Originally Posted by BlueShadow

I had a similar problem with CromePRO and my turbo B18C w/ P28 ECU. While I was tuning my AFR's from 26 in/hg to say 15in/hg would be 15:1. But when I was cruising around in really high vacuum it would read 11:1 or 12:1. But at that point my vacuum was higher then 26 in/hg. 26 in/hg was the highest vacuum column on my Crome fuel map. So I thought it had to do with my actual vacuum being out of the range of my Crome fuel maps highest vacuum column.

Maybe if you rescale the vacuum columns so that the first vacuum column is 28 in/hg or 30 in/hg you can actually log and adjust the AFRs for the really high vacuum columns? I haven't gotten a chance to experiment with scaling vacuum columns in CromePRO yet to see if it will work. But maybe you should give it a try.

Look at your vacuum gauge and when it starts reading rich when you are in high vacuum make a note of what your vacuum gauge reads. Now look at your fuel map and compare that with your highest vacuum column. Post up what your vacuum & AFR numbers while actually driving and your highest in UD.