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canister purge valve revisited


Explorer Addict
December 27, 2001
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City, State
Spanish Fork, UT
Year, Model & Trim Level
92 XLT and '87 Bronco II
Been having the occasional gas smell from my Explorer. Dropped the tank this morning to make sure that there were no gas leaks on top of the tank. That's when I found the vapor line that runs to the charcoal canister. I remembered that this system can sometimes create gas smells. Verified that there were no gas leaks to speak of, and turned my attention to the evaporative emissions system.
Found several discussions on this:part numbers for '94. The Ford part number given here doesn't match the one on my solenoid, and my solenoid is down near the cannister where it's easy to get to.
a fairly lengthy discussion spanning several model years
Anyway, has anyone ever played with diagnosing the electrical controls for the purge valve? Here's what I've done.
Using a hand vacuum pump, checked the vapor lines, and they are all free and clear.
In the output state test mode, the canister purge solenoid never opens. This was shown by both the vacuum gauge on the intake side of the valve, and the voltage drop across the PCM would cycle between 11.7 V and 12.5 V. I would have expected it to cycle between 0 and 12 V, but the circuit test from the manual says that 0.5 V change is adequate. The resistance of the solenoid was about 60 ohms, right in the 40-90 ohms the circuit test suggested it should be. If I manually ground the solenoid, it opens cleanly, but, of course, is no longer under PCM control.

Part of me wants to blame the solenoid, the other part wants to blame the PCM itself. I know PCM's don't fail very often. Because it was suggested that the solenoid isn't very expensive, I thought I might change that first, but Autozone wants $53 for the part that mathces the Ford part number stamped into the solenoid, and Napa closed too early. (My one complaint against Napa, they're never open when I, a backyard mechanic, need them to be, but that's another discussion).

For now, I think I'll take a cue from my BII, and leave the solenoid grounded so it's always open. The EVAP system in my BII doesn't even have a valve; it's open all the time and purges whenever the engine's running. Probably works better on the speed density system than it will on the mass air system. Question. Has anyone had their solenoid stick open that can comment on the problems this might cause? In the short time I've run it, it doesn't seem to effect how the engine runs. I also intend to work out the problem more permanently when Napa opens and I can find out about getting another part.

The big question, though. Has anyone played around with the electronics that can comment on the electronic symptoms?

Sorry this is so long. Thanks for reading, and thanks in advance for any help anyone can lend.

Bill Kemp

Elite Moderator Emeritus
Moderator Emeritus
April 2, 2000
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City, State
Greenville, MI
Year, Model & Trim Level
98 Mountaineer 5.0 AWD
I looked ay my Haynes manual to framilerize myself with the canister ect. and they say that on 94 & earlier Xs there are no moving parts in the EVAP system. If the hoses ar not loose, cracked...& the canister is OK than the systems OK.
"The vapor is vented through a valve in the top of the gas tank and routed to the canister where it is stored untill the engine is running."
Now you know all I know.....