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whats this plug?

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Old 10-09-2018, 10:37 PM
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Car: 1991 base firebird
Engine: tbi 305
Transmission: 700r4
whats this plug?

im chasing what feels like a fuel issue but may not be. I changed the fuel filter and am now changing plugs and wires. when I was under the car doing the plugs I saw this guy hanging there. this is under the passenger side over the starter. there is a brass plug screwed into the block. maybe a knock sensor?




maybe a knock sensor? I believe it goes there. im not sure how it connects though.
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Old 10-09-2018, 10:42 PM
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Re: whats this plug?

Fan switch plug.
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Old 10-09-2018, 10:43 PM
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Re: whats this plug?

Originally Posted by Evilokc View Post
im chasing what feels like a fuel issue but may not be. I changed the fuel filter and am now changing plugs and wires. when I was under the car doing the plugs I saw this guy hanging there. this is under the passenger side over the starter. there is a brass plug screwed into the block. maybe a knock sensor?




maybe a knock sensor? I believe it goes there. im not sure how it connects though.
there was a guy hanging under the car ? Lol
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Old 10-10-2018, 05:42 AM
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Re: whats this plug?

Looks just like a knock sensor plug to me.

Last edited by 3.4 grape; 10-10-2018 at 05:47 AM.
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Old 10-10-2018, 08:53 AM
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Re: whats this plug?

Originally Posted by 3.4 grape View Post
Looks just like a knock sensor plug to me.
If you look at the picture supplied by the original poster , in the area of the back of the starter motor (which faces the front of the car) you'll see that the knock sensor does have a very similar connector already plugged into it . So if the knock sensor is already plugged in , that hanging connector has to be for the temperature switch for the radiator fan , since both units use a nearly identical looking connector (irrespective of the color of the plastic , a close look will reveal that the connectors are in fact pretty much the same) .

PS , the biggest clue of it being for the electric radiator fan is that is has a green with white stripe wire attached to it , which the wiring diagrams indicate belongs to the fan ......

Last edited by OrangeBird; 10-10-2018 at 09:01 AM.
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Old 10-10-2018, 06:26 PM
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Car: 1991 base firebird
Engine: tbi 305
Transmission: 700r4
Re: whats this plug?

I ordered a new fan switch . my wife took the car out today and it overheated. I hope it didn't do any damage I will install the fan switch tomorrow and go from there.
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Old 10-11-2018, 08:23 PM
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Re: whats this plug?

Yup, fan switch.

You can see the knock sensor sitting there, all plugged in. Definitely not that.

Fan sw goes in the head between the #6 & #8 spark plugs.

I'm guessing your car has suffered a motor swap (sodomy) somewhere in its growing-up pains, possibly along with some other "improvements" of whatever sort?
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Old 10-11-2018, 09:06 PM
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Car: 1991 base firebird
Engine: tbi 305
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Re: whats this plug?

nope. its still the original 305 tbi motor. very few improvements either. pretty original car. its just old and needs some love. im slowly bringing it back
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Old 10-14-2018, 05:53 AM
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Car: 1986 IROC-Z
Engine: 305 TPI
Transmission: 700R4
Axle/Gears: Presently Open w/3.23 Ratio
Re: whats this plug?

I agree that that plug is likey for the coolng fan.looks famaliar.

Please note that the fan switch has nothing to do with the gauge on the dashboard
which is controlled by a seperate sensor typically on the driver side of the block and has
only one wire near cyl 3.

Just saying as in another thread you mentioned on engine startup you saw 220F on the gauge but the engine felt cool.
Also you mention above that you were told it overheated. Per the gauge or actually boiled over?

2 different things. Might be a good thing to check that sensor and clean up the connection in any case.

Hope that helps

Last edited by TAbracadabra; 10-14-2018 at 06:33 AM. Reason: Correct caps and add detail
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