Hoping for some EVAP smoke test tips-GA 2001 6cyl [Archive] - GrandAmGT.com Forum


View Full Version : Hoping for some EVAP smoke test tips-GA 2001 6cyl

04-30-2012, 02:32 PM
Hey folks,

Glad I found this forum. It's pretty impressive compared to some others I've been browsing to find some tips.

I'm throwing a Small EVAP Leak code p0442. Gas cap is somewhat new, and I'm going to run a smoke test. I had a few questions about doing so I'm hoping you can clarify.

I made my own smoke machine that I tested and it works pretty well. I don't have a schrader valve on the end to feed into the green test port, so I'm just going to unplug the hose where it connects to the purge valve and feed it back and then feed it forward (basically do one test one way-toward the charcoal canister, then one test the other way-through the purge valve and into the intake.

So, I guess I'll just list the questions, though I know answering a list is never fun.

1. I was wondering how to open the solenoid when the car is off, since it is closed from what I hear until the car is on for a while (smoke test has to be done with car off). I heard some things about attaching the electrical leads of the valve to the battery, but I'm getting mixed info about this.

2. Some sources mention a vent solenoid by the gas tank and the charcoal canister. Not sure if there is one there on this model car, as I'm getting mixed info about this too. If there is one, how do I open this to let the smoke through? By the way, I don't have one of the expensive scanners that can tell these valves to open.

3. I've heard I should remove the gas cap to make the smoke go through the system better. Thoughts?

4. I haven't seen a Factory Service Manual for this car and don't really want to buy one, but I do have the Haynes manual, which seems to get many details wrong (surprised? Heh). If anyone does have one, care to post the section on evap or relevant scans or a PDF? I'm not sure if this is against forum rules, but if so, I apologize and please disregard. Basically hoping for a real evap system diagram for this car that doesn't look super-generic as if made for any old car like most evap diagrams I find online.

5. Do I have to keep the throttle pulled down on this model when doing the smoke test into the manifold?

Thanks so much, folks. I really appreciate it!


05-01-2012, 06:04 PM
For starters you don't want to have anything open to atmosphere when you're performing a smoke test. You wouldn't build up any pressure in the EVAP system and the smoke wouldn't show where your leak is.

The purge solenoid is normally closed so that's okay as long as you can't blow air through it from either direction.

The vent valve is normally open but you want to close it for this test. To do this you need to look for a connector on the passenger side just in front of the fuel tank. There'll be a cluster of three connectors. You're looking for the white connector with four cavities and two wires going into it. The wires will be white and brown.

If you unplug that connector and apply power to the brown wire and ground to the white wire, you should hear a click. That'll tell you the vent valve is operating properly. If you don't really hear a click then the vent valve may be the source of your leak.

Don't worry about the throttle. You can test the evap purge solenoid independently by applying smoke to either end or trying to blow through it. If you can blow through it, the solenoid is bad.

Hope this helps you.

05-02-2012, 10:18 AM
It's interesting you mention the vent valve is normally open, as all other resources I found said both the purge and vent solenoids are closed until the PCM determines it's ok to open both. So, I guess I'm a bit confused by what you said there.

Since the purge solenoid goes through another hose to the PCV valve, I kind of wanted to know how to open that too in case the leak is at the valve or on that hose. Would the manifold have enough pressure to show smoke escaping here?

So what you were saying about how nothing should be open, this was in reference to the gas cap question?

Thanks again!


05-02-2012, 07:07 PM
The vent valve is normally open so you can fill the tank. Since the Purge valve is normally closed, a filling pump would kick back when trying to fill. So the vent valve allows a path for the displaced air from the fuel tank to pass through the charcoal canister to catch fuel vapors. Then it exits via the vent valve.

When the engine is running and certain conditions are met, the vent valve is closed and the purge solenoid commanded on to draw fuel vapors from the canister into the engine to be burned.

The PCV valve has nothing to do with the EVAP system. You can actually unhook the purge solenoid and test it independently of the rest of the system. So basically unhook both hoses from the purge solenoid and see if it'll hold a vacuum from either direction. Basically suck on the fitting on each side. If you can draw air through the valve it needs to be replaced.

And yes the gas cap should be left in place during a smoke test to pressurize the system.

05-03-2012, 09:47 AM
So there's really no need to smoke test from the purge valve to the PCV valve, and therefore, to the manifold? I only need to smoke test toward the rear to fix an evap leak? I mean, other than testing if the purge valve works, of course. Basically, P0442 would only be thrown from the purge solenoid back?

Could I also test the purge valve (see if it switches) using the same electrical test as the vent valve?

Thanks again! Your explanation makes lots of sense.


05-03-2012, 07:28 PM
Correct. No need to smoke test beyond the purge valve. EVAP codes start at the purge valve and end at the gas cap/vent valve.

You can test the purge solenoid in the same way I mentioned closing the vent solenoid.

05-04-2012, 09:33 AM
Thanks! I really appreciate you clearing that up. I guess this video kind of led me to believe otherwise:


Not a Grand Am, of course, but evap systems don't seem to differ all that much between cars, it seems.

He smoked the system in both directions and mentions the throttle plate. Since he is doing an evap test, any idea what his motives were?

Will be attempting the test tonight. Thanks again!