When I was driving my 3.8L Project Car Mustang I noticed that it was running in a closed loop but Short and Long fuel trim for my Bank 1 O2 sensor was reading -20.31%for STFT and -14.84% for LTFT. Of course, my Bank 2 O2 sensors were in good percentages (both under -5%) I noticed this when I either came to a stop or when I was at idle. When I increased the speed to around 1500 RPMs the Bank 1 Fuel Trims corrected themselves. I just replaced both upstream o2 sensors and I don't have a catty converter. I am wondering if this is normal or if this is caused by a vacuum leak?
