Lol... Damn... I wish I put the ECM back up weeks ago when I said I was done!

I keep finding cool stuff in the S_AUJP code that ends up going back and forcing me to re-tune other stuff (don't know whether it's a or a )

I've been playing around with the MAT tables lately and during some datalogs noticed the other day that during PE, the BLM would lock to 134, which I thought was curious.

Turns out that MAT table adjustments were getting the BLMs to 134 at high map just before entering PE. I didn't know if it was impacting anything...

So did some searching and came across an old thread of mine regarding PE AFR's...

https://www.thirdgen.org/forums/diy-...drives-pe.html

Which had this little nugget...

I didn't have a WB at that time, so I had no way to really know what was actually occurring with actual AFR.

But digging through the S_AUJP code, I found the option bit to lock BLMs to 128 during PE. Works like a charm.

It makes sense that GM would put that kind of protection mechanism in there, since whatever would be causing the car to run lean in normal driving could be expected to do the same to PE (i.e., clogged fuel filter, bad injector(s), fuel pump on the way out, etc)... But since I'm tuning PE and VE independently and with visibility, it just gets in the way for me.

PE's actually leaned out a little after setting that flag since, with the lock occurring at 134, I guess the ECM was modifying my PE settings a little richer.

Looking at the data, it almost looks like its a proportional modification depending on how far off of 128 the BLM gets locked at.

134/128 = 1.04

Before setting the flag, actual AFR's were around ~12.5-12.7:1. After setting the flag, AFR's jumped up to around ~13.0-13.2...

And 12.7 x 1.04 = 13.2

 

Its why part throttle tune is so important and why it diesn’t hurt to have ur tune slightly on the rich side. If I’m going to the strip or some racing, I typically re-create my calibration but w BLMs locked at 128 for the purpose of consistent fueling.

 

Pretty sure not all $8D need this, but I could be wrong.

I didn't find it in AXXD/C/ANHT when looking to lock BLMs.

This is common practice in the LT1 years.

 

You need SAUJP. And i believe minimum V4 at that.

Yeah the factory 8D masks don't have it AFIK.

I abandoned ANHT a while ago and redid my calibration based on the SAUJP.

 

No, I'm saying I don't think it's necessary in those as it already locks at 128 from OEM. But again, I may have missed it. I only looked briefly.

 

it'll only lock to 128 if your BLM is less than 128 before entering PE. If your BLM is higher than 128, it'll lock to that number. In my case 134. It'll then add fuel (apparently proportionally) to your PE AFR over and above what the PE commanded AFR is.

 

That may be true in SAUJP, but some other $8d I believe it's not. Only mention this in case others read the thread and look to fix theirs but aren't running aujp.

Again, I haven't looked for other references, but that'd be strange if they do this then adjust it later too.

 

Need to look at more of the code, it is as ULTM8Z posted (from AXCN):

RBob.

 

Ha! Told ya I could be wrong. That's so painful to know I missed that. Well, I better fix that whenever I get back into it.