Mystery electric solenoid valves/vacuum lines

[mark houghton]

Riddle me this: I didn't have these gizzmos on my first 930 and now that I have the top of the engine exposed, thought I would check everything out.

The valve on the right has the top hose going to the back side of the dizzy vacuum can, and the bottom hose to the throttle body. I 'think' it's supposed to block ignition retard at startup to advance timing and set a high idle....until something(?) tells it to do otherwise once warmed up or timed out. I pulled the hose off the dizzy and can blow through it and hear the air going into the TB, so the valve is open stone cold.

The other valve on the left has nothing connected to it but a short piece of vacuum line going nowhere and no electrical connection.. May have something to do with air injection control to the exhaust manifold but just guessing as both of the injection manifolds have their own dedicated vacuum operated valves linked to the TB. Somewhere I'm sure I have a diagram of all the vacuum lines etc but thought I would reach out here first.

Almost got her all buttoned up following the fun and games of adjusting the valves.

[porschyard]

You are correct the solenoid on the right blocks the vacuum retard on cold start for idle speed increase and the one on left is for the air injection changeover from exhaust port to cat converter.

Richard

[mark houghton]

Originally Posted by porschyard

You are correct the solenoid on the right blocks the vacuum retard on cold start for idle speed increase and the one on left is for the air injection changeover from exhaust port to cat converter.

Richard

Thanks for confirming. That valve is supposed to be thermo timed, so I'm presuming it's wired in to the thermotime switch cold start injector circuit to get its timed power.
Just now bench tested the solenoid. The valve closes when 12vdc is applied to it. So in order for it to advance timing at startup, it needs to close when it sees power and open back up a few seconds later. Guess I'll have to pour over the electrical schematic diagrams to see where it gets its power...if it's getting any power at all that is and may just be permanently open if not. My car ordinarily fires right up and idles at around 1000 initially, mostly due to the AAR action. Not a big issue either way.
No cat on this car, so the other valve is of no consequence but thanks for telling me.

[mark houghton]

For any curious minds watching this thread, I'm not getting any power to the plug for that "retarded" solenoid. Poured over the electrical schematics and it appears to get its power through terminal 7 on the fuel enrichment control unit, so perhaps some timed circuit exists there. NOTE: When I checked for voltage I pulled the airflow sensor charging pressure relay (infamous yellow relay) because I didn't want the pumps running. May check for voltage again once I have the car up and running.
So it really begs the question: Why do we want the timing at idle to be retarded in the first place, other than setting a baseline timing? I think it's emissions related, retarded timing tends to create higher exhaust gas temps, thus keeping the catalytic converter nice an hot. Other than that there's no value in retard at idle since it will all go away once you open the throttle and vacuum advance kicks in. These dual pot distributors were just an emissions thing if I'm correct. I'm tempted to remove that valve altogether.
Thoughts?

[908/930]

I'm quite sure you are correct about why the timing is being pulled back at startup, helps to get the cat up to temp quick.

[Jeff NJ]

I can't tell you exactly what I did with hose routing, but I did remove those solenoids when I cleaned everything up and had the engine out about 10yrs ago and I never looked back. Someone here told me they were emissions related and I have no cat either, so it was a no brainer for me.

[mark houghton]

100% emmision related, the only purpose to heat up your cat when you're idling along in traffic. Just shunt vacuum lines around the solenoids.
I'm just trying to figure out how they're energized, not that it really matters but inquiring minds want to know.

[billjam]

If you are trying to track plumbing on an emissions-equipped 930, this diagram might help.
It comes from the back of the 930 Owner's Manual if I recall.

[mark houghton]

Originally Posted by billjam

If you are trying to track plumbing on an emissions-equipped 930, this diagram might help.
It comes from the back of the 930 Owner's Manual if I recall.

Yep, I've got that and it is helpful. Specifically what I'm trying to decipher is electrical, the power/signal source for solenoid valves 37...one for startup vacuum retard blocking and the other sends a vacuum signal to air switching valve 33 for the air injection operation.
Terminal 7 on the fuel enrichment control unit (under the drivers seat?) seems to be the power source for both solenoids...but what tells them when to activate? The shop manual says the "thermo time valve" (to the dizzy) is closed at cold start to block retard and thus provide 15°advance, and opens back up in 20 seconds. Must be some sort of bimetalic strip inside the solenoid that heats up and and opens the circuit.

[Speedy Squirrel]

They solenoids are supposed to be connected to each other as shown below. They share the same ground and control input.

