I am tuned for a cc305 that ran a 250 shot of nitrous. However, I am currently running a gm847 NA. Also, the compression with the 305 was 10.8. Now it is 11.3. I am getting lean codes on both banks off and on. I assume I have pinpointed the problem. If not, just let me know. I recently ordered a tune from madz28, so everything should be fine after I get it.

 

Yes a tune can cause you to run lean or rich just depends. Get some datalogs and you will have a better idea of where you are at and if the problem is in one area or if it is only at certain loads and RPM conditions

 

Then I guess I shouldn't worry about a tune-up until I install the new pcm tune.

 

I don't think it should run lean if it's working in closed loop. Fuel tunning is mostly done on the PE tables and that only affect AFR at WOT.

 

Thats the weird thing. If I'm cruising, the light will come on. Then, if I slam the gas into WOT, the light turns back off.