CIS cold start issue

[brighton911]

I'm working on a neighbors 74 911, symptom is very poor cold starting, needs starter fluid every time (yikes). Runs fine once started and warms up as it should. Anyway, thermo time switch checks out OK BUT there was a fiber sealing washer on/under it. Seeing how it the system works, if the switch is not grounded, it won't do it's thing either heater or grounding the feed to the cold start valve - right? Secondly, I'm not CIS guy, where the heck is the CSV? I can't even see it using a mirror.
Side story, I see his car on my bike rides and stopped in to meet him. He said it quit last year, loud clang clang from the engine. He wisely flat bedded it home and it sat for 9 months. Had a look this week. Number 3 exhaust rocker fell out when the cover was removed. Shaft had walked out. And better still, 3 other rocker shafts were on their way out too. But he really got lucky, no damage to anything except for a tiny nick on the rocker bushing right at the outside edge. Getting lucky is a good thing.

[theiceman]

yeah i had one recently walk out too. another good reason to make sure you stay on schedule for your valve adjustments. Stuff like this can be easily checked at that time. bet it was leaking oil like a sieve. ( the first obvious sign )

doesnt the 74 use a manual control for cold starting that holds the throttle open a little ? my buddies has this , but maybe someone added it after.

[ossiblue]

The CSV is located on the front of the engine (side facing the firewall), as shown in the picture, below



Being a '74, the fuel pump will run when the key is turned ON, unlike later cars that have a fuel pump relay. Instead of using starting fluid, turn the ignition ON, and gently lift the sensor plate in the intake, behind the air filter. Hold it for only a couple of seconds or until you hear/feel a vibration of the injectors as they shoot fuel into the cylinders. The engine should now start.

Pull the plug off the CSV, and see if power is getting to one terminal during cranking, and a ground is at the other--don't forget to pull up the hand throttle in the cab as the hand throttle not only opens the throttle a bit but it also closes a micro-switch that provides the ground to the CSV. If you have both power and a ground, pull the CSV from the engine and see if fuel in being injected when engine is cranking.

[Bob Kontak]

Originally Posted by brighton911

Anyway, thermo time switch checks out OK BUT there was a fiber sealing washer on/under it. Seeing how it the system works, if the switch is not grounded, it won't do it's thing either heater or grounding the feed to the cold start valve - right?

I don't think the switch body is required to be grounded to the case for it to function.

If it is required to be grounded it is grounded through the threads.

[brighton911]

Thanks for your help guys. Duh, of course it will ground through the threads! I'll follow the path suggested by LJ on tomorrow's start er' up session. I have already checked for the correct operation of the hand throttle and the micro switch so not too much left to check.

[brighton911]

I bench tested the TTS and I think I may have found the problem. It appears the terminals W and G are not electrically isolated from each other. Feeding 12 V to G, the ohmeter (connected to W and the body) blanked out - weird. So I switched it to the volt scale and I was surprised get 10.54 volts on terminal W (both voltmeter and neg. from battery are grounded to the body of the TTS). So, the TTS is never supplying a ground to the CSV because it is cross feeding almost 12 V to terminal W. The heater circuit does work but the resistance across W and ground goes from zero to a max of 95 ohms - that is with the power to W disconnected. Correct me if I've got this wrong.

[Bob Kontak]

Originally Posted by brighton911

I bench tested the TTS and I think I may have found the problem. It appears the terminals W and G are not electrically isolated from each other. Feeding 12 V to G, the ohmeter (connected to W and the body) blanked out - weird. So I switched it to the volt scale and I was surprised get 10.54 volts on terminal W (both voltmeter and neg. from battery are grounded to the body of the TTS). So, the TTS is never supplying a ground to the CSV because it is cross feeding almost 12 V to terminal W. The heater circuit does work but the resistance across W and ground goes from zero to a max of 95 ohms - that is with the power to W disconnected. Correct me if I've got this wrong.

I think the TTS is a gate for electricity to be allowed the flow through or not be allowed to flow through depending on temperature.

The terminals should talk to each other if under the temp cut off point. Then no.

Let someone else confirm. I don't have diagrams in front of me.

[boyt911sc]

Originally Posted by brighton911

I bench tested the TTS and I think I may have found the problem. It appears the terminals W and G are not electrically isolated from each other. Feeding 12 V to G, the ohmeter (connected to W and the body) blanked out - weird. So I switched it to the volt scale and I was surprised get 10.54 volts on terminal W (both voltmeter and neg. from battery are grounded to the body of the TTS). So, the TTS is never supplying a ground to the CSV because it is cross feeding almost 12 V to terminal W. The heater circuit does work but the resistance across W and ground goes from zero to a max of 95 ohms - that is with the power to W disconnected. Correct me if I've got this wrong.

Brighton,

At temp. 113°F and below, the heater is grounded. Terminals G and W have continuity between them. But at 113°F and above, the heater is not grounded (open) and the continuity between G and W is now also gone. Use a continuity tester to confirm and verify your test results. The typical heater resistance in the TTS is about 24 +/- Ohms.

Tony

[brighton911]

Thanks Tony Resistance between the two terminals is 23 cold rising to a max of 38 ohms no matter how hot the TTS bulb is. Resistance for the heater circuit to ground is cold 23 ohms, hot 57 ohms.

Dave