[pkabush]

I can't tell you exactly what I did with hose routing, but I did remove those solenoids when I cleaned everything up and had the engine out about 10yrs ago and I never looked back. Someone here told me they were emissions related and I have no cat either, so it was a no brainer for me.
__________________
1988 930 Venetian Blue

Highly recommended ^
If you delete all that stuff and put on a aftermarket air cleaner it makes it so much easier to work on

[mark houghton]

Originally Posted by Speedy Squirrel

They solenoids are supposed to be connected to each other as shown below. They share the same ground and control input

Yep. The diagram I have shows terminal #7 on the enrichment control unit, for a 1986 model (mine's 1987), vs #12 on your diagram. Different years?

Now twist your brain around my logic:

Either way, no power getting to them. When bench tested, the solenoids open up with 12vdc. According to the shop manual for 1978 and beyond, they're closed when cold (i.e., no power) at initial startup...which would prevent the vacuum signal going to the retard port on the dizzy and give you 15° of advance for high idle. Then supposedly 15-20 seconds later they magically get 12vdc, open up, and vacuum retard kicks back in to 1° ATDC. I could investigate the enrichment control unit (something to do with the Lambda I guess but not sure it's function). Perhaps...perhaps, because I have my O2 sensor unplugged and running open loop its freaking out the unit and not delivering power to the solenoids.

So in the absence of idle vacuum retard due to an inactive/closed solenoid, timing should advance to 15° BTDC...vs the spec of 1°ATDC with hose connected...just as if you were to pull the hose off the dizzy you would see 15° BTDC.

Bottom line, I tune to 12-15° BTDC at idle and runs perfect. May freak some people out "that's too much timing"!! but that advance would happen anyway once you open the throttle and the vacuum port in the TB loses its vacuum. We don't really need that dual port dizzy vacuum can in my mind, just emissions crap to for retard when idling along to keep your cat hot.

My view on things, could be wrong, always open to learned wisdom from others.

[Speedy Squirrel]

"The diagram I have shows terminal #7 on the enrichment control unit, for a 1986 model (mine's 1987), vs #12 on your diagram. Different years?"

Yes, you are correct. There are two different Fuel enrichment control units, 930 617 131 01 and 930 617 131 02. They both do the same thing, but have different pinouts. The newer one has more pins, but they are not used for the 930.

[Speedy Squirrel]

Here is the description of the vacuum connections on the '86 to '89 930 throttle body. One of the big differences is that the cold start idle is now controlled entirely by the idle air bypass valve. There is no vacuum from port V to the front side of the distributor until the throttle is opened slightly.

[Speedy Squirrel]

Here are the results of my tests on the 1986 to 1989 930 distributor, P/N 0 237 302 045 with PGFU6 ignition control capsule.

For vacuum applied to the front and not the back advance occurs
For vacuum applied to the front and the back advance occurs
For vacuum applied to the back and not the front no advance occurs

Here are pictures of my tests with 1 bar pressure:

[mark houghton]

Originally Posted by Speedy Squirrel

Here is the description of the vacuum connections on the '86 to '89 930 throttle body. One of the big differences is that the cold start idle is now controlled entirely by the idle air bypass valve. There is no vacuum from port V to the front side of the distributor until the throttle is opened slightly.

Speedy: Absolutely priceless info and description. You probably posted this eons ago, good to bring it back to the surface. Thanks.
Will be printing this out and adding to my pile of stuff so I don't ask the same question 10 years from now.

[mark houghton]

Originally Posted by Speedy Squirrel

Here is the description of the vacuum connections on the '86 to '89 930 throttle body. One of the big differences is that the cold start idle is now controlled entirely by the idle air bypass valve. There is no vacuum from port V to the front side of the distributor until the throttle is opened slightly.

For the sake of clairity, when you say "front" of the dizzy, do you mean the side that cant be seen facing toward the front of the car? To me, that's the back of the dizzy. Very important distinction to be on the same page.

My hoses might very well be installed reversed...not color coded, all black... and I'm pretty certain the V port on the TB goes to that thermo valve way back by the breather and on to the "back" of the dizzy, not the front. Should have done a better job mapping it out when I had everything off the top of the motor.

If the front (nearest hose facing me) actually does advance, perhaps I should shunt around that solenoid going to the front of the dizzy, since it's permanently closed (no power going to it), and thus gain vacuum advance from part-to-1/3 throttle.