Carbed LS swap Backfire
 

I have a stock 5.3 with a Holley carb. I have tested and researched about all I can find. I have talked to MSD and have also tried a Dayton Sensors smart spark with no luck. Everything I have done to this point has made a difference. But i still have a backfire through the exhaust at start up. Good grounds and 12v, new sensors... i have got rid of the misfire and have a good idle. I have tried different timing curves with the laptop. Im finally out of ideas so here i am looking for any help... I'm sure it's something simple..... also have good vacuum.

Re: Carbed LS swap Backfire
 

Does it only happen when cold? If so check the bolts for the exhuast manifolds are headers which ever you are running. They may have a slight gap in them at startup but once warmed up they close up.
Just a thought.:chevy:

Carbed LS swap Backfire
 

I have a stock 5.3 with a Holley carb. I have tested and researched about all I can find. I have talked to MSD and have also tried a Dayton Sensors smart spark with no luck. Everything I have done to this point has made a difference. But i still have a backfire through the exhaust at start up. Good grounds and 12v, new sensors... i have got rid of the misfire and have a good idle. I have tried different timing curves with the laptop. Im finally out of ideas so here i am looking for any help... I'm sure it's something simple..... also have good vacuum.

Re: Carbed LS swap Backfire
 

Check your cam sensor connector to make sure it's solid, though I doubt it would actually run otherwise.

Have you changed anything about the ignition tables? If your cranking spark were way off, it'd do that.

Re: Carbed LS swap Backfire
 

I'm going to try a different Cam sensor today.... I have tried different degrees of timing at 0 rpm

Re: Carbed LS swap Backfire
 

I don't know that ECM very well but there might well be cranking spark tables separate from the RPM based table.