I put my swap on the road this time last year, it ran fine so I didn't invest much time in tuning. LTFTs were +1.x to 10% both banks. However, a coating of black exhaust residue kept cluttering up my rear bumper cover.

This seemed odd...the PCM was commanding more fuel w/ the positive LTFTs, but it was blacking up my bumper. It did this both with the brand-new AC Delco front O2 sensors (no rears) and with the brand-new Denso fronts I swapped in at the end of the season.

I decided this weekend was the right time to take a pop at LS1 tuning, starting with Speed Density. I disconnected the MAF, shut down P0101-103 SES lights, and copied my Hi-Octane spark table over my Lo-Octane table (PCM sets Adaptive Spark to 0% when the MAF error is set).

My LTFTs immediately went big-time negative everywhere...like -15%. I drove it the mandatory 100mi and they didn't change, still way negative w/o the MAF running. I re-checked fuel pressure and I'm still at 58psi rock steady.

I did the math in Excel, carved up my VE table into cells as indicated in the fuel trim cell KPa/RPM numbers (copied from '02 C5 config, F-body settings are crap), and started revising my VE table accordingly.

After three iterations of run/revise/flash I had the LTFTs in the 0.8-1.6% range everywhere...the car didn't feel any different that I could tell, but the exhaust note changed somewhat. Interestingly, all VE table revisions were *reducing* from the factory VE numbers, even with my TR224 cam...I expected to need to increase these to account for the bigger cam.

I then re-connected the MAF and reset the PCM. LTFTs immediately came back up to 5-8% everywhere. I didn't get more than 30mi, but I had plenty of data in most of cells 1-11 showing a mean of 8.xx% with a fairly small StDev, so I bumped the MAF table by 8%. For the remaining ~20mi ride home, LTFTs were back to -0.8 to +0.8. We'll see if they stay that way.

The throttle felt a bit more crisp after the MAF was back on and that last software tweak. The real test will be if my rear bumper cover stays soot-free.

Conclusions for now:

1.) About all I can figure is that the IROC y-snorkel and cut-up airboxes throw off the MAF calibration relative to the 4th gen airbox.

2.) It's very likely I'm still buying Winter-blended fuel w/ MTBE alcohol in it, I'll need to re-test when the last of the stocks are definitely gone and I'm running straight gasoline again.

 

Interesting is about all I can say. Some day I will start in with some real tuning myself, I still need to study up on it some more, and threads like this are great for just that. I have a couple of exhaust leaks that have been haunting me since day one, so as soon as I can afford some LT's and have a new Y-Pipe made and have gotten rid of the leaks, then hopefully I can start in on some tuning.

Hopefully some more people will reply. Did you put a thread up like this over at LS1Tech.com? I know over there it will get more responses.

 

I used the LS1Tuning.doc from ls1tech and it's great stuff. I posted it more for sharing than for responses, hopefully it will help someone down the road.

 

I like your style.

 

I am inerested in changing my downshift threshold. Any thoughts?

 

I can tell you from experience that the MAF is easily thrown off by any changes in the intake ducting. It must be recalibrated. I used a piece of ABS piping and a K&N filter for my intake duct and the MAF was of by about 10-15% everywhere from the table that I had.

The VE will also be way off whenever you change a cam. If your using a more aggressive cam, then the VEs will likely fall in the lower rpms. As you probably know, the VE is a real pain. Whenever you change something, the VE tables must be changed to closer match the actual VEs.

 

Mine's a manual trans, so that setting is in my brain instead of the PCM...

Not much help, sorry.