idle slows, it is able to retard with equal boost signals.

If not, there has to be a check valve, a solenoid, or something to block the signal on the back side of the can.

Go to post 99. There are two solenoids in the picture. One is probably for blocking the on idle vac-ret signal and the other much be for the air pump.

Also, look at that schematic. I shows the solenoid on the Vac-Retard side of the pot.

Anyone have a hand pump, at tee, and some tubing and willing to test the pot?

What is driving the solenoid during the start up for a higher rpm?

What is used to bump/maintain rpm when the A/C goes on?

If the solenoid is used to block the vac-ret side for boost-retard, all that is needed is a low pressure sensor some where that senses boost in the intake manifold section I would think. I would not think it would depend on the throttle switch.

Anyone have a wire digram and can run down the source of the Distributor?

"What is driving the solenoid during the start up for a higher rpm?"
The K-jetronic ECU under the driver seat.

"What is used to bump/maintain rpm when the A/C goes on?"
Nothing does on a 930.

Having said that I installed a vacuum solenoid with a 10mm inside diameter from a late seventies BMW that bypasses the throttle body and opens when the AC compressor comes on.
It actually raised the idle about 100 rpms when the AC came on so I put a small spray gun ball valve inline with it so I could adjust the AC on idle speed to perfectly match the idle speed with the AC off. Works perfect.

"If the solenoid is used to block the vac-ret side for boost-retard, all that is needed is a low pressure sensor some where that senses boost in the intake manifold section I would think"
If there was "low pressure sensor" on a 930 I would have found it by now and/or someone would have found it and mentioned it by now.
There is no electrical MAP sensor of any kind on a 930.

You may be on to something here.

The only time we need Vacuum-Retard is when at idle. Thus, it could be closed at all other times.

I think there is a switch at the Throttle for idle. Thus, any time off idle, the solenoid valve could be closed.

Better yet, maybe the solenoid is on/ open when energized!

This would be better in the event of failure. With failure in the closed position we still have boost retard and there would be a noticeable increase in idle.

Makes much more sense.

If there is a timer and logic for cold start it cold easily handle not being open above idle.

A note, the ported vac line can only supply vacuum at Idle anyway. Our issue is getting boost there.

We definitely do not want vac retard on cruse.

Vacuum retard while decelerating lowers nitrogen dioxide exhaust emissions and the EPA likes that.
Thats the other reason it exists along with vacuum advance on USA cars with distributors since somewhere during the mid to late seventies.

I tested the 2 vacuum lines today to try and make some sense of it all.
At idle cold the blue, line, to the inner pot originally showed no vacuum then after a few minutes showed 13-15 psi steady at idle. By 4000 rpm it was 0 psi.

The red line, from the temp switch, to the outer pot at idle showed 0 psi at idle and before 4000 rpm it was reading 15-17 psi.
At no time was there any positive pressure on either. I did this while checking timing and my inner pot is blown so was unable to see what effects it actually has on timing. Just my 2 cents..
Very good thread and at a very good time for me

Makes sense and as it should be.

The cold start kills the Vac-retard at first using the solenoid.

The port for the Vac-Advance is a small hole just inside the butterfly. At idle it sees vacuum. When the throttle opens the whole moves to outside the butterfly to where the turbo has built some pressure, even at idle.

This connection is just outside the throttle butterfly at idle and thus would not see vacuum.

I assume you mean you saw vacuum. As the butterfly opens a little this connection moves past the butterfly and the hole then is inside the intake manifold portion. Thus, at 4k rpm steady state you were at no load and were seeing vacuum from the motor as you should.

Under load the intake manifold would fill with boost and you would see positive pressure. You can not get boost in the intake manifold in the driveway.


What do you mean your inner pot is blown?

From all the above it sounds like you are performing correctly.

Quote "What do you mean your inner pot is blown?"
There has to be 2 pots, the outter will hold a vacuum. The innermost vacuum nipple will not hold vacuum. I just figured there were 2 separate pots. I removed dizzy, cleaned and lubed, advance is fine. The inner was just free air with no effect on dizzy. There was evidence of rusty (liquid) running out around vacuum nipple and throughout the whole vacuum line.
I am on hold purchasing a new vacuum assy. and watching this thread for maybe an alternative (MSD).

The double connection pot should only move in one direction. It pushes a rod in toward the dist. The connection on the out side dose so with boost. The connection on the inside dose so with vacuum.

Any movement the other direction should just be the effect of pushing the diaphragm back against its stop.

If the outside holds vacuum that part is intact. If the inside dose not it might mean there is a hole somewhere on that outside of the pot. Your evidence of rust on that side supports this.

Might try putting it in watter and pressurizing it with a hand pump. That air has to go some where. If it comes out the other connection it would be interesting. I would think it would come out from a hole at the nipple connection or around the outside but just guessing.

Interesting.

OK started thinking about this stuff, went out to the garage, and fiddled with the dizzy again. I found of course the outside boost retard port will retard the dizzy under pressure. the inside vac retard under pressure will not make the dizzy move at all. However I tried applying equal amount of pressure to both ports such as full boost, the dizzy would not move. Just as stated by 911ST. Soo, how am I getting boost pressure retard? The vac retard port (inside) must not be seeing boost pressure, or is vented. I think if it were I would have disconnected vacuum lines that popped under pressure. Or does that side of the TB not produce any significant pressure?

Eric

Eric,

You made my week!

Major, major point!

Thank you very much!

This confirms we do not see boost retard without the a proper functioning solenoid.

If one wants to run with out that solenoid, they need to leave the vac-retards side disconnected or configure a check valve of some type so it dose not cancel out the boost-retard function.

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