AFR Jumps way high in boost
 

Hi I own a 2008 Cobalt SS/TC on E85. I bought the car on Craigslist and supposedly it is tuned for 25psi and E85 and has the upgraded fuel pump and injectors and all of that.

When I go into boost suddenly or aggressively the afr jumps really high (~29) im not sure if it’s a sensor problem or if I’m maxing anything out while doing so? If I ease into boost the afrs seem to be fine but again I’m not sure. (I’ve had the car for months and have driven it at WOT multiple times but I just programmed the gauge for AFR and I’m surprised it hasn’t blown up yet? Thanks for any info

Yeah that's pretty scary. You need to check that out. 29 is what it should read when the fuel shuts off after you let off the throttle and the injectors shut off.

are you sure its not between shifts or when u take ur foot off the gas suddenly? cause that would be normal. if its doing it when ur on the gas, ur going super lean and u need to stop it now and get someone to check ur tune

With a 29:1 AFR under throttle, the fuel mixture is too lean to support combustion. That will result in misfire on all 4 cylinders and a loss of all power and boost. If the engine is running normally and it's still showing 29:1, you have something else going on.