History: 1994 blazer 4x4 5.7 ltr. I passed smog in 2013 with flying colors. New catalytic converter has to be replaced. Prior to that ..I replaced the EGR valve, 02 sensor, cap rotor, plugs wires, rebuilt the TBI unit...it would not pass. Once the CC was put in...tech said it was running really clean... I dont drive the truck too often and I just replaced the battery 1 month ago...I drove it for about 25 minutes and took it in for a smog check....and did not pass...the tech said it was running really rich.....I am pissed!! Could replacing the battery take the computer out of code it is making it run really rich..? This sucks ...I just want it to pass so I can sell it....I live in CALIFORNIA..
Please advise.....This blows!!!
other replacement parts: New fuel pump,

 

If you could get it hooked up to a scanner and pull some data that would help. It could be from a bunch of things but I would start with getting data. You could also check the plugs to see if any of them are discolored dark. Anything darker than a light brown indicates it is running rich. In a TBI engine that could be caused by very dirty injectors dumping fuel rather than spraying it in a cone like spray, bad pressure regulator, and/or bad O2 sensor. It may be worth just running some good fuel system cleaner (I prefer sea foam) through it to see how it acts after that is done.

 

I would say that it is a temp problem. Sensor thermostat or you didnt run it hard enough to rebuild the fuel map.

 

You're absolutely right that it could be a temp issue as well. Normally in TBI engines if the coolant temp sensor is bad or reading cool enough to run rich like that the gauge will have problems with reading correctly as well.