ECU Help???

[art leong]

I got to the track Friday night. And devoloped a problem. I'm totally new to the tuneable electronics. So I didn't have a clue about what to do about it.
The car wouldn't make any power in the lower rpm ranges. Similar to a carburated car with out an accelerater pump. Seems to be lean very, very, lean in the lower rpms. Once the rpms get to around 4500 it runs great. But It won't even spin a tire in the water in first gear. It breaks up bad. Seems like a lean condition to me.
This a something that happened overnight, it didn't do this before. My biggest problem then was traction.
The data logger is telling me the air/fuel ratio when its running bad is at 15.94 to 1 or above (this is the highest the sensor reads) Bad when it cleans up goes down to around 13 to 1.
When it cleans up it revs good to 7500 when I shifted it drops down to 5200 and revs fine.
The only changes I made to the car were adding weight to the front end. Bigger battery etc and changing my air intake setup. Neither of which I think could cause the problem.
Tomorrow I'm going to take my data to the guy that setup the ECU in the car. And see if they can figure what happened. But I don't have complete confidence in them.
I'll need a crash course in tuning these ECU's. Maybe someone can help a little at the southern racers race at Silver Dollar Raceway
Any ideas???????