buckgrunter

The purge solenoid is normally closed...I assume that's correct. When 12v is applied to the solenoid, it opens. I'll retest at a deeper vacuum and compare to the intake manifold. I just don't understand that if I am >154F and >0mph that the solenoid doesn't open.

Former User

I agree.

Again, the valve has constant voltage with key in ON(II). It opens when the ECU supplies ground.

Based on your vacuum measurements, the question is not "why doesn't it open" but rather "why doesn't it close", right?

buckgrunter

Not sure I follow. Solenoid is normally closed and results in test vacuum (in #3 and #4 tests). The 12v test I refer to is with the purge solenoid removed from the vehicle. I apply 12v with ground, the solenoid opens. I think my vacuum measurements indicate that the solenoid is not opening (or ground is not being applied through red/yel)?

Former User

When the purge solenoid is closed, you should not measure any IM/engine vacuum at the cannister hose.

See second diagram in post #23. Think about how the evap system works. It uses IM vacuum to suck fuel vapor from the canister into the cylinders. The purge solenoid controls whether vacuum from the IM is allowed to suck fuel vapor out of the canister. In the first 3K rpm test, you should not measure vacuum because the purge solenoid should be closed, right?

buckgrunter

When I test the solenoid at ambient conditions (solenoid closed) I measure vacuum. I would think that I should measure vacuum at the canister hose because I'm testing from the canister side and the solenoid valve is closed? I'm lost... I need another beer!

Former User

See second diagram in post #23.

Here's the configuration of the relevant components:
Cannister --> purge solenoid valve --> IM

Arrows point in direction of fuel vapor flow when solenoid is OPEN.

You are looking for vacuum at the cannister when the valve should be closed. Since vacuum is generated at the IM, you should not measure vacuum at the cannister when the purge valve is closed. Make sense?

buckgrunter

I get everything but the last comment. "You should not measure vacuum at the canister when the purge valve is closed". To clarify, the purge valve you refer to is the purge solenoid? The solenoid is electrically operated and not pneumatically. I still am thinking the purge solenoid needs a ground signal to open so fuel vapor can flow to the intake?

Former User

The source of vacuum is the IM. If the purge solenoid valve is closed, why would you measure vacuum at the cannister? Make sense?

The purge solenoid needs a ground signal to open. With the valve open, then vacuum from the IM can reach the cannister. Make sense?

Think of the IM as a vacuum cleaner.

buckgrunter

Not really. If the purge solenoid is closed I measure vacuum at the canister, right? When a ground is applied the solenoid opens to the IM.

Former User

But you should not measure vacuum because the closed solenoid will block vacuum from reaching the cannister. The solenoid is acting like a closed gate that won't let vacuum pass to the cannister.

Correct. And when the solenoid is open, you should measure vacuum at the cannister.

buckgrunter

If the purge solenoid is closed and I test the vacuum line from the solenoid valve (vacuum pump at the disconnected canister vacuum hose) I should I test vacuum. Right? At idle, I get vacuum. At 3000rpm+, I get vacuum. Doesn't that mean the solenoid is closed or equate to test vacuum at the canister vacuum hose? Thanks for putting up with me.

Former User

Since the engine is cold and the A/C is off, the valve should be closed and there should be no vacuum. Since you are measuring vacuum when you shouldn't, the valve is open when it should be closed.

Former User

The first two tests with the vacuum pump tested the vent shut valve.

The later tests without the vacuum pump tested the purge valve, which is what we are currently discussing.

buckgrunter

With the valve removed from the car, the valve is closed (I cannot blow air through it). When I test the valve, removed from the car, with 12v and ground, I can blow through it. That means the valve is normally closed and I should get test vacuum at the canister (in test #3) when the valve is installed and hooked up to the IM?

buckgrunter

That's it! Vacuum gauge, not a vacuum pump. I'm finally coming around....

Former User

This^ is where you are coming to the wrong conclusion.

With the engine cold and the A/C off, the valve should remain closed in test #3, thereby preventing vacuum from the IM from reaching the cannister. The fact that you read vacuum in test #3 indicates the valve is open when it shouldn't be or that the vacuum hose is improperly routed, as mentioned in the service manual.

Former User

Are we on the same page now?

Former User

The hose you are attaching the vacuum gauge to in tests #3 and #4 should lead to the purge valve in question.

buckgrunter

Yes! I never saw the vacuum pump vs. vacuum gauge. I'll test and report back. Still not sure why 20 inHg would skew the results of an electric purge solenoid, but I'll retest.


I appreciate all the help. Do you take beer or cheese as payment?

Former User

I recommended the deep vacuum for prolonged times before I realized that the troubleshooting is pointing to a stuck open purge valve. Focus on the latter now.

Former User

This diagram may be helpful to you:

buckgrunter

Last question before retesting. Stuck open purge valve would mean it won't open with electrical ground, right? Both purge valves I have open with 12v applied and a ground.

Former User

Based on your test results, if done correctly, the purge valve is stuck open when installed in the car. In test #4, you unplugged the purge valve and it still remained open (vacuum detected), so it's open even without power or ground. For some reason, removing the valve from the car makes it function properly. Nonetheless, you should now try to figure out why the valve is open when installed.

buckgrunter

Solved. The red/yel wire between the purge solenoid and A15 was open. Soldered in a new wire and good to go. Thanks Ron for walking me through this!

Former User

Nice job.

Must have been open and shorted to keep the valve open?