CIS circuity question

[ahdoman]

Ref; 73.5, 2.4CIS motor - I'm having some problems figuring out just how to wire the CIS system. I have both a thermal time switch (in the left cam gear cover) and a small micro switch that sits on the throttle body. I think I only need one or the other? They seem to do the same thing; in theory the thermal switch activates the cold start injector or the other option is with the micro switch when I start the car I step on the gas a little to activate the switch? Is this correct?

Also - Does the WUR only need a switched hot lead?

[Walter_Middie]

While the key is in the run position, power will be sent to the WUR if the Thermo-Time Switch allows it. On the left side chain cover is the Thermo-Time Switch which is the basic control for the enrichment solenoid during the starting phase. If the car is warm from running recently, or enough time has elapsed since it was started, the Thermo-Time Switch will interrupt the power going to the WUR.

The cold start valve itself has a grey and white wire and a red and black wire from the thermo-switch: Note that the gray and white wire and the yellow wire are connected to the same terminal on the thermo-switch. The WUR (warm up regulator) mounted on an intake runner base on the driver's side of the engine should have a single red wire with white stripes connected to it.

Cold start valve circuit: There should be a wire from the ignition switch to terminal 50 on the starter (this is a small blade type lug that receives a female type connector), from terminal 50 of the starter a wire (yellow) goes to the throttle valve switch. From the other side of the throttle valve switch a wire (also yellow) goes to the thermo-switch on the driver's side chain case, this wire from the throttle switch attaches to one terminal (this is the non-ground side terminal) of the thermo-switch, a second wire is also attached to this same terminal of the thermo-switch and goes to the cold start valve. From the other side (ground side) of the thermo-switch a second wire goes to the cold start valve.

[HarryD]

Rex's description is correct for later cars. The 1973.5 CIS did not have a thermo time switch.

For starting, you fully lift the hand throttle (the black handle next to your seat). This does two things, it opens the throttle plate a bit and, when full up, closes the microswitch on the throttle body. The switch is powered by the voltage to the starter motor when you crank the starter. The power is used to turn on the Cold Start Injector on the throttle body to enrich the mixture during starting. When you are not crankinghte starter, there is no power to this injector.

The correct starting procedure is discussed at length in an earlier thread. Grady Clay has some good comments.

So, ahdoman, you do not need the thermotime switch but you do need a functioning hand throttle, properly adjusted microswitch, and the cold start injector working.

This is the circuit for the WUR:

This is the diagram for the Cold Start Valve (item#12):

You can find all of the electrical drawings here: Pelican Parts - Porsche 911 Parts Listings & Diagrams

[ahdoman]

Thanks Harry. That's what I was thinking. Although I still don't understand the need for the microswitch. Is it hooked up to the hand throttle only? That way when the engine is warm and you don't pull the handle you don't activate the injector?

[HarryD]

Originally Posted by ahdoman

Thanks Harry. That's what I was thinking.

Glad to help

Although I still don't understand the need for the microswitch. Is it hooked up to the hand throttle only? That way when the engine is warm and you don't pull the handle you don't activate the injector?

This may help:

Originally Posted by Jim Sims

Correct starting procedure for a 1973.5T from an old post:

The owners manual for a 1973.5 CIS states that the hand lever should be pulled fully up (so the micro-switch on the throttle body closes and sends power to the cold start valve) for all starts when the engine temperature is less than "very high". Very high is defined as an engine temperature of 212 to 250 F. Unless the engine is running hot and the stop is very brief (so the engine doesn't cool off) this in a practical sense means the lever is pulled up for every start. The manual further states that when the ambient air temperature is below -5F the lever should be fully pulled up and the gas pedal partially depressed; then when the engine starts, the lever is positioned for a 1200 RPM warm up speed. For "nominal cold starts" (air temp above -5F and engine oil temperature below 155F) the lever should be pulled fully up without gas pedal application and then once the engine starts the lever is lowered to set the engine RPM at 1200 for warm up. When the engine is warmed up (~155-160F oil temp) the lever is fully lowered. When starting a warm (as opposed to a "very high" temperature) engine the lever is pulled up for starting and immediately pushed back down after the engine starts. For the very high temperature case (212 to 250 F oil temperature) the hand lever is left down and the gas pedal is fully depressed during starting. It is important to note that the '73.5 and (also the 1974?) CIS cold start valve (CSV) circuits do not incorporate a thermal time switch so the driver has to control this function. Note though that as usual the CSV only operates while the starter is turning, it does nothing for cold running after that time.

Note that in some of these cars this lever may do nothing as an attaching plastic link to the throttle rod in tunnel may have broken or the micro-switch on the throttle body is broken, out of adjustment or disconnected.