Novak Conversions Jeep Wrangler TJ radiator

Purge Valve Solenoid Behavior

SSTJ

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Context:
  • I'm troubleshooting MIL code 31 (P0441), which I posted about over here.
  • This post led me to believe that my purge valve solenoid needed to be replaced, as mentioned here.
  • Now I'm not so sure. Reasons given below.

My Understanding:
  • The purge valve solenoid has two ports, each with a hose attached. One hose goes to a port on the intake manifold, and one hose goes to a port on the charcoal canister.
  • The purge valve solenoid is "de-energized" until the TJ reaches operating temperature. During that time the TJ is in "open loop". At this time the purge-valve solenoid does not purge any vapors from the charcoal canister to the intake manifold.
  • When the TJ reaches operating temperature, and is in "closed loop" operation, the purge valve solenoid will "pulse" anywhere from 5–10 times per second. This pulsing is what purges vapors from the charcoal canister and sends them to the intake manifold.
  • Am I right so far?

My Questions:
  • 1) Let's say I cold-start my TJ and immediately disconnect the purge-valve solenoid from the charcoal canister. One end of the hose is in my hand, and the other is still connected to the purge valve solenoid. I feel and hear a gentle, consistent suction in this hose. It's not very strong—in fact, if I reconnect that hose to the charcoal canister, and then remove the other hose from the other port on the charcoal canister, I cannot feel the same suction on that port. Is this gentle, constant suction normal while the TJ is in open loop operation? Is this just the vacuum pressure from the intake manifold, passing through the purge-valve solenoid?
    • Answer: No, when the purge valve is closed (de-energized), no air should be passing through it. Especially if you unplug the purge valve's electrical connection, which would ensure that it is de-energized. In either case, you should not feel the intake manifold's vacuum pressure passing through the purge valve. See the first video posted here.

  • 2) Let's say I let my TJ warm up to operating temperature, and now I disconnect the purge-valve solenoid from the charcoal canister. Again, one end of the hose is in my hand, and the other is still connected to the purge valve solenoid. What should I feel? How strong is this "pulsing" that it does? How long should I wait to feel it? When I try this, I only feel the same gentle, constant pressure that I feel described above.
    • Answer: The vacuum pressure you should feel is just that same gentle pressure described above. However it should not be constant. You should feel and hear the purge valve pulsing, but that pulsing is just an opening and closing, so the pressure you feel during those pulses is no greater than the intake manifold vacuum pressure itself. See the second video posted here.
 
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My understanding of operation matches what you wrote.

The manifold should be around 15 inHg I believe. When I put my finger over the opened purge valve there was suction but it wasn't particularly strong. It could leave a little dimple on my finger. I didn't feel any pulsing, only constant vacuum.

Do you have a Mityvac? If so you could connect it to the system and see what it is. Also the DRBIII will tell you what the manifold vacuum is.

I just went through this with P0441 and I did a test where I confirmed the purge valve was working by looking for no vacuum and vacuum, however the next day I filled the tank and the Jeep was hard starting. That is a symptom of a purge valve that is stuck open, so I just replaced it today. I used the Standard Parts version from RockAuto - $30 as I have had good luck with Standard Parts in the past.

I suspect my P0441 was being caused by the rubber hose that goes from the tank to the filler neck. It's a hodge-podge of tubes and hose clamps and looks home made. I think the check valve inside the tank was not fully closing allowing vapours to travel up the filler neck and leak out before reaching the brand new gas cap. Now that I have done the check valve fix I hope it is solved. If not I will do a smoke test next.

Andy
 
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The manifold should be around 15 in Hg I believe. When I put my finger over the opened purge valve there was suction but it wasn't particularly strong. It could leave a little dimple on my finger. I didn't feel any pulsing, only constant vacuum.

Exactly. Thanks for confirming.

Do you have a Mityvac? If so you could connect it to the system and see what it is. Also the DRBIII will tell you what the manifold vacuum is.

Interesting. Unfortunately I have neither.

I just went through this with P0441 and I did a test where I confirmed the purge valve was working by looking for no vacuum and vacuum

Can you say more about this? As mentioned in my post, I get that gentle, constant vacuum at all times, it seems.
 
My understanding of operation matches what you wrote.

The manifold should be around 15 in Hg I believe. When I put my finger over the opened purge valve there was suction but it wasn't particularly strong. It could leave a little dimple on my finger. I didn't feel any pulsing, only constant vacuum.

Do you have a Mityvac? If so you could connect it to the system and see what it is. Also the DRBIII will tell you what the manifold vacuum is.

I just went through this with P0441 and I did a test where I confirmed the purge valve was working by looking for no vacuum and vacuum, however the next day I filled the tank and the Jeep was hard starting. That is a symptom of a purge valve that is stuck open, so I just replaced it today. I used the Standard Parts version from RockAuto - $30 as I have had good luck with Standard Parts in the past.

I suspect my P0441 was being caused by the rubber hose that goes from the tank to the filler neck. It's a hodge-podge of tubes and hose clamps and looks home made. I think the check valve inside the tank was not fully closing allowing vapours to travel up the filler neck and leak out before reaching the brand new gas cap. Now that I have done the check valve fix I hope it is solved. If not I will do a smoke test next.

Andy

Also, do you have any insight on my question #2?
 
Also, do you have any insight on my question #2?

You should feel the manifold vacuum through the valve as it opens. I don't know if our vehicles are supposed to pulse or not or if the lack of pulse means something. I didn't have pulsing.

These are the two videos I looked at:



Andy
 
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You should feel the manifold vacuum through the valve as it opens. I don't know if our vehicles are supposed to pulse or not or if the lack of pulse means something. I didn't have pulsing.

These are the two videos I looked at:



Andy

Thanks, very helpful. I updated my original post with your answers, in case anyone else comes across this thread.

Everything I reported in my original post was true after putting in a new purge valve, and so I may need to return it and try another one.
 
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Novak Conversions Jeep Wrangler TJ radiator