LE9 305 ESC backfires through exhaust on deceleration

[Turbo4whl]

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[ChuckN]

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What I see when I look at emissions diagrams. Sorry, I know that’s not helpful.

 

[Turbo4whl]

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What I see when I look at emissions diagrams. Sorry, I know that’s not helpful.

Here, I'll make it easy for you.

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[SirRobyn0]

Poor little 305 gets a bad wrap by many of the members here on this forum. Why, well it has 45 less cubic inches than it's bigger brother, the 350.

What is this engine? It's an air pump. Bigger is better right? Well maybe not if you are trying for fuel economy and cleaner emissions. The historic Small Block Chevy, born in the 1950's at 265 CI, quickly up to 283 CI and powered big heavy vehicles.

So maybe now I have you thinking... what happens when you decel? Throttle closes, engine vacuum jumps up. What is the engine again? Big air pump. So this high vacuum draws air back from the exhaust.. Backfire!

GM knew this, added a decel valve. Your 305 had one. Is it there? Is it working?

I quite agree. My 305 has done everything I've ever asked it to, I think and this is just my personal opinion but I think that the 305 gets a bad rap because people try to treat it like a 350 and it's not. And what I mean by that is like tuning wise trying to treat them the same and that doesn't work. Pulling all the emissions stuff off a 350 works fine but pulling it off a 305 does not for example. It's just a different engine but treated correctly it's not to bad.

 

[TDoc]

Exhaust is stinky with air pump hooked up or not. Not that I love huffing exhaust fumes but this k5 has a distinct smelly exhaust. I put dual 2.25” exhaust on it and it has a little more power vs when it had the crunched y pipe stock exhaust.

Can I just leave air pump disconnected and everything hooked up as it was?

 

[SirRobyn0]

Exhaust is stinky with air pump hooked up or not. Not that I love huffing exhaust fumes but this k5 has a distinct smelly exhaust. I put dual 2.25” exhaust on it and it has a little more power vs when it had the crunched y pipe stock exhaust.

Can I just leave air pump disconnected and everything hooked up as it was?

Dual cats. You can get high flow cats if your concerned about the added restriction.
Having a working air pump will help the cats to "light up" aka start working quicker and keep them from dropping out during long periods of idling. It's all up to you but I can tell you that my 84' 305 with dual exhaust, dual cats and functional air pump does not have smelly exhaust at all. I actually have some lung issues and driving my truck without cats would have me pumping on my inhaler afterwards.