pcmhacking.net

I've been reading up on a ton of different guides and approaches to tuning the LS1 GenIII PCMs depending on tools, software, and hardware available. I've settled on using LTFT/STFT and driving a ton.

PCM is running OS 12212156, started with a stock file from a 2002 M6 LS1 car. The only fueling modifications are to the VE table, MAF Calibration, and Cylinder volume. The rest are tach, speedo, and DTC changes. I've got my VE tables with +/- 3, and my MAF calibration ended up being about 5% away from the stock calibration. I did end up changing cylinder volume since I have a 5.3 Block, but did all my VE and MAF Tuning after that.

My issue is whenever I try to switch back to a blended mode (Dynamic Airflow RPM @ 4000), the engine just will not idle like it did in MAF only (Dynamic Airflow @ 100 RPM) or SD (MAF Fail Frequency @ 0). It also won't come off idle without spitting and sputtering and hesitating at random RPMs.

What I don't understand is how smooth it can behave in SD or MAF Only, but blended is awful.

Hoping someone has an idea on something I'm overlooking with what I'm trying to do here.

LTFT/STFT is probably the least accurate way to do it. Do you have a wideband? You really need instantaneous data. That its running like crap after changing things is telling me your changes are taking it further away rather than closer to accurate. But thats an over simplification and a few assumptions on my part about exactly what you've got and what your doing. But it does sound like your tune is a fair way out with the spluttering.

Yeah, no wideband unfortunately.

What boggles my mind is it's only spitting and sputtering in blended mode. SD only no issues, MAF only no issues.

It's really running phenomenally in SD or MAF only modes.

Well, not sure how it happened, but I was comparing the stock bin to my tuned bin by hand, and came across some dynamic airflow parameters that were mysteriously changed. EFI Live and TunerPro comparisons returned no differences with their automated 'Show Difference' tools in these portions, so I went back to the stock file, and copied only the changes I expected to be making one by one.

Changing DTCs, Tach, Speedo Calibration, VE Table, MAF Calibration, CAGs, VATs, Cylinder Volume, and Fan type from the stock file, and the car started performing like I had expected. I definitely need to Wideband tune this, but wanted to get it at least close until I can get it somewhere or buy the equipment myself.

Hopefully this helps someone else who sees weird behavior out of the blue to verify your file didn't get tweaked in a way you don't expect. The two parameters I ended up seeing different that I didn't change that made me question things was the Dynamic Airflow Steady State High/Low RPM and MAP values. I don't recall changing them, but