EVAP leak hard to find

Tiny
CHEVYOWNER10
  • MEMBER
  • 2010 CHEVROLET AVEO
  • 1.6L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 76,000 MILES
Let me discuss what's going on with it. I think there might be a hard-to-find EVAP leak present. The strange part is that the vehicle is running fine now, but before it wasn't. When you have time, please read this, and let me know what you think.

It all started when I was in the gas station refilling the tank. After getting gas I started the vehicle and the rpm needle was acting crazy. The car was having trouble staying running. I had to slam on the gas to keep it running and idle got better. Two days after my check engine light comes on when I start the vehicle in the morning. Code P0496- evap emission system high purge flow was present. I checked the vapor canister purge valve solenoid for any vacuum present. The old valve was holding vacuum in it. I replaced it and erase code. Check engine light didn't come back ever since. The vehicle idles fine at the time the code set.

Now here's where it gets strange, today I drive the vehicle and it was fine the entire time I was out. But at the end of the day when I was on my way home the rpm needle decided to act strange again. I pull in my driveway and the engine starts to misfire like crazy with the rpm needle freaking out. I shut off the ignition, went out and smelled a rotten egg odor from the tail pipe. I start the vehicle again and engine is still misfiring. I drive out of the driveway and the car stalls. It stalled out 3 times on me while driving it.

I parked in a spot and let the car sit. I went back out to check it out 15 mins later and the idle is smooth again. There was no more misfiring. I was able to drive it without it stalling out on me. I connect a scanner to it and found out there were two codes that read P0496. One was stored in the pcm from before when the light first came on in the first place and the other came back pending. No check engine light was on. But the code was still there. I checked fuel trim levels, short term, and long term. I notice fuel trim levels were rich and kept climbing than moving back to lean. It would run richer with the ac running on long term trims. I also notice one of the on-board monitors under flow monitor of the purge solenoid status was at fail. None of the monitor values were at fail before when I replaced the sensor.

All over YouTube this code say's it's very common that it's the purge solenoid. If it's stuck open there will be vacuum present. My tests conclude vacuum was present in the valve. So, I replaced the part and was fine until now. I have been having the rpm needle act weird on me ever since last year. Sometimes the engine would surge when the rpm needle went crazy. But it never stalled out. I don't know if it's a bad fuel tank pressure sensor or bad vacuum leak.

I don't have an evap smoke tester kit to trace the leak or any scanner that can tell me what the ftp sensor is reading. It's not easy to access because it's on top of the tank. I would appreciate your time getting back to me.
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Friday, March 18th, 2022 AT 9:35 PM

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Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,235 POSTS
I have seen the EVAP vapor canister cause a leak and also allow raw gas to enter the engine at particular times, what you have described sounds like this issue. To confirm this issue when the engine is running badly remove the vacuum line that supplies vacuum to the EVAP system and see if there is gas in it, there should never be gas in this vacuum line. I have included EVAP canister replacement instructions in the diagrams below. Check out the diagrams (below). Let us know what happens and please upload pictures or videos of the problem.
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Saturday, March 19th, 2022 AT 6:06 PM

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