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-   -   Carbed LS swap Backfire (https://67-72chevytrucks.com/vboard/showthread.php?t=720824)

RRC 10-23-2016 11:54 AM

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.

Andy4639 10-23-2016 12:09 PM

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:

RRC 10-23-2016 12:19 PM

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.

davepl 10-23-2016 01:47 PM

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.

RRC 10-23-2016 02:16 PM

Re: Carbed LS swap Backfire
 
Quote:

Originally Posted by davepl (Post 7749948)
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.

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

davepl 10-23-2016 07:29 PM

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.


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