Engine Backfire

apex96

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More then likely fuel has puddled up in the cylinder and when you restart a hot vehicle that extra fuel gets pull through without being combusted. The exhaust is still hot and once the fuel hits the exhaust it ends up igniting.
 
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blue_roster_cult

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More then likely fuel has puddled up in the cylinder and when you restart a hot vehicle that extra fuel gets pull through without being combusted. The exhaust is still hot and once the fuel hits the exhaust it ends up igniting.
No… It ONLY happens after refuel. I can drive all day, go to the store, go to eat, go anywhere, and then if I stop for gas and fill up, it backfires. An issue shared by many per the 4 threads I posted. It’s not a tuning issue.
 

rd618

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No… It ONLY happens after refuel. I can drive all day, go to the store, go to eat, go anywhere, and then if I stop for gas and fill up, it backfires. An issue shared by many per the 4 threads I posted. It’s not a tuning issue.
More than likely it’s evap system related due to your lack of sensor readings. Like others posted it’s running rich. When you fill the evap and emissions systems reset slightly when you add more fuel. It’s based on how much fuel fills the tank and how much you had before. In simple terms they monitor the amount of gas that evaporates and how much of a vacuum you hold.
If you want to test this. Drive down to 1/4 tank. Then put half to 1 gallon in. Re start. Nothing will likely happen. Put in more and you will notice the same behavior you have now.
 

LokiWolf

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Let's sum up.

You called it a "Common" issue, it isn't. PERIOD.

You have been given 2 things that could be causing it, O2 Sensors being disabled because of no Cats, and the EVAP system. In reality, it is most likely a combination like was mentioned above. Hot Exhaust, Rich condition, Nocats, and EVAP system not working at 100%. If you are running without cats, and the sensors are turned off with out any other adjustments, it will make the issue worse, because the systems is defaulting to rich.

Get a proper tune for no Cats(Which the best tuners out there won't touch with a 10ft pole), or put cats back on and turn sensors back on. Also looks like maybe inspecting the EVAP system and make sure everything is working as good as it can? You asked for help, we are offering it. You want this to be unrelated to what you have done, but it most likely isn't.
 

purevw

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No… It ONLY happens after refuel. I can drive all day, go to the store, go to eat, go anywhere, and then if I stop for gas and fill up, it backfires. An issue shared by many per the 4 threads I posted. It’s not a tuning issue.
It takes 5 minutes to refuel. The store, eating, etc., usually take longer than that. Timewise, they are not comparable.
 
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blue_roster_cult

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For anyone interested, here is what the backfire did to the muffler. It blew this baffle (which should be square with the cut lines) out of place. This definitely did not result in a performance upgrade.
 

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