OK, humbly asking for some help here with a weird problem, I'm sure I am probably overlooking something but I can't tell what.

To start with, I am not an EFILive newb. Have tuned my LS1 very successfully, running COS, also tuned my Duramax. So this is not my first rodeo.

Now to the problem. My sons Tahoe was getting 7 mpg. Took a look at the fuel trims and o2 sensors - one was a little lazy. Since the truck was stock except for headers I decided to say screw it and just convert to SD and then tune for some lean cruise - mileage problem fixed.

OK, long story short, no matter what I do, the AFR is stuck right around 14.0 as verified by the LM1. LTFT's are +20percent, but still runs 14.0 no matter what?

I have tried multiple successive changes, including:

1. Modified Stoich
2. Modified injector flow rate (did not actually modify injectors)
3. Modified VE tables

Of course, I unplugged the MAF and turned off CAT protection. Also modified PE enrichment based on modified stoich - BTW, also runs about 14.0 in PE mode.

What am I missing? Seems no matter what I do the computer maintains about 14.0?

On a related question, why are the O2 sensors cycling when the truck is running 14.0 - they should be way out of range by that point?

Attached is a recent log file and the most recent (maximum changes) tun that has no effect on the trucks running.

Screenshot of relevant portion of log file below.

Any help would be greatly appreciated.

Thanks

Tim

Click image for larger version.  Name: Tahoe screenshot.jpg  Views: 282  Size: 243.5 KB  ID: 16078Log_0004.efiLog_0004.efiTahoe.tun