general question '97 5.7 fuel trims / timing / etc...

[Boost]

Very seldom do I get to work on much less tune these "old" trucks. My friend removed the Hypertech hand held from his '97 5.7 truck and he says it uses more fuel now. My first though is perhaps the handheld was leaning out the mixture for a bit of power thereby improving the economy OR his truck needs to reset and adjust to the new (stock) program. That being said, is there a way to reset fuel trims (we will check with a Tech2 as well as FS later) and does it matter? Also, if he runs 87 octane will the timing eventually adjust to where he can floor it without pinging? I think under ideal circumstances the GM tune should run more than happy on crap octane. Other things, is my fantasy that higher octane advances timing and nets better effiency based on anything realistic and true? I will look to see how timimg and fueling is controlled on these "dinosaurs" to get a better idea, just wondering. Thanks!

[Boost]

some other ideas, I told him that he may be stepping on the throttle more due to slightly less torque, also I read up on "description and operation" and these have full knock and O2 sensor function (timing and fueling). so in a way a dumb question I guess.

[hog]

Its common to pull a bit of fuel out of the PE fuel multiplier in order to make a bit more power, but that has nothing to do with non PE mode closed loop(reading O2 sensor) operation.

Closed loop operation will trim itself. I'm pretty sure that whenever the PCM is flashed, the trimming starts out at zero.
These PCM's do have Octane Adapt in the code.

the Hypertechs do add a bit of timing, but they pale in comparison to a good PCM tune by a knowledgeable tuner.

there could be many causes of a WOT knock.

peace
Hog

[Boost]

Thank you