jrogers

I seem to have my 930 sufficiently rich now where I am not getting detonation (3-3.5% CO) but now I am too rich for the first few minutes of startup. Looking at the service manual, I see there is a warm up system that uses two resistors, essentially as timers, and changes the pulse timing to richen it up for the first few minutes. What this results in for me is lots of black smoke, and fouling if I get on the throttle too far. If I understand this correctly, there is a 15 deg C and a 35 deg C sensor thatcontrol this. My question is, how do I disable this? Can I just gound the 35 deg wire to override this system? Is this a good idea? I don't imagine that I will have a cold start problem as rich as it is running. Any suggestions would be appreciated.

FLYN930

I don't mean to hi-jack your thread here Jim, but I was just performing my first valve adjustment on my '81 930 and noticed that my thermo-time switch was unplugged. Not just one wire, but both wires were disconnected as if it were done on purpose by the previous owner/mechanic. So, not thinking too much of it, I hooked it back up and notice no difference in startup at all. It fires right up and idles at about 950 RPM regardless of temperature. Of course, I'm in southern California where it's always 75°F. My question is: What would disconnecting the thermo-time switch do?

jrogers

No problem. This will give me a chance to say what my understanding of this is, and give others a chance to correct me. This is a two stage enrichment system, with sensors at 15 deg C and 60 deg C. This translates to 54 deg F and 140 deg F. I would agree with you that the first stage at 54 deg F rarly applies to you.

I have not yet checked the temp sensors to see how they work, but if they are normally taking the curcuit to ground when cold, then unplugging them will essentially always disable this system. When you plug them back in, you may not notice much of a change, since it is only the second stage that will effect you, and I think it is only operational for two or three minutes. Also, it does not change the idle, but changes the pulse duration, which increases rate of fuel at the injector, thus increasing the richness. In my case, my idle stays the same, but I see it in the form of black exhaust from being too rich.

Hope this helps. When you say they where unplugged, I assume that you mean they where just unhooked and taped up, or something like this, not grounded, right?

FLYN930

Thanks for the info Jim. The wires on my car were disconnected but not grounded to anything. Because I didn't notice any difference after hooking the switch back up, I went ahead and ordered a new switch from the dealer thinking it might be bad, hence the reason it was unhooked. Oh well, maybe it won't make any difference at all. I'll guess I'll find out this weekend when I have a chance to install it.

Brian

jrogers

Brian,

What is the switch that you are hooking up? Is this one of the temp sensors? One is located on the chain case, I think, and the other is near the breather at the top of the engine, towards the front. If this is a temp sensor you are changing, you should be able to test it with a multimeter and a pot of water. As it warms up, it should change states (open to closed, or closed to open) when it passes through the rated temperature. Let me know if you notice any difference after you change this out.

FLYN930

From what I've been able to learn from various websites (this one included!) it's the thermo-time switch that's located on the left-hand chain cover. That's what I found was disconnected on my car for reasons unknown. Now I'm curious to take a look at the other temp sensor you mention too. Maybe when I get home from work tonight I'll have a look. I will also test my old thermo-time switch before I replace it with the new one using the "pot of water on the stove trick" and see what happens. Thanks Jim.

Brian

KeithC2Turto

jrogers

Could you be trying to work around somthing else that is not working right?

Might want to make sure your car is in good tune first and that all systems are working ok.

A couple of things that I'd think that might creat pinging would be. Carbon diposits on the head from runing to rich. The retard unit on the distributor is a posibility. And a malfunctioning WUR that is not adding fuel on boost.

Just a thought!

For richnes on start up the WUR effects this also. The WUR can be adjusted by someone that knows what they are doing to make it richer or leaner on start up.

It has a bi-metalic strip that is heated up by the wires that go to the WUR. Thus strip is what adjusts the control presure so that the car will run richer when cold. I think it is monunted on a pin.

The pin can be dirven in further. I don't remember if this richens it or not. If it is dirven in to far - you have to take the WUR apart and drive it back out. This may be what you need to lean it.

There was an artical in the Fixin Up Der Porsche book about how to replace the pin with an adjustable bolt so you don't have to take it apart if you go to far.

Any way, you would not want to disconect the thermial switches. I belive these work by completing a circt to ground when the temp rises above a given level. If any thing, you'd want to remove the wire and hook it to ground so it thinks it is hot.

If your system has the "Acceleration Enrichement" function like the C2 Turbos, there are two wires that come our of the Ox Control Unit that become grounded when the throtle is opened. This happens mostly during the first 2 min and it bumps your frequency valve up to 75% and 50% from about 45% to add more fuel for dirvability.

Do you have three box's under the divers seat? If so the terminal 12 on the Ox control unit or terminal 14 on the Acceleration Control Unit might be the wire wire it grounds to triger the richnes during the first 2 min, at least on a 91/2 C2 Turbos.

Good luck and keep us posted!

Keith

Dean

Ok, I just had the same problem as you. Rich as hell on cold starts. What I did was I pulled the pin out a little on the WUR. I did it by drilling and small tapping a small hole in the pin. Then I used a small screw and washer to pull the pin out. I went too far and it is too lean on startup. So now I have to tap the pin in a hair to get a good startup

jrogers

Thanks for the info, guys. If anyone else is interested in this, I did find some form of this article on-line at <a href="http://www.pelicanparts.com/techarticles/911_warmup_reg/911_warmup_reg.htm." target="_blank">http://www.pelicanparts.com/techarticles/911_warmup_reg/911_warmup_reg.htm.</a>

My manual does talk about changing the pule timeing for acceleration enrichment. Do these two systems work together? Is the WUR out of the picture after the first three minutes?

By the way, the detonation is gone. I retarded the ignition, which I may not have had to do, since I found that the O2 sensor had gotten hooked back up at somepoint, so I unhooked it again. Carbon deposits should not be the problem for me yet. The motor is a fresh rebuild from this winter, and has about 400 miles on it so far.

If I can just get it to run good these first few minutes, I would be happy. I will look into the adjustable pin. I am still trying to figure out if pin in (they easy way) is leaner or richer...

Thanks again,

Dean

The farther the pin is in the richer the warmup mixture. I forgot to mention that you should have your fuel pressures looked at. Because you also might be too rich when warm also. The WUR controls both cold and warm fuel pressures