Sensor Question on 87 XJ6

[Michael J.]

I have attached a photo depicting the rear of the water rail on my 87 XJ6 4.2 liter. There are three sensor switches visible in the photo.

The sensor on the right is for the water temp gauge. The sensor in the center is the fuel injection temp sensor. The thermotime switch is far to the right at the front of the rail and is not visible in the photo.

The sensor on the left at the rear of the water rail has two blade connectors The wires are bleached, so I am not sure of the color.

Can anyone tell me what this sensor is and what it does?

 

[Exotexs]

attached is a chart for the 4.2, Series III XJ-6 engine up to 1987, showing all the sensors and components.

Ex

 

[Exotexs]

I just realized that the last sensor is not shown there!

 

[jessebogan]

It is a temp sensor that controls the diverter valve for the air pump. When the car reaches a temp, it switches the air injection from the rail in the head back to the air filter. Basically, the air injection is used to heat the catylist more quickly, and then is no longer needed.

 

[Michael J.]

Anyone know how to test it? What symptoms are caused when it starts to fail?

 

[Deleted member 8987]

I would imagine put an ohmmeter across the terminals, start the car (leave the wires off and safe from shorting), and see if it makes contact at temperature.
If you are not comfortable with that, remove the wires (engine cold), measure the resistance across the terminals.

Remove the meter, re-connect the wires, drive the vehicle (or idle) until warmed up.
Shut off the engine, remove the wires, re-check with an ohmmeter and report back.

If you really want to get fancy, drain the collant down, remove the sender, place in a pan of water with a meat thermometer on a stove, with ohmmeter connected, and tell us the temperature when it trips.