RPM Motor Sports offer tunes for the 2.4L LE5 $399
Easy to communicate with them.

Look at there Stage 2 kit.
It includes New Larger GM injectors.

Silverfox

 

EFI and VVT make backfire nearly impossible.

Does your car have the "spark pack" or the individual coils? If it has a spark pack that would for sure indicate a leaking injector. That system fires 2 cylinders each time, so one would be on the exhaust stroke and one on the intake etc.

 

I will check it out. Did you get their tune or have driven an hhr with that tune?

I don't know what the spark pack is but my engine has individual coils. One on each plug. I'll try to shoot a video of the exhaust over the long weekend and post a link to it. I don't think having backfire is impossible but the engine has to be tuned that way. Otherwise I agree, it should not backfire if it's not intentional.

 

Note: "nearly impossible"

TSB # 08-06-04-001B is about changing the injectors and programming in 2006-2007 cars. Evidently a upgraded injectors was designed. You can check the part numbers.

 

My SS with the stock muffler had a very audible exhaust "pop" when shifting from 1st to 2nd. Changed to the Flowmaster HP shorty muffler and got the Stage 1 upgrade installed. Still get the pop sometimes. Just not every time like with the stock setup.
Don't think it's anything related to the tune. More likely the straight thru exhaust design.

 

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I did not install their tune yet because I am pondering selling my 2.4 and buying an SS, but I have had a couple good conversations with them and they seem to have their act together. It's definitely worth calling them. Get all your questions lined up first.
Silverfox

 

***** RPM Motor Just put a Black Friday sale on for 10% ...Code AZ18BLF while they last. Limited supply.

Silverfox