Cold Start '7 7CIS
 

So my 77 911S starts a bit hard cold. It'll spit and sputter, sometimes die. It'll all the sudden rev high and run about 1800rpm or so and gradually come down to 1000rpm as it warms. So I thought I would do some checking. The TTS gets conductivity across its terminals with the engine cold or warm. Should this be correct? I get conductivity at the terminals on the TTS and the CSV valve. I pulled the air filter and opened the pop-off valve and hard my wife turn the key. I saw no mist or evidence of gas. I may not have been looking in the right spot. But knowing this, does it help diagnose?

Thanks in advance,

Nathan

Did she turn the key to start the car or just to on?
The power to the CSV is only sent on a start.

Hook up a pressure gauge and test the CIS pressures as explained in many posts and manuals.

Check for air leaks. (Vacuum)

Do an advanced title search on CIS cold start.

turned to start. I pulled the coil wire so it wouldn't start. Pressures:
Valve closed pump running pressure is what? (system pressure) 4.5 bar

Valve open pump running pressure, wur unplugged pressure is?(cold control pressure) 1.5 bar

Valve open pump running wur plugged in pressure?(warm control pressure) 2.3 bar

Valve open after warm pressure check, turn off car and residual pressure reading immediately and after 30, 60, 120 seconds and then 15 and 30 minutes? 1.8 bar immediately, 1.5 bar @ 30 secs, 1.5 bar @ 60 secs, 1.4 bar 120 secs, 1.1 bar @ 15 min, & .9 bar @ 30 min

Should I see continuity across the switch, both cold and warm? When I open the pop-off valve, should I not see some evidence the CSV is firing?

Power flows to csv when starter is engaged. The power goes to the csv yellow wire. Ground wire from csv to tts. Tts should be open when warm. So turn key engage the starter if engine is cold tts will let the csv operate. If engine is warm tts opens circuit and csv won't operate. If you read continuity from the tts to ground and engine is cold you will show continuity.

I'm reading continuity across the TTS terminals when both warm and cold. I did not disconnect its wires though when I checked continuity.

Remove the wire and then check. If the terminal to ground shows continuity then if you have power to the csv then it should work when the starter is engaged.

warm control pressure is too low. if mixture was set warm, then it will be too lean when cold.

if it is starting, i would lean towards the CSV circuit working. problems after it gets started are fuel pressures, mixture, and air leaks.

also, make sure the ignition is in proper working order.

you also need to check the TTV (thermo time valve). it makes the mixture richer when cold, for about 20 seconds. 2.3 bar is low, and even more low if the TTV is working. you should have around 2.8 with out vacuum to the WUR and around 3.4 with vacuum.

conductivity(across the terminals) and continuity, don't get them confused. measure voltages with respect to ground. continuity would be more related to resistance (ohms).

Thermo-time Switch Test........
 

Nathan,

Pull out the TTS from the engine and test for continuity. Both the small (G) and large (W) terminals are grounded and have continuity between them below 45°C/113°F. Above this temperature, there will be no continuity between them and no ground contact (body of the TTS). Use a cigarette lighter or candle to heat up the TTS for a few seconds until the continuity disappears. Or dip TTS body in iced water to close the ground contact. Keep us posted.

Tony

Continuity test.......
 

Nathan,

With both wires connected to the TTS, there will be continuity between these terminals at all times (cold or warm) provided the CSV is in good working condition. To test the TTS, disconnect both wires and check.

Tony

That makes some sense. I'll try to get a chance to remove the switch tonight and try. When I have the ignition engaging the starter (wife's job) and I am looking into the pop-off valve, what should I see to know that the CSV is working?

CSV inspection......
 

Nathan,

You won't see anything helpful into the pop-off valve. The CSV valve is energized when you turn the ignition switch to START. To test your CSV, you need to pull it out and place it in a small glass jar while cranking the starter. Watch out for the mist-like spray pattern of the injected fuel. With the engine installed, it would be very difficult to do this test (visual) unless you have a special fuel line or extension to bring the CSV out to the front of the engine. Or test it to see if it is working by leaving it in a container at rear side while cranking. Keep us posted.

Tony

As Tony mentioned, make sure your ignition components are all working correctly, especially your points.

no points, I have a pertronix unit in place.

In that case I'd go w/ what Ty (T77911S) recommended. Make sure the control and fuel pressures and mixture are correct. Sounds like your cold start is just a little off. The warmup cycle should, of course, be to immediately go to the high rev and then gradually fall, which yours eventually does.

As Tony mentioned, make sure all other ignition parts are up to spec, and verify no vacuum leaks.