so after reading all the sticky posts and doing some searching, I am still not sure what is going on in PE. can PE be tuned similar to VE? the reason I ask is once I get my VE and spark running together to get 128/128 across the board, how does PE relate? my understanding of what happens in PE is the following:

1. the O2 sensor is no longer being used and BLM is disabled.

2. the knock sensor is still active and will back out timing if knock is detected.

3. if there has been some correction by the ECM to add fuel in the VE table via BLM, it will also add fuel to the PE to correct and keep from going lean.

now I know that is just part of what is happening here and is probably only 50% right (maybe less) so please help me understand this better.

the reason I state all this is because I wanted to apply similar techniques to tuning PE that I did in VE.

once all VE and spark is good to go, allow PE to come on and look for knock. any place where it is obvious back out timing. also check the plugs and see what color they are. I assume that if starting with the stock PE table that at least backing out timing where knock is seen and checking plug color will keep my engine in a "safe" place until I can get it on a dyno to run with a wide band to get a better handle on what is happening. does that make sense?

 

Correct, the value added at the point of PE entry will remain additive.
From that point on, PE fuel and spark are added per the PE tables as a % of change. It is important that the VE tables be correct to keep the % relationship correct to obtain the "commanded" AFR during PE.
It is possible to get the actual AFR correct by tweaking the tables but it will not match the commanded unless the VE is correct.

Using a WB is the only way to measure correctly. By doing pulls or runs and examining whaere you are and then making changes to the PE tables to get where you want to be.
There is no corrections applied to fuel in PE except as mentioned above. It just goes by the numbers once in PE. So if you are lean it will stay lean.
Not using a WB can be risky or keep you on the very rich side to stay safe but you won't be optimizing your output.

 

As JP said, the ecm uses the VE table as its starting point for PE fueling. While not completely necessary, I like to get the WOT areas of the VE table perfect so that the AFR I've commanded in the bin is actually what I'm getting. This is quite easy with a wideband. (There are two PE tables that are used to command the PE AFR).

First, I make sure that the part-throttle areas of the VE are accurate. Then, I command a flat-line PE AFR for WOT (something RICH to be on the safe side), hook up the wideband and datalog the results. Then tweak the 90-100 kpa regions of the VE table, and repeat until it's perfect.

HTH