Thanks although I'm starting to think my issue is something different. Pulled the electrical connector for the purge solenoid and my afrs were stable. Plugged the solenoid with vac cap and still have weird afr fluctuations.

 

I'm having P0455 and Check Gas Cap on the DIC. I replaced the gas cap and the canister solenoid, so the one on the engine is the last thing I'm going to try. For anyone looking for this part, I found a guy with a few on ebay for $10 shipped. Left over stock from a plant closing.

GM 12608378 Vapor Canister Purge Valve, New | eBay

 

Finally got around to it guys, but is this signs of needing a new solenoid


Sporadic AFRs - YouTube

 

You can always unplug the solenoid to find out. If your afr stabilizes after its disconnected its your solenoid

 

Judging by the amount of vac you have at idle, I'd say you have a vac leak somewhere. I'm not sure where, though.

 

No that's Colorado norm. We never get below or at -20

But it does bounce so maybe you're right.

***Edit*** I think my problem is something other than Evap

I made a thread about it so I don't clog up this one.

 

Today CEL came on. Codes P0496 and P0497.

Found this thread. Thanks for all the help guys. I checked my purge solenoid and it is bad. To see how to test whether yours is good or bad there's a video of it on Youtube. They're showing it on a Solstice but you can easily tell how to do it on a Cobalt. Here's the link:

DDMWorks - EVAP Solenoid Testing and Replacement on Ecotec engines - YouTube

The guy on Ebay still has them for 9.90 shipped. I went ahead and bought two.
He has them listed as the old part number 12608378. The part number on the one on my car is 12592015. They are the same part.

Also, here's the link for the ones on eBay:

GM 12608378 Vapor Canister Purge Valve, New | eBay

 

i've replaced that damn thing 3 times in mine already

 

Subbed

 

car freaked out over the weekend

STFT and LTFT all over the place and rough start after gas fill up.

This is the 3rd one to go on the car.

Enjoy

LNF Evap Purge Selenoid - YouTube

 

What are the symptoms of the canister going bad in the rear of the car? I get random rich spikes sometimes and when I start my car the vac sits on 10-15 for a few seconds and the car runs wierd. After those 5 or so seconds the vac jumps to 20 and all is normal.

 

There's also a purge valve back there you might want to check.

 

Not sure about the canister, but the vacuum can change or appear to change when the car is in open loop and enters closed loop once the O2 sensor is ready/warm. The O2 sensor is used by this ECU in part to calculate airflow from what I've seen.

If you've got more than one gauge, stick one on AFR and the other on vacuum/boost. The car will warm up, and then once the O2 sensor comes alive and starts reading, the vacuum reading will change. This is especially noticeable after a fresh tune flash, where the car hasn't had a chance to adjust to the fuel trims for the first time or anything yet.

Yeah, that's the "evap vent valve". From what I read, it's supposed to always stay open unless it's being closed by the ECU for an evap system diagnostic.

 

I'm not sure if we have ever determined symptoms for each part.

I had random rich, random lean and everything in between when my Evap purge selenoid went bad.

Also had weird idling and backfiring.

 

Yeah, I don't think we did either. I've been having the random rich/lean thing start up again recently. I put in a new replacement Purge Solenoid and it's still doing it. I'm wondering now if it was the Vent Valve instead.

I pulled out the vent valve and it doesn't appear mechanically stuck or anything. My only thought on that is that there's something electrical going on with it. Due to a spring in it, its failure mode should be open/venting.


A recent theory of mine:

Another thing I've been wondering about recently is the design/use of the Purge Solenoid itself. As stated way earlier in this thread, a GM engineer stated that they had field issues with this solenoid. I'm wondering if they took this one off of a naturally aspirated car and decided to use it on this engine. If you look at where the check valve in the line is, it's "above" where the solenoid is. After checking a known good solenoid, I was able to verify that although the solenoid doesn't allow flow until told to do so by the ECU, it does allow backflow. Therefore, I'm wondering two things:

-Boost pressure in the IM could be damaging this valve, especially when it's getting suddenly slammed by a [back]pressure spike, and more so when it's higher boost pressure than stock.
-The valve could be trapping boost pressure in the line between the solenoid and the check valve, and therefore releasing far more pressure than normal when it is opened again. This would cause that exaggerated AFR swing we've been seeing.

Therefore I'm thinking that it may be beneficial to move/add a check valve to between the Purge Solenoid and IM, so the solenoid never sees boost pressure.

 

Has anyone cut a purge valve open to see what's inside?

I have no idea how it works and would like to know.

Is it something that's getting gummed up or loses viscocity and sticks open. Is it something that is physically breaking open.

Anyone have ideas? Seems like someone could come up with a better solution.

 

I like your theory and I am very interested in the bolded text. I hope that this is possible.

 

I didn't want to let the cat out of the bag just yet until I had data that seemed promising, but since we're on that specific topic...

I've got a corporate sample from a valve company being shipped out to me that I'm going to use with 07BoostedG5 (/88 Fabrication Studio) to fab up a prototype solenoid for testing. We'll have to see after that how promising that modified solenoid is and determine:

-Whether or not the solenoid is getting damaged due to being used in a boosted application or through tunes with raised/quicker boost levels
-How promising better flow control is for dampening AFR spikes
-In general, if the classic evap driveability/AFR symptoms disappear with better evap flow control

The valve will be Ethanol resistant, and the seal will incorporate Viton to further ensure long life around Ethanol, for people that prefer that fuel.

 

Alright, so i disconnected the line on the EVAP solenoid but left the electrical connector plugged in and capped off the solenoid (the one on the intake mani)

took it for a spin around the block, didnt go into boost. AFR seems the same (never had an issue with it in the first place)

but my fuel trims are WAY better. LTFT stays close to 0. i saw it bounce up to 7 only once, but it stays from 0-4.

stft's dont bounce around like crazy either. they used to bounce around like crazy (jump to like -10, then go to +15, then go back to normal) and now they are way better.

before, at idle, my LTFT's were around 10 and my stft's were always like -5.

at light throttle, ltft's would go to 5.6, and when coasting they would go to 7.9. then right back to 10 at idle. lol

 

my car idles funny most of the time will swing rich then lean and itl wanna die put come back.. unplug the solinoid? im a 2.2 turbo

 

^^You might have other issues. Have done a leak test?

 

id try this first, since it only takes like 5 minutes.

just make sure you reset the ecu (disconnect the battery) first. i think it could be evap related since the same thing was happening to the OP. apparently his issue was the vent valve on the canister, but bypassing the EVAP system all together like i just did may work.

if it doesnt solve your issue, then something else is up.

 

I got a P0455 and check gas cap tonight.. cleared the code and it went away.. however, I wonder; does this mean the evap solenoid is gone or on it's way out? How do I know if it's the one on the intake mani, or the one on the rear of the car though? I'll take a look at the one on the IM either tomorrow or the next day and see if I can blow through it or not. Car has been jerky at light throttle for almost a year now.. I kinda suspect it's this stupid solenoid thing.. has anybody found a way to get around this gay system safely and completely?

 

I was trying to remember if very many people have had the vent valve go bad. Most of us have had the purge selenoid go bad. I would start by testing that because it's easy.

 

should be at the back of the car by the TWB the black box - there.