5.7 Vortec backfire/shudder

[east302]

You can get an obdii reader and download an app to read codes and look at the specifics.

I use a BFX Bluetooth adapter ($30?) and CarGauge Pro ($10) for android. DashCommand is another one, but on either one you need to download/purchase the extended GM parameters for more detailed data. That's another $10 or so. Both will read the CMP retard offset (many don't).

Either will pull the history codes which would be a good starting point for narrowing down your issue.

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[YukonandtheHOE]

Pull the throttle body off, if you smell raw gas in the upper intake you have a spider issue, the blinking CEL is indicator from the down stream o2's picking up a rich condition usually un wanted gas getting in potentially dammaging the Converter (that you dont have)? So is your rear o2 in a cheater plug? Your engine will ultimately be trying to lean its self out and retard timing to correct the down stream rich condition. Making driveability bad..

 

[bartonz]

Last update. Changed the cap, rotor, and coil. The shudder is gone. No idle fluctuations to speak of. The backfiring persists still. I got a code finally and it's the o2 sensors. That should have been accounted for with my PCM tune since I went with no cats. I also have spark plug non foulers in place. So to have an o2 sensor issue is very surprising. Right now I just deal with the overly lean conditions on cold start, for I am done throwing time and money to a lost cause. If anyone has similar issues reading this you are best off to keep all factory aspects in working order. No stupid cat deletes nor egr. Nothing at all if you want a diagnosable vehicle.

 

[TigerEyz3]

Assuming your backfire is through the exhaust, it sounds like you're running rich (fuel igniting in the exhaust pipe). Given the "lean start condition" I'd seriously consider having your programmer hook your vehicle up and adjust the fueling across the board (start, idle, open/closed circuit). May or may not be related to your cat/egr delete....just a thought.