Vacuum Thermovalve?

Unfortunately, I'm STILL trying to solve a CIS issue with my '78 SC. Basically, it starts, idles fine at 1,400 RPM for about 60 seconds, then starts struggling and nearly stalling.

I've removed the heater components, and now have a straight shot at the Vacuum Thermovalve. I pulled the vacuum hose going from the Thermovalve to the WUR, and when putting my finger on the valve nipple, noticed a slight bit of suction present. This is with the car having sat for around 7 hours in cool weather. I have been advised that when cold, the Thermovalve should be closed, so does the slight bit of suction indicate this may be bad?

Another thing I did was blow on the hose going into the WUR, and noticed the engine began to run rough. I sure hope I didn't damage the WUR by blowing into the vacuum hose! I know what you're thinking, but I used mouthwash prior to this activity. 8)

It was also mentioned that the Auxiliary Air Regulator may be deactivating too quickly, before the WUR is activated, and that the initial fast idle is too slow. Will tapping in the metal plug serve to raise the initial idle speed and duration of the fast idle?

Could the Thermo-time switch be at fault?

I've scoured the web for CIS information, and have printed several good articles. Cold start problems seem to be blamed on the "cold start valve and its circuit," or the Auxiliary Air Regulator.

I'm sorry to burden everyone with this, but I simply can't afford another $65/hour troubleshooting session. When I finally get this squared away, at least I'll be qualified as a CIS contributor on this BBS!!

While your car is struggling and nearly stalling, can you just slightly lift the CIS sensor plate and get it to idle smooth? This will tell you if you're getting too lean a mix during cold start.

If you are too lean, you can disconnect both vacuum lines to the WUR and see if your problem improves. That will cause the WUR to be in full throttle enrichment all the time.

Don't blow your WUR again. It won't hurt it, but there's probably some kind of law against it.



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Bill Krause
'79 911SC Euro

Ok, thanks to your help, I think I may be making some progress!! I started the car from stone cold this morning, and this is the result:

1. First key turn, ran for 1-2 seconds, then stalled.
2. Second key turn, struggled for a second or two, then settled into its typical 1,400rpm idle.
3. Idled at 1,400rpm for 30-45 seconds, and then started running extremely rough, nearly stalling, at which time I lifted the sensor plate slightly, and the motor straightened out. Letting the sensor plate return to its original position caused the motor to run very rough and nearly stall again.
4. I could only find one vacuum hose connected to the WUR, originating from the small thermovalve. I disconnected the vacuum hose from the WUR, and the engines rough running was not affected at all.

Now, a couple of questions please:

1. Does this indicate a defective WUR?
2. During the struggling process, there is a heavy fuel odor coming from the exhaust, along with puffs of whitish smoke. It seems counter-intuitive to me that the motor would be running lean. You would think that a rich running motor would smell of fuel, so how does a lean running condition cause the heavy fuel odor?

Thanks very much for you thoughtful insight!!!

Are you sure you don't have two vacuum lines? One will be at the bottom and comes our of the WUR horizontally and goes to the thermovalve. The other should come out the top, and go to the throttle body.

This pic shows it. As you can sort of tell by that picture. The two vacuum lines come out of the throttle body, on either side of the throttle plate. The two vacuum lines work against each other to move a baffle inside the WUR. When the two vacuum lines have the same amount of vacuum (ie. wide open throttle), then you get a richer mixture. Disconnecting the bottom line from the WUR should cause this to happen also.

http://www.pelicanparts.com/911/911_Parts/1978-83/1-7-2.JPG


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Bill Krause
'79 911SC Euro


[This message has been edited by wckrause (edited 03-20-2001).]

Sea,

Just an idea, but what about the thermotime switch remaining grounded for too long and causing a rich condition by operating the cold start valve longer than it is supposed to. I think this valve should only operate for 3-10 seconds from the time you start cranking the starter. If it runs longer, it may cause too rich of a mixture as you think you may have. You can test the TT switch. It should measure 2000-3000 ohms at stone cold, and somthing like 25-50 (I think) at warm/hot.

Just a thought you may want to check!
Nick.

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_ _ __ _ _
Nick Shumaker
1982 911SC Coupe
nickshu@yahoo.com

The gas smell would make you think it is too rich, but lifting the sensor plate to get a smooth idle, shows it's too lean. Still it's worth ruling out.

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Bill Krause
'79 911SC Euro

OK, I've been heading straight out into the garage as we work with this thing, and I apologize, as there is a second vacuum line. It was obscured by the intake, and is a completely different type of hose that I mistakenly thought was routed to the distributor.

One thing to note is my vacuum hose routing is not the same as the diagram that was posted. The routing is as follows, using the diagram as a guide:

1. From the WUR, hose #16 goes to the thermovalve, not the throttle body, and there is no part #17 in-line. Also, the hose has a "T" with a vacuum line running to the distributor (vacuum advance I would assume).

2. From the WUR, hose #13C goes to the throttle body. I found the connection was not very tight at the throttle body end.

