PL/TurboTweak BLM cells question

John Larkin

Sublime Master of Turbology
May 25, 2001
When I was on the data page, I had the car idling. Most of the 16 cells were 128 except for a few on the 3rd row. The top left cell (Cell 0) was highlighted yellow and it was locked on 137. My WB was showing idle AFR around 13.5. I got my instructions out and went into programming mode and changed that cell to 128. It stayed yellow. But the idle AFR came down to 14.7, perfect. It has been a LONG time since I dug into the whys but @ 137 BLM, the computer is adding fuel even though the wideband was showing slightly rich. Once I changed it to 128 manually, the AFR became what I would say is correct for idle. Cell 0 is low MAF and 0-800 rpm; my car idles @ 950 but whatever.

So the question is, why would the car want a rich idle? It idles in open loop like Eric designed it but I see no reason for it to be so rich, not like there is going to be knock retard at idle.

Any thoughts or opinions appreciated.
To my knowledge of 6.1 the NB handles everything up to 70 percent throttle. My guess would be the NB MIGHT be going south. Eric checks in once a day here...shoot him a PM. I have a basic understanding of 6.1 but didn't use it cuz I ran race gas and it eats sensors alive.
Going a little rich on idle can help stabilize it and cover over small problems like small vacuum leaks, tip in issues, other stuff I can't think of. But if your car is in good working order, no reason to not target 14.7:1.
After I made the AF stoich, it was really snappy to rev, no stumble. I thought about it and it must turn yellow when it exceeds some programmed deviation from 128. Who knows, I will take a look next time I hook it up. Thanks for the replies!