while this is not a W-body but it is an interesting observation... this is a before video of a basically stock tune nothing but getting the trims away from +11 and closer to 0 but still fought 4* of KR on that tune till I found the issue.


then 3 weeks and dozens of tunes later at the same on ramp this is the same truck and similiar weather.


The only mods on the truck is headers bigger dual dumped exhaust and TB spacer and smoothed and blended TB removed restrictor and 4 in tubing and cone filter and egr and evap and bed cover.

The tune in it currently has changed the shift points from 25 mph to 40 mph in first and 65 to 80 in 2nd which the built trans seems much happier with. TQ management has been all but removed and ironically that is how the KR # have steadily came down and held down. I have added up to 10+ degrees of timing to the base map and see 40+ at cruise. The fueling is finally close and is usually +-2 or 3. figured even though it is not a regal it is a good case for indiviual tuning and what can be accomplished when enough time and energy can be put into a vehicle and its tune. if you have any questions i will admit I am no expert but slowly picking it up as I go and this is the only before and after I have that is really noticeable. mid range and part throttle are still not quite dialed in but they are getting closer and the seat of the pants dyno likes the improvement.

Can you post up a screen capture of your scan showing the problem area. Any time you make a change to the flow you can effect the AFR. Opening up the exhaust allows more air in and out. If you have a wideband O2, what is your AFR at cruise and WOT? If the KR showed up after the trans tune, it may be the trans that is causing it. False KR. I'm assuming you do not have a boosted engine. So KR should not be a huge issue. What transmission you have? A shift kit may clean up the KR by shifting faster.

After doing some more tweaking I hit the ceiling on the tune it started spitting and coughing on the last tune I put in so I back stepped it and it is about as good as it will get I will post more videos later but it is getting better mpg and is running 40* of timing at cruise which seems to be the most it will tolerate