What are the symptoms when the Thermo Time Switch goes bad?

If you have a 1989 US delivery Volvo, you do not have a thermo time switch. Thermo time switches were used on CIS and possibly other earlier styles of Bosch fuel injection. They had heating coils and a bimetallic switch and directly controlled the fifth injector. Your car has LH 2.4 Jetronic, if US delivery. It has a coolant temperature sensor. In the LH 2.4, the coolant temperature sensor is actually two sensors in one. It is an input to the fuel injection and the ignition. The coolant temperature sensor is a variable resistor based on temperature. Its input to the ECU controls the mixture. The fifth injector on your car should be disconnected, as I remember reading that Volvo has a service bulletin out to do such. A bad coolant temperature sensor will lead to poor starting, poor economy, rough idle, and poor power. The place to check the resistance of the coolant temperature sensor is at terminal 13 of the ECU. I don't have resistance values for the coolant temperature sensor for the LH 2.4, but for the LH 2.2 it is between 2,280 and 2,720 ohms at 68 degrees F. I think it is similar for the LH 2.4. There is additional information in the 700/900 FAQ.

Right On! you got that stuff nailed down my man!!

Thank you. I don't think the other paries responding to the original post understand what a thermo time switch, and what a coolant temperature switch is.

On a K-jet, say a turbo, the symptom is too much cranking to start. Period. Running is fine. Hard start and a minute or so of poor running and stumbling is more like a CPR (control pressure reg) failure. This is on K-jet, mind you.

Commonly, the wires fall off the thermal time switch because the connector degrades or some mechanic decides not to hook it back up after doing something else.

I'm not sure you have one on an 89 LH though since there is no 5th injector. If you do, I am not familiar with ts failure on those cars.

this controls the 5 injector in your car , the cold start injector. . The 5th injector is used when the engine is cold, and hence at start up more fuel is pumped into the cylinders so we warm up fast.

If it goes bad ( the thermo time sw) I would say that as soon as you start up and and you put the car in reverse or drive, it can stutter or possibly die. You will find that you need to wait like a minute or so after starting on a cold day, before you can engage the drive/reverse.

Your correct if it fails and never closes. It is supposed to close only as long as the engine coolant is under 50 F. If it fails to open the engine will start cold and run fine when cold. As soon as it warms up it will run rich, smoke etc. If so try disconnecting the wires when warmed up. Of course it is more likely the wiring harness has failed then the thermo timer has gone bad.

Bill D.

you are right, did not think about the effect when the swicth stays closed all the time and leaves you with a permamnetly on 5 th injector !!!.

Also in testing it is probably much easier to disconnect the wires at the injector instead of at the thermotime switch. They do make a test light to see if injector is getting power. I believe they work on 3-4 volts and will not illuminate a 12 volt test lamp.

Bill D.