Red sensor on intake

[DaemonForce]

Near the front facing the top...What is this and what does it do? More importantly, if I wanted to replace it with a newer one, where would I get it?

[eagleman]

Don't know either but sure am interested in finding out also! When I had my intake and exhaust manifolds off to replace the two busted off studs I removed it and cleaned it on the wire wheel and reinstalled it I wondered what it was and what it did in the skeem of things. Hopefully know we'll both find out. Glad you ask.

[AMC of Houston]

Like Dave said; a pic would help.   If its a 1984 or newer, it could be the knock sensor (according to my parts manual).

[DaemonForce]

If its a 1984 or newer, it could be the knock sensor (according to my parts manual).

Red thingy between 2 and 3.

[ammachine390]

Yep, its the knock sensor.

looks like a temp sensor. either air or water. never heard of a none efi car to have an air temp sensor tho...

Actually, Eagles have an air temp sensor in the back of the air cleaner box.

[DaemonForce]

looks like a temp sensor. either air or water. never heard of a none efi car to have an air temp sensor tho...

Stock air cleaner had at least one. Gave me at least one reason to get rid of it too.

Actually, Eagles have an air temp sensor in the back of the air cleaner box.

It doesn't relate to vacuum and it has a probe. It's definitely temperature related but because all the wires to the manifolds are shielded I can't trace what goes where. It would be useful to at least know WHAT they are rather than to just tear everything out while hoping I can replace stuff. Oddly, I've been getting weird ideas for fuel injection lately so there's a good chance a lot of this matters a great deal. Would a 4.0 intake bolt straight up to the 258 head without remachining? Does it have some evolution of these sensors?

[BenM]

It's the knock sensor. It actually detects sound with a tuned crystal.

[carnuck]

My knock sensor is on the block. I recall that is the IAT (intake air temp) sensor that turns on the manifold heater.

[ammachine390]

My knock sensor is on the block. I recall that is the IAT (intake air temp) sensor that turns on the manifold heater.

Isn't your Eagle an 82? They didn't put knock sensors on Eagles until 1983. Are you sure you are not thinking of the temperature sensor for the temp gauge located on the back of the engine block? The manifold heater temperature sensor is located on the side of the of intake manifold, not on the top.

[amcinstaller]

i would think a knock sensor would be quite useless in an intake. block makes more sense. and iat makes more sense for that

[BenM]

I'm pretty sure it's the knock sensor. It wasn't used on every engine. The temperature sensors (some may be three-wire) go in to the coolant passages at the bottom of the manifold, and early cars without aluminum intakes will have vacuum switches in the coolant jacket in the side of the block.

[Eagle1985]

The AMC parts catalog shows the knock sensor here: http://www.amceaglenest.com/~iowaeagl/guide/index.php?title=Section_12%2C_Manifolds_and_Carburetors

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[DaemonForce]

It's the knock sensor. It actually detects sound with a tuned crystal.

I'm not sure what's worse, the diagram proving this or the fact that when I read "tuned crystal" that the old crystal radios come to mind. God that's old! O_o

[eagleman]

Don't know bout you but now I'm really corn fused! Crystal tuned, say what? Haven;t been able to get any radio stations on it yet but I won't give up either lol. Seriously would just like to know what it is and what it does besides confuse most of us.

[BenM]

It's just a tiny microphone-like device to let the ECU know it needs to retard the engine timing to prevent knock.

It detects a high-frequency sound by direct contact with the intake manifold. I'm not sure why it's there and not somewhere else, but it must have worked well enough.

If you want to know how it works:
http://www.engineblox.com/?p=65
http://en.wikipedia.org/wiki/Piezoelectric_sensor