Does anyone know what this sensor goes to?

[Squirrely Brother]

Evening,

I wanted to see if anyone had any idea what this sensor does or goes to. It was wrapped around the transmission coolant lines next to the passenger motor mount. The truck for the most part was not modified when I bought it, so I thought it might go to the alarm system I had installed. But, after trying to clean it I saw the wiring and sensor looked pretty old. I’ve tried Google with no success. If anyone could please help me out I’d appreciate it.

Thank you,
Alan


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[AuroraGirl]

possibly for an AC clutch? if the truck used to have a compressor on that side/a compressor at all. Maybe for a auxillary lighting harness thats not present like a plow hookup or offroader, but id think that would run driver side Unless it was a power cable running back, but its pretty thin. Am I to assume you have a 350 1981 federal emissions? If so you can try to look at your emissions setup the factory would have had, maybe match to a solenoid of some kind. Otherwise Im out of ideas!

 

[Squirrely Brother]

Aurora Girl,

Thank you, for taking the time to respond. The ac compressor is on the other side and works without issues. It is a 350 with a th350. I’ll look up the emissions diagram to see. I could swear years ago my 1969 Bronco had something similar attached to the block, but I can’t remember well enough. Again, I appreciate your help.

 

[Turbo4whl]

Looks like the knock sensor for the electronic spark control.

Would have been mounted in the side of block, (block coolant drain)

 

[AuroraGirl]

Looks like the knock sensor for the electronic spark control.

Would have been mounted in the side of block, (block coolant drain)

Im not familiar with all the 80s emissions devices. would an 81 have electronic spark control? I thought that came with electronic carburetors.

Of course, feel free to teach me if im mistaken haha. That would explain why ive never seen it.

 

[Squirrely Brother]

I think almost all of the emissions items were removed when I bought it. I started looking at a wiring diagram and it may be a detonation sensor/knock sensor per the diagram. There’s only a fuse panel. I don’t believe there’s a computer for spark control. I plead ignorance though.

 

[Turbo4whl]

Yes, the 1981 could have ESC. It was a stand alone system that was added, listen for a knock and retard the timing. The distributor was the same as previous years. The added system had a connector that matched module connector that plugged into the coil, and another to plug into the coil.

The wire going to the knock sensor is a coax cable. The whole harness back through the firewall to the control processor. This control mounted next to the parking brake assembly at the firewall. One more wire from the control to the fuse block for it's power.

 

[Squirrely Brother]

Okay. Thank you. I’ll check. The distributor was updated to an hei before I purchased. I only found the wire and sensor when I changed the motor mounts.

 

[AuroraGirl]

Okay. Thank you. I’ll check. The distributor was updated to an hei before I purchased. I only found the wire and sensor when I changed the motor mounts.

it should have been an HEI I Would think since its 81. 74 was the first year it was offered or it was made standard, HEI that is.

 

[Squirrely Brother]

I didn’t realize. I’ve had issues with the truck since replacing a cracked flexplate. Trying to clean up the entire engine compartment and found this random sensor/switch. Trying to figure out if I need to hook it up somewhere particular, if it can be eliminated or just leave it as is. The truck’s been a little discouraging lately.

 

[gotyourgoat]

Yes, the 1981 could have ESC. It was a stand alone system that was added, listen for a knock and retard the timing. The distributor was the same as previous years. The added system had a connector that matched module connector that plugged into the coil, and another to plug into the coil.

The wire going to the knock sensor is a coax cable. The whole harness back through the firewall to the control processor. This control mounted next to the parking brake assembly at the firewall. One more wire from the control to the fuse block for it's power.

I thought that was a coax connection on the side of that thing. Never seen coax on a vehicle though. Not familiar with that sensor or the system it works with. Are these aftermarket units or original options?

 

[Turbo4whl]

Okay. Thank you. I’ll check. The distributor was updated to an hei before I purchased. I only found the wire and sensor when I changed the motor mounts.

From your picture, the engine is not original because it would have been painted GM corporate blue. The original engine would have an HEI distributor. Goodwrench replacement engines were painted black but either way the engine has been out at least once.

I thought that was a coax connection on the side of that thing. Never seen coax on a vehicle though. Not familiar with that sensor or the system it works with. Are these aftermarket units or original options?

Standard equipment on early 1980's, at least on my '82, 305. Yes the coax goes straight to the processor with no other connection. Damage the coax, replace the whole unit.

Night time picture. Would have blue paint in the letters, which is long gone now.

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[SirRobyn0]

Im not familiar with all the 80s emissions devices. would an 81 have electronic spark control? I thought that came with electronic carburetors.

Of course, feel free to teach me if im mistaken haha. That would explain why ive never seen it.

Yes, an 81 could have spark control. And spark control can be with or without an electronic carb. I'll give you an example. My 1984 C20 has ESC (electronic spark control), but has a standard (non-electronic) carburetor. Had it been a C10 then I'm pretty sure it would have the electronic carb.

I will agree that looks like the knock sensor connector to me as well.

 

[Squirrely Brother]

The distributor only has the hot wire and vacuum. The wire on the connector is light blue and is routed behind the alternator to the harness. The truck is badges with spark control, but I didn’t see anything above the blower box. It believe from the factory it was originally a 305 with a 400 transmission. After tearing into it recently, I confirmed it’s a 90/91 350 with a 350 transmission. It has standalone hei, Edelbrock intake and 1406 carburetor since last weekend. The only emissions equipment I see is the charcoal canister routed to the tank vent and a catalytic converter. All else has been removed at some point. The sensor concerned me when I found it squirreled away. I’m starting to think it’s a sensor that’s not hooked up to anything and just hanging out there.

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[SirRobyn0]

Just as a point of reference for anyone that might read this thread in the future some trucks mine included do not have spark control badges, but did have spark control, so it's not like that's a requirement