This morning, I ran the engine for no more than 3-4 minutes for the test, and then turned it off. I just went outside and started it again (it sat for 5 hours), and it started right up, and while it idled slightly rough and at a low rpm, it did not get into the stalling mode (now I'm really confounded). I proceeded as follows:

1. I removed both vacuum lines from the WUR, and it started to run terribly, almost stalling (very much like it does after being started from stone cold).
2. I re-attached both hoses, then removed only the line from the top of the WUR to the throttle body, and noticed no difference. Further, I didn't notice any vacuum on this line, or the nipple on the throttle body.
3. I then removed only the hose that runs from the WUR to the thermovalve, and the car ran terribly again.

I'm afraid to ask, but are we getting any closer? Could the hose routing be causing the problem? Any idea why it didn't go into the stalling routine after sitting for several hours? It seems to do it only when started from stone cold.

Thanks again everyone! I never dreamed it would get this involved.

That is an interesting theory. In practice, the Cold Start Injector/Valve should inject gas into the intakes for no more than 8 seconds (max.) via the thermo-tine switch. If the switch had a mind of its own, it would be just as happy to keep injecting straight gas into the intakes regardless of anything else.

PLEASE CHECK MY MATH HERE!:
Just so I understand, when we start our SCs ('78 SC for me) from cold, the Cold Start Injector sprays gas at a rate of 0 seconds (90degrees or above) to 8 seconds (-4degrees or less) into the intakes. Also, as we crank the engine, the Auxilary Air Valve is providing a "clean and reliable" air source for the starting sequence; its effect is ended as soon as the engine starts and the AAV is shut down by way of true vacuum from the now-running engine (counter-vacuum: folks who have "hunting"idles should check this closely as the diaphragm may be jumping back and forth).

Meanwhile, other devices that are time- and temp-related are in effect: the WUR has current applied to it, and it begins to move from a state of bleeding pressure from above the control plunger in the CIS unit to richen the mixture, to a state of having no effect anymore: this by way of bimetallic arm that is eventually defeated by a spring that pushes a plunger closed.

At the same time, our Auxilary Air Regulator is beginning the task of turning its disk from an open position to a closed position, and thereby slowly preventing extra air from entering an orifice below the throttle plate (i.e. the butterfly). This air lets the engine run at a higher idle, and is slowly turned down by the rotation of the disk.

So what is happening with your SC? You start it, it seems to catch, then die: from flooding? Finally catches, runs at 1400rpm because the air/gas mix is (reasonably) OK. Then, you are starting to lose extra air under the throttle valve (butterfly) as the AAR moves out of the picture, and now you have a rich mixture that is causing your car to stumble. Where is this rich mixture effect coming from? The WUR is the thing that is keeping your car rich by way of venting pressure from above the control plunger of the CIS, so is that the culprit? Or is the thermo-tine switch continuing to allow the CSInjector to pump straight gas into the intakes?

I know the AAR and WUR overlap, so I wonder if the AAR is leaving the scene too early, and leaving the WUR in full effect or thereabouts, causing a rich mixture and causing the car to stumble. Lifting the sensor plate seems to confirm that leaning out the mix is curing things, but I am unsure if, by lifting the sensor plate, you are actually leaning the mixture...I just don't know enough.

In all events, I guess I'd pull the hose from the back of the intake throttle (butterfly) and see if things improve. I *think* what I am recommending here is a test to lean the mixture with extra air at that orifice.

I am very interested in what anyone else has to say on this subject. I am actually writing up a piece on how the early SCs (78/9) start from cold. I won't get into the condition on my car---it starts and throttles down to idle nicely, but does like to float the idle, when warm, at around 1800rpm. I can defeat this by "deading" the engine via a brake on/clutch out method that slows the idle down. But this is SeaDweller's post so I am leaving my problems for another post. I will say that, in frustration, I did a douse of carb cleaner fogged into the AAR from the receiving end and the car now comes to idle (900rpm) very quickly at a stop.

I will investigate more tonight in the Bentley book. Sure wish it simply descirbed the warmup sequence for our cars...but maybe that's too much to ask considering the amount of information on this board about this.

Done rambling,
Jw

Jdub- I follow you, but I think SeaDwellers engine is running too lean on cold start. That's why when he lifts the CIS Sensor plate (by hand) it straightens out the idle.
Lifting the sensor plate enrichens the mixture, it doesn't lean it.

SeaDweller -- I think your vacuum lines are swapped around. I'll check my hoses tonight and get back to you. There is also a diagram in the Haynes manual that I'll check too.

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Bill Krause
'79 911SC Euro

Jdub-- You mentioned that after warming up, the WUR no longer does anything. This is incorrect. It continues to regulate control pressure, and performs both altitude compensation, and full throttle enrichment (at least on the 78-79 models).



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Bill Krause
'79 911SC Euro

Ah, thanks! And yes, I was unable to follow why the hoses on SD's WUR were routed as they seem to be. I think you might have something there.

