Canister Purge Solenoid

1991vert · Jan 22, 2009

How does the charcoal canister purge solenoid work? There are two wires going to it: Grey/Yellow and Red. I'd imagine one is positive and one is negative? Does this receive power while the key is on?

The reason I'm asking is because I do not have a stock ECU or main wiring harness so there is no connector, but I would still like to keep this.

Thanks!
Chris

jrichker · Jan 22, 2009

The red wire is postive with the key on. The gray/yellow is the computer switched ground. The computer provides the ground when the engine is in cruse mode. The solenoid valve opens and vents the gas tank via the line from the intake manifold.

Diagram courtesy of Tmoss & Stang&2birds

1991vert · Jan 22, 2009

jrichker said:
The red wire is postive with the key on. The gray/yellow is the computer switched ground.

so can i ground the GR/Y wire to the body?

jrichker · Jan 22, 2009

1991vert said:
so can i ground the GR/Y wire to the body?

jrichker said:
The computer provides the ground when the engine is in cruse mode. The solenoid valve opens and vents the gas tank via the line from the intake manifold.

This is a controlled process: open the valve at idle and you will probably have idle quality problems.

1991vert · Jan 22, 2009

jrichker said:
This is a controlled process: open the valve at idle and you will probably have idle quality problems.

i have a secondary circuit on my computer for a second fuel pump that switches on when it see a certain TPS %. do you think if i used a 30amp relay and set the circuit to go hot when it sees the throttle blade open about 25% it would work?

jrichker · Jan 23, 2009

1991vert said:
i have a secondary circuit on my computer for a second fuel pump that switches on when it see a certain TPS %. do you think if i used a 30amp relay and set the circuit to go hot when it sees the throttle blade open about 25% it would work?

That sounds good to me, give it a try.

1991vert · Feb 26, 2009

well after going out and looking at the wiring both wires are black...and i dont think it's dirt and grime. what now? how do i know which is which?

HISSIN50 · Feb 26, 2009

If you're talking about your body harness wires at the CANP, turn the key on and put your meter on each wire. One will show constant accessory 12 V (this is VPWR). The other wire is the grounded control pathway.

You could use a SPST relay to switch a ground pulse to the factory control wire.

1991vert said:
well after going out and looking at the wiring both wires are black...and i dont think it's dirt and grime. what now? how do i know which is which?

1991vert · Feb 27, 2009

i do not have a stock main harness...i do however need to hook up the solenoid. all i have is the solenoid itself with the harness coming off of that. both wires are black.

Saleen0679 · Feb 27, 2009

Judging by the schematic it's not going to matter which wire is connected to the power source and which is connected to ground. The solenoid is like a relay in that when current flows through the coil an action happens. With a relay the contacts close and with the CANP the valve opens. The valve itself looks directional though.

Red&black · May 31, 2013

1991vert
Sorry to revive this old thread. I also have a non factory wiring harness for 351 cleveland with aftermarket EFI. I really want to use the emissions purge system. How did you wire the purge valve? THANK YOU

jrichker · May 31, 2013

The computer provides the ground for the solenoid. The red wire to the solenoid is always energized any time the ignition switch is in the run position.

Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber hose. Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve connects to one side of the canister. The other side of the canister connects to a rubber hose that connects to a line that goes all the way back to the gas tank. There is an electrical connector coming from the passenger side injector harness near #1 injector that plugs into the canister solenoid valve. It's purpose is to vent the gas tank. The solenoid valve opens at cruse to provide some extra fuel. The canister is normally mounted on the passenger side frame rail near the smog pump pulley.

It does not weigh but a pound or so and helps richen up the cruse mixture. It draws no HP & keeps the car from smelling like gasoline in a closed garage. So with all these good things and no bad ones, why not hook it up & use it?

The purge valve solenoid connector is a dangling wire that is near the ECT sensor and oil filler on the passenger side rocker cover. The actual solenoid valve is down next to the carbon canister. There is about 12"-16" of wire that runs parallel to the canister vent hose that comes off the bottom side of the upper intake manifold. That hose connects one port of the solenoid valve; the other port connects to the carbon canister.

The purge valve solenoid should be available at your local auto parts store.

Purge valve solenoid:

The carbon canister is normally mounted on the passenger side frame rail near the smog pump pulley.
Carbon Canister:

Red&black · Jun 1, 2013

Big thanks to jrichker for the detailed response. I'm going to hook everything up like outlined. The only difference I see is that the purge valve will be open when the engine is running vs cruise only since I don't have 5.0 wiring or factory computer (351cleveland w/aftermarket EFI). I think this will be ok. I will hook it up and see. I'm not very skilled with electrical systems to know how to make it work for cruise only.

Scrapla347 · Aug 17, 2025

Red&black said:
Big thanks to jrichker for the detailed response. I'm going to hook everything up like outlined. The only difference I see is that the purge valve will be open when the engine is running vs cruise only since I don't have 5.0 wiring or factory computer (351cleveland w/aftermarket EFI). I think this will be ok. I will hook it up and see. I'm not very skilled with electrical systems to know how to make it work for cruise only.

Are you still around and if so what did you end up doing with this? I just took out my factory wire harness to install a Terminator X. My charcoal cannister solenoid isn't connected to anything so I was going to remove it and leave the cannister to help catch any fumes.

AeroCoupe · Aug 17, 2025

Last seen June 1, 2013.

Scrapla347 · Aug 17, 2025

AeroCoupe said:
Last seen June 1, 2013.

RIP

Scrapla347 · Aug 17, 2025

I modified my charcoal cannister but don't feel like rigging in a wire to keep the solenoid working. I disconnected it years ago but left it on the cannister and just had the wire tucked away.

5ptslow · Aug 19, 2025

Scrapla347 said:
I modified my charcoal cannister but don't feel like rigging in a wire to keep the solenoid working. I disconnected it years ago but left it on the cannister and just had the wire tucked away.

So i could just bolt the canister up in rear bumper and run the tank vent to it and out the canister to open air?

General karthief · Aug 20, 2025

The charcoal canister works on vacuum so no vacuum, no worky right. There is a vent system I've seen in the Hagerty mag, I'll see if I can find it, meanwhile remember, our cars have a closed system, so you don't want constant vacuum to the charcoal canister, unmetered air is an issue.

Scrapla347 · Aug 20, 2025

My cannister wasn't hooked up for years. I left it in the engine bay but the vacuum line and solenoid were all disconnected. I got it tuned like that. Now it's Terminator X time.

Canister Purge Solenoid

1991vert

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lube between the nut and the face. I know my lubes

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wonder how much it would cost to ship you a pair

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lube between the nut and the face. I know my lubes

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wonder how much it would cost to ship you a pair

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