its down by the starter, below the plugs, twards the back, since i ahve my exhaust off im gonna replace my starter and anything else that might be impossible to replace when the exhaust is back in

 

Sounds like you're talking about the knock sensor. Does it have just one single wire going to it? White even? It is a pain to get at so... They cost around $50 Canadian so.. Not sure what they are in US funds. If you are that particular then yes change it.

HTH
Keiran

 

My '90 RS 305 has 2 sensors there. One larger-in-diameter one is knock sensor - the other one is a tad bit higher, a tad more forward, smaller in diameter, and is the Fan Switch.

Hope that helps

 

That is true, but the Fan switch is on the Head itself, not the block.

 

Yup, knock sensor is in the block about an inch above the oil pan, in a hole that we didn't realize was the knock sensor hole from 55 to 81, we always thought it was a coolant drain; and the fan switch is in the head between the #6 & #8 plugs. Quite a ways apart.

If you decide to replace it, be prepared to deal with the entire contents of the cooling system coming out there; and put it back in with about 5 wraps of Teflon tape, don't use silicone, don't drop it or bang it with anything, and above all don't overtorque it!!! 10-15 ft-lbs is entirely enough with the Teflon tape.

 

I don't doubt I'm wrong on the location of the Fan Switch - when I replaced mine it was dark, the hot coolant gave me a slight attitude problem when it burnt my arm, then splashed on my worklight and blew the bulb. By that point, my my weak flashlight batteries where lucky to find the hole at all!

LOL - the pains we go through to get from point A to point B!