Purge Control Soleniod Valve mystery

[skibumm100]

I've been tying to troubleshoot my Check Engine Light situation. I'm getting a code PO443, Evap Purge Control Valve. So far I've unplugged the valve and checked for 12 VDC at the plug, KOEO. I got it...every time. I've checked resisitance on the valve....27.5 ohms. Between 10 and 100 ohms is OK. I've taken the valve off and jumpered it across a 12 VDC source, the battery terminals, and it clicks every time. Today I pushed a couple of straight pins through the insulation on the wires at the plug and checked across the pins with the valve disconnected, 12 VDC, same as at the plug connections. I plugged the connector onto the valve and I get 0.6 VDC when checking the pins. It looks like the voltage sourcing the solenoid valve is being pulled down by the load of the valve.....but the resistance is in spec.....and the valve works fine when fed a hot 12 VDC. I don't have a detailed schematic showing where the wiring for the plug is fed from. Has anybody had this problem before? Can anyone tell me where this little gem is fed from? Wiring colors, etc? Thanks for any help you can offer.

[skibumm100]

update:

 

I did a couple of more checks. I disconnected the valve and put a 12 V test light across the terminals of the plug and checked voltage to ground. While feeding the test light, I still had 12.1 VDC to ground, same as with no load. I think the 12 VDC source is good. I checked resistance to ground on the negative lead of the plug. I got 14,200 ohms to ground. I think that's why it won't work. Whatever the negative lead goes through has too much resistance. Reading across the plug w/o the valve connected is like an open circuit because a voltmeter has infinite resistance, therefore there is no current in the loop and no voltage drop across the resisitance. Once I connect the plug, I no longer have an open circuit and the high resistance in the circuit consumes all the voltage and the current goes low. There is no voltage left to power the valve because it gets consumed by the high resistance elsewhere in the circuit. Question is....where's that high resistance? ECM? Is there a relay somewhere that this goes through with bad contacts? Anybody know???

[Cougar]

You are correct about the source wire having a problem. My info shows a wht/blu wire going to pin 72 on the ECU ties to the valve.

 

EDIT

 

I just read your second post. Looking at my info again it appears we are looking at the circuit backwards. The ECU provides the ground side of the circuit, not the power. The power comes from the main relay, which is behind the left side of the dash, on a yel/red wire. Power to the relay comes from SBF-2 on a red wire to the relay. The yel/red wire also goes to a lot of other places.

[skibumm100]

Cougar,

 

Thanks for the reply. Does pinn 72 on the ECU provide the ground or the voltage supply? I think my power side is good. I need to trace the ground side of the circuit. If I can find out where it goes, I'll check way downstream (at the ECU maybe?) and see if the resistance is still really high. If it isn't high, I should just need to pull new wiring. If it's corrosion or a bad plug, I might be able to fix that. If it's inside the ECU.....well....I don't really want to dig into it unless I have a spare.

[Cougar]

The ECU provides the ground internally for the circuit. Check the voltage at the ECU pin and if it is more than .5 volts the problem is inside the ECU.