Well, I decided to get my car dynoed today. I took it to Real Performance Motorsports, and they strapped it to a DynoJet. Here's the results of the three runs:

http://openil.sourceforge.net/Dyno1.jpg
http://openil.sourceforge.net/Dyno2.jpg
http://openil.sourceforge.net/Dyno3.jpg

So, as you can see, my car is running wayyyyyyy rich. As soon as the guy got on it, the A:F ratio plummeted below 10:1. I have 30# injectors in my car, though Ion (MadZ28) programmed for them. Hopefully we can get the tune worked out soon. The previous owner said that with the stock injectors and some halfway done programming (not by Ion), the car was running somewhere around an A:F ratio of 10:1 but didn't go below it like that. What kind of things should I be looking for that could be wrong other than the tune?

 

What does the fuel pressure look like? Does it match what you told Ion you were running with the 30# injectors?

Anything that make the PCM "think" the engine is running lean will cause your problem as well. If the MAF calibration is screwed up, and it is under-measuring actual air flow for example, it causes the BLM's to rise above 128, and when the PCM goes into PE mode (WOT) the BLM's from the high load Cells are used to fuel the car. Ditto with exhaust leaks and misfires, although that generally affects only one bank.

You are running at least 30% excess fuel... assuming its not worse than the 10.0:1 that the wide-band is limited to. The PCM is not capable of adding more than 25% excess fuel via the BLM's.

 

The fuel pressure was running around 43 psi today, which is what I told Ion.