Volvo Thermal timer wiring

Hi !
On Volvo MY 73 and 74, D-Jetronic uses a thermal time switch to pilot cold start enrichment injector. This device has two male connectors : one marked W (4.8 mm wide) and another marked G (6.3 mm wide). I can't figure out how these two connectors are plugged to injection loom.

One of the two female connectors coming from the injector loom has two wires (one to the cold start injector and one to the starter solenoid). The other female connector goes to the second cold start injector connector. One could have attempted that the two female connectors are of different width to accomodage the G and W different widths, but it's not the case...

The question is : which of G and W receives the starter signal that allows bimetallic spring to heat up ?

Resistance measurement between G and ground shows 45 Ohm ; between W and ground I measure 4.5 Ohm. 45 ohm makes me think about a coil resistance, so G would bbe the connection to the bimetallic heated spring. Could you confirm ?

Maybe G and W stand for german words and knowing those words could help ?

Hi, sorry - I don't remember your name.

Here is a schematic that will help you:  jetronic.org/de/kunena/jetronic/1896-the...esucht?start=6#18270

Regards
Norbert

So G heats up the bimetallic spring via the starter signal.

Thank you so much Norbert !

This is the first step to check the right behavior of the thermal time switch mounted on my Volvo 1800ES, which is quite long to start at cold temperatures. I will on a second step measure the voltage the cold start injector receives to check that the voltage is high enough to inject gasoline. 

Another point : on the volvo the cold start injector is directly activated by the thermal time switch. Apparently on others brands there is a relay between TTS and cold start injector. Can you confirm ? If I measure a quite low voltage on cold start injector it could be a nice improvement to install a relay triggered by the TTS.



 

Hi,

that depends on the power that the thermo time switch can switch. Early version cannot switch CSV, later can.

Thank you for your quick answer.

Voltage measurement shows only around 7 volts on the connections of the Cold Start Valve.
Wires resistance is below 0.3 Ohm for all concerned wires.

I now have two options to solve this issue :
- install a relay triggered by the TTS to open the CSV with a normal voltage
- use the Bosch electronic TTS

What is your experience about Bosch TTS ?

Hello,

here is a quick return of experiment about Bosch electronic thermal time switch.

Compared to VDO TTS, it is a bit longer, sensitive element length is a bit shorter and thread is identical. As original TTS is plugged to the Volvo engine with an adaptor, this means that you need to create an adaptor suited to Bosch TTS. A local machining workshop can  do it for you.

Electrically speaking, the connector is of a more modern design, Bosch standard although.

With this Bosch TTS, the Volvo has cold-started immediately. Very pleasant result.