Jw

***********UPDATE***********

I wanted to make sure I'm communicating accurate information, so I took the vacuum hose diagram and compared it against my car. One thing I don't see on the diagram is a line to a vacuum advance on the distributor, which my car has. I wonder if it's possible that my vacuum hose routing is different than the diagram because I have the vacuum advance distributor?

Anyway, if the diagram is accurate in it's depiction of the parts, such as location of connections, etc., this is how my car differs from the diagram (I've already mentioned #1 and #2, but I'm listing it again to keep myself straight):

**Please note that there are 2 lines numbered 13B, so I have listed the number sequence to identify the proper line.

1. From the WUR, line 16-17-13B goes to the center nipple on the thermovalve (instead of the throttle body, and not the offset nipple on the thermovalve), and there is no part #17 in-line. Also, the hose has a "T" with a vacuum line running to the distributor (vacuum advance I would assume).

2. From the WUR, hose #13C goes to a visible connection on the throttle body.

3. Line 13A-14-13B is going to the offset nipple on the thermovalve (as opposed to the center nipple shown in the diagram), and line 13 goes to a connection behind the throttle body (it is on the back side of the throttle body, not in proximity to the other connection as shown in the diagram).

Bill, I notice that you have a '79 Euro spec car. Do you have a vacuum advance on your distributor?

1. If the vacuum system is complete, despite some different hose routings, shouldn't the system still operate properly?

2. I wouldn't think it should matter which thermovalve connection is used, as it's just a valve that opens and closes a vacuum, so either connection would be identical, wouldn't it?

3. Is it possible that the 2 different connections on the throttle body draw a vacuum at different times, or is it like the thermovalve where both connections are under vacuum at all times, meaning both connections would work identically?

Once we get this figured out, Happy Hour is on me!!!!!!!!!

The connections on the thermovalve are interchangeable, but not the connections on the WUR, or the throttle body. Once the thermovalve is opened up, it may result in your vacuum lines actualy being connected correctly, but it may be pinching off the wrong vacuum line during cold start.

I have a vacuum advance on my distributor also. I'll verify where it is connected tonight when I get a chance to look at the car.

I'll get back to you later on tonight.

If it's any consolation, once I got the bugs out of my CIS system, it now starts easily at 15 below zero. No stumbling idle, and no backfire.



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Bill Krause
'79 911SC Euro

Thanks Bill!!!!

By the way, when you're peeking under the lid, let me know if you have the same throttle body as mine, that being with a vacuum line on the front (where the WUR is connected in the diagram), and in the back, where the vacuum line from the very top of part #7 in the diagram is connected. It would sure make things easier if they were both situated in front as idicated on the diagram!!

I can't begin to thank you for your help!!!!

Michael

Here is the vacuum diagram from the Haynes manual. It is for a '79 911SC. My vacuum connections are identicle to it.



I'll go check the throttle body, but I doubt if they are different.

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Bill Krause
'79 911SC Euro

I looked at my throttle body a little closer.
The line from the distributor, goes to the back of the throttle body, the line from the top of the WUR (16-17-13B) goes to the front of the throttle body near the top (like in the drawing). The bottom connection on the WUR goes to the thermovalve. From the other side of the thermovalve, I'm not sure where it goes. I can't see it unless I take a few things apart. It doesn't appear to go to the front of the throttle body. Maybe it's on the back near the bottom. I don't think there is any difference in connecting to either the front or back of the throttle body, but there is a difference in connecting to the top or bottom, because these connections are on different sides of the throttle plate, and will see different pressures.

It might be a good idea to verify my connections with someone who has a US version like yours, but I'm suspecting you've got a few things mixed up.

If your car starts, and then dies, on the first try, and after 2nd or 3rd time the car idles low then rises after its semi-warmed up, and the problem with starting only happens when the car is been sitting overnight or a long time, but is fine the rest of the day, then you need a new warmup regulator.

rfng:

As you wrote below, would this also be applicable if upon startup of a '86 turbo, the idle dropped to the 400-500RPM range and tried to maintain itself there ?

If your car starts, and then dies, on the first try, and after 2nd or 3rd time the car idles low then rises after its semi-warmed up, and the problem with starting only happens when the car is been sitting overnight or a long time, but is fine the rest of the day, then you need a new warmup regulator.

Two things can effect idle at startup. Air and Fuel! The WUR is just one part of a system. I could have swapped the WUR out on my car (~$200), but instead I bought a CIS tester ($50) and troubleshot to the real culprit.

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Bill Krause
'79 911SC Euro

Thanks everyone!!! I'm going to move forward and get new vacuum lines, routing them as indicated in the diagrams provided. I'm hoping to get this done today, as I'm heading out on a business trip tomorrow, and am anxious to see if this is the fix!!

Bill, by the way, my '78SC is in fact a European version, imported from Germany by the original owner in '82. I apologize if I didn't mention this before. I can personally testify to the ruggedness of these cars. Mine has almost 400,000km, and while most everything has been replaced mechanically, it'll hold its own against any car with low mileage!

On a side note, can I get the cloth-weave (?) covered vacuum lines at the neighborhood auto store? Are they necessary?

Thanks again everyone! I hope to post the results of our efforts later today.