Mystery coolant sensor/switch

[skidd1000]

I was looking under the hood of my '91 today and noticed a sensor in the intake manifold, drivers side,directly under the fuel pressure regulator that does not have any wire going to it. I searched high and low but do not see any extra wire that should be plugged into it. It appears that it has only one pin on it for a single wire. Everything works on the car. Anyone know what this sensor is.

[Barney Eaton]

The only thing in that area is the coolant temperature sensor. 

If possible post picture

[skidd1000]

Hello Barney. It is definitely a coolant sensor.The only other coolant sensor I see is mounted directly below the throttle body/maf and it has a pair of yellow and black wires going to it. My gauge works perfect and the fans come on with the a/c. I will try to post a picture in a bit.

[skidd1000]

Here is a picture. The sensor is just below the vacuum lines.

[2seater]

Interesting. I have the same manifold on my '90, and that is where my temperature sensor is located, black and yellow wires connected to it. I couldn't see below my throttle body due to my turbo down pipe, but I do think there is a port there as well. I suspect it is a universal fit that may use two different sensors for the gauge and fan use, and have seen that before on GM cars. The earlier manifolds have multiple ports too. For those that don't know, the L27 fuel pressure regulator is located at the rear corner of the manifold, rather than up front as on the LN3.

Edited May 6, 2018 by 2seater (see edit history)

[skidd1000]

Thanks, 2seater. I too find it interesting that gm would put in a sensor to fill that hole instead of a simple plug, but hey... as long as everything is working I'm not going to worry about it.

[Barney Eaton]

There is a black and yellow wire running past the sending unit.......is there a connector tucked under that metal bracket?

[skidd1000]

Hi Barney. Yes the black and yellow wires are plugged into the other coolant sensor under the throttle body/maf.