Header crack& low o2 #s at idle

[NorCalTurbos]

After checking every vac line I noticed I have a hairline crack at the drv side header could this cause my o2 reading to be low? at idle it bounces around between .50-.75 motor also shakes a lil at idle

 

[salvageV6]

Look at BLM's on the scanmaster they usually go to 160 with a big enough leak.

 

[peterkin]

With a crack in the header it becomes an exercise in futility because of the extra oxygen in the exhaust stream from the crack. The 02 sensor reads that and the ECM uses that information to try and compensate to get to the target A/F ratio. The ECM will keep adding fuel to richen the mixture. That's why your readings are low at idle. Pull it off and get it welded up.

 

[NorCalTurbos]

Thanks bro, this has been a real headache for me it happened at the same time I did a few upgrades I thought the exhaust leak was coming from the cat, finally I found it and everything you said makes sense thanks again