I scanned my basically stock camaro (shorty headers, 160 thermo, and tb bypass) and I noticed that some of my blms are split.. At idle they are like 128 130, which I think is ok. But it looks like as i accelerate they seem to split a little more and go up in the 140's..
I also noticed that after I shifted into third and had my foot on the floor the blms were down to 128, 130 . Why would they be here instead of being up higher like when i initially hit it?
Also what should the blm's be at cruising for best gasmilage?

Sorry if this is basic, just trying to get more of an understanding of the computer b4 I try and tune her. Also getting up to 9* of KR that needs to go away too at high rpms.

 

No one knows? or is my question confusing?

 

When you mash the throttle to the floor the PCM goes into what is known as PE mode, PE = Power Enrichment.

When the PCM does this it locks the fuel trims a 128. That is because it is no longer looking at O2 feedback for trim but is relying on what is in the PE tables for its fuel curves.

There are two fuel trim tables. One is Long term and the other is Short term fuel trim. These trims are calculated by the PCM using O2 feed back. Based on how long the O2 voltage goes above and below "stoich" which is 450mV.

For instance if the O2s stay above 450 meaning a rich condition the fuel trims will go low to take out fuel, if the voltage stay below 450 the trims will go high to add fuel.

It is normal for the short term trims to be updated contiuously as the short term trims contiuous trim to maintain ideal stoich in closed loop. Hence the term short term. The long term trims are not updated as fast and is calculated trim over time based on the feedback from the O2s.


Thats basically it in a nutshell.

 

Well I try, 128 is the magic Number, it's what you start out at in open loop, when it doesn't look at the O2's, in closed loop it is looking at your O2 #, if you are looking see if your O2 # are close for both sides then you tune (spark changes, other changes) till you are running close to 128 or so, during normal driveing. then you go to playing with the WOT and PE tables.

Check these out to read a little more.



http://www3.baylor.edu/~Christopher_...ht/LT1Edit.htm

http://w3.one.net/~roz/cars/z28/tuning.html

 

Thanks guys, I'll have to boot up the laptop in a little while to see more of whats going on.. I dunno really what to look at but TPS and KR which I'm getting up to 9*.
Main reason I asked is that it seems my gas milage kind of sucks and was wondering if maybe i was running rich or not.

 

The larger the BLM value is over a 128, the leaner AFR is, thus if your scanner is reporting 140 plus means your 10 plus % too lean and one reason you have 9 degree timing being yanked out.

Values lower then 128 would mean rich.

You need to find out if a tune E/PCM tune would correct the problem alone or you also need to better the fuel issues and/or find out if all the knock is real or some is false and tune that out.