What changes in computers/ecm?

[klrv6]

OK, I've just picked up a Jet DST programmer for my '99 suburban 2wd and 03 regal. What are the best know parameters to modify or change in order to see mileage improvements? I have already done some work on the suburban, dropped idle rpm by for most temps and bumped up timing four degrees from 2000rpm and 20kpa down. I plan on running some logs via auto-tap and see where the engine load and timing are during 70-75mph cruise settings. The software can touch pretty much every table within the ECM.

I have removed the roof rack and installed an efan with positive results. Just the roof rack and and new michellin tires yield 21-22 mpg (scangauge) on the highway.

Where should I start tuning for max mpg on this thing?

[MetroMPG]

Hi klrv6 -welcome to the forum.

I can't answer the question (not a PCM expert), but there are a couple of members on the board who are. Hopefully they'll see the thread and pipe up.

[SVOboy]

Welcome to ecomodder! I played with tuning a while back but didn't really get anything, think you need a dyno, some money, and some time to really get anywhere with timing and afr tweaks.

[JohnnyGrey]

The stock program is unable to run anything in closed loop but 14:7:1. GM has a lean cruise mode on ROW ECUs. If you can reflash your ECU or get a ROW unit (if they exist), you will pick up a few MPG highway. I can guarantee that you'll see substantial savings by dropping from 75 to 55mph.