Thermo time Switch testing
 

My Thermo Time Switch (marked with 15 C marking) measures 2700 ohms at 16degree C. Is that good or bad?

I would expect it to be near zero.

Is that your vac switch behind the TB or the CSV switch in the cam cover? The latter should have no continuity when warm.
Alan

It is the one in the timing chain cover and it should have continuity when COLD, so that it turns on the Cold Start Valve. That is the theory, I think. It does increase in resistance when warm.

Yes, that one should provide a circuit to the CSV at start up, the circuit should break as soon as it warms slightly. Should be zero ohms, rather than 2700. You could pull it and place it in warm water , eg 20 deg and see if it opens completely.
Alan

I did that. and it does not close completely at all. It never did open completely either but at 2700 ohms that is close to an open circuit for automotive current switching use.

Are you testing the switch without any wires attached? If not, you will also be measuring the windings in the CSV.
Alan

The switch is tested on the bench, by itself.

Drop it in some warm water and see what happens - it should go to zero ie open the contacts.
Alan

I bet you are testing between the 2 terminals the wires go on.
test from each terminal to the body or threads of the TTS

when it is cold, terminal W should be zero ohms to ground.
the other terminal to ground should be higher, I am guessing 2700 ohms based on what you have done,

when warm, the W terminal should be open to ground, or the body
the other terminal may be higher,

I don't know off the top of the head which terminal it which, but cold, one should be 0 ohms, the other much higher

That sounds about right. The wiring diag is a bit complicated (for me) as to the internals of the sw. But a Yellow wire feeds from the starter solenoid to the CSV then on to the sw (G). This has to be the power feed to the solenoid coil in the CSV. It then needs an earth to activate the coil feed. A r/bk wire runs from the other side of the CSV to the sw (W). I am guessing this is the earth. W to the body should be on/off as far as ohms go with temp. That is my best guess.
Alan

So what is the function of the other pin on the TTS?

it takes the Yellow wire which is the power feed. The wiring diag does not explain (at least to me) what the internal symbols mean inside the sw that this wire feeds to. But it must have something to do with the 2700 ohms. According to the diag, there are some internal components in the sw. Maybe some sort of heating circuit or something? I thought the oil temp served as the heater, but maybe not. May be an internal system.
Alan

Probably a heating circuit because they want the switch to open up and stop the cold start injector a few seconds after the ignition is switched on. If you rely on the engine to heat up the element, then it would take too long to stop the CSV.

My guess.

I was thinking down that line too - but the CSV is only powered by the starter solenoid - ie while cranking. The purpose of the switch is to allow the CSV to work on cold start up, but you don't need the extra fuel on warm start up (you still have a WUR which is enriching the mixture as the engine cools from hot to warm to cold.)
Pictorally I wonder if they are displaying resistors on the Y wire circuit side. But the diag is too vague, or my knowledge too poor to understand what they are trying to depict.
Regards
Alan

I don't even know what car yelcab1 is talking about.

Is it the 2005 GT3?

If it's an older car. Starter engagement only. At a certain temp which I thought was 115-ish F, open circuit. Under that. CSV sprays when starter is cranking, but only then.

15C? You sure you got the right sensor?

No Bob.

It is a 1991 965 Turbo.

THe schematic does show that the heating elements (2 of) are energized only while cranking. My guess is if for some reason your cranking is prolonged, the heating elements will heat up the thermoswitch and turns off the CSV.

Maybe they shorten the spray duration as well if it's only partially warmed up and then restarted?

Rambling here..... I worked on a 77 XJ12. It has a Lucas system licensed from Bosch. Uses manifold pressure for primary control. However, has two CSV's controlled by one TT switch. It will taper off the length of spray when the starter is engaged as resistance rises in the TT switch. It does not have a second sensor. I wonder if your 15C sensor extends the spray length capability if under 15C (59F). 1991 is way more advanced than my 81 so rambling is all I got without real study.

Probably best shot at a logical answer. After all it is only designed to work as a simple on/off sw. So the idea of adding another layer of complexity could only be to 2nd guess another situation. Prevent flooding/hydraulicing a no-start engine?
Alan

Cripes, where's Ronnie?:(

Just talking. I bet it is twofold. Prevent flooding and taper off duration of spray as temp increases.

Hydro lock is probably not a risk as unburnt gas is in vapor form and lots will be pushed into exhaust as engine cycles. Then there is the risk of way too much petrol in the exhaust system. Aside from cat damage, I do not know what the worst risk is. Could an explosion occur?

Less likely for an explosion, but the cat will glow red hot.