I have an 03 with intake, spacer, headers, and catback. After the install of the headers and exhaust I felt like the car was a little sluggish so I reset the ecu by unplugging the battery for several hours. After I reset the ecu, I started the car up and it wouldn't idle. The engine would just start up and die. I drove for a couple of days hoping that the ecu just needed to relearn for the mods, but I had no luck. 70% of the time I started the car it would die on me.

So, I thought that the car was probably running leaning and decided to take it to GT Motorsports to have them install a UTEC, wideband, and perform a tune. Sam at GTM noticed that the car was running really rich at idle(11.3-13.5), which he thought was really odd. But, he said that the AFR's looked fine otherwise. He tuned the UTEC to lean out idle and leaned out the fuel a little up top. I put down 145whp and 148wtq. Sam wants me to come back to help diagnosis what is going wrong with my car, and he mentioned that the car is throwing a code saying that bank 1 is running rich.

So, I'm driving home and I notice that my AFR's are reading as high as 9.7 at full throttle above 4k rpm. I have no clue what's going on with my Z. Does anybody have a clue as to why my car is running so rich?

 

faulty O2 sensor??? did you change the cats? did you remove the O2 sensors at any point in time?

I *think* you can use a tool like CIPHER to tell the stock ECU to use one bank or the other for making adjustments - you could try that...

I know you can use CIPHER to read the AFR (but not sure if that will work with the narrow band sensors for your 03; they are wideband in 04.5 and up only). In any case, you'd be able to tell if the driver's side or passenger side is way off (then you know which O2 sensor to replace).

 

Stock cats, but I'm sure they pulled out the 02 sensors when installing the headers and when they put the additional bung for the wideband. Sam at GTM thought it may be an 02 sensor as well, but he said that it seems to be responsive.

Wouldn't a bad 02 sensor mess up my AFR's across the board instead of in certain parts of my rpm range?

 

No way to know - I don't know anything about how the O2 sensor works or why they are sensitive to an impact or what goes wrong when that happens. I do know the service manual states that if you drop one to the ground from over 24 inches or something like that, don't even bother trying to re-use it. Ask Sam if someone dropped it.

I'm pretty sure (well not really sure) that the stock ECU only uses one of the sensors to make adjustments to the AFR. I would try to swap them and see if the situation improves. if it does, then you found the problem and didn't spend a dime diagnosing it. If you decide to do this yourself, you should use anti-seize on the threads and get a special O2 sensor socket (standard piece at Advance auto parts or Autozone) that allows you to remove and reinstall it without the wire getting in the way.