Just got my car back from transmission shop4L80E, now trying to tweak the PCM4Less MAF tune I got. The car runs great, better than ever before. I ran some logs of normal cruising and adjusted the MAF tables, originally blm at idol were 139 and on acceleration pretty much 114. Now the BLM's are 124 most of the time so the changes improved the tune. My question is after accelerating aggresively on deceleration with no throttle the wideband says 12.0-12.5 for a while until I decelerate to about 20-30mph. Will this rich condition on decel give me a problem passing emissions and if so, how do I lean out the mixture.

Also on 80% full throttle, the boost reached about 9psi andthe wideband stayed locked at 11.2. is this too rich for a supercharged engine?

 

My app... 97ss 383 - D1 MM6. I also (once) had an OBD1 PCMforLess tune. It did not work for me (the flash pulled to much timing). I have tuned my OBD2 with success with use of a DynoJet WB. I too have an afr of 12+ when cruz w/ throttle closed. Sometimes 11.5 after an event of heavy throttle & then close. Lack of air will drive the afr rich wnen closed. When the throttle valve is opened, the afr goes lean with air flow. My afr @ full load (~14 to 15 psi) is approx 12:1. I think 11.8:1 is good. I have very good throttle response and heavy wheel spin in 3rd gear with open exhaust. The GM service manual has a very good description of PCM function. It helped me with my flash. Hope this helps. B.

 

Thanks, I'll check out the GM service manual. So far I'm pretty pleased with the tune from pcm4less. I'm gonna have to modify the PE table to lean out the 11.2AFR at WOT to around 12-12.5. When I ordered the tune I told him 12-14 psi, but it looks like with the big FMIC I'm only getting 9-10psi maybe thats why it's a little rich, either way it's close. As far as timing I have no retard happening, and in the log at 5000RPM it has about 29 degrees. Is that conservative for this setup or about normal.

 

Stay 12:1 or richer on the air fuel for safety reasons. Most boosted stuff I have played with worked best in the 11.5-12 range anyway. The extra fuel is there to cool off the pistons at wot in a boosted app or n/a for that matter. The leaner you go the hotter things get, and its easier than you think to find the limit (broken parts).

 

29* time adv is low @ 100+kpa (But, that's just me). I run a large Spearco IC, and, I run 34* @ 100kpa. PCMforLess usually dials in a low advance for safety that I cannot live with. Can't really blame him. On hot days I run a Methanol/ H2O spray. I have converted to Evans NPG cooling and external crank drive vac pump. B.

 

He's running 9 psi of boost, thats around 165kpa (1-bar map sensor)...
You'll probably be down around 20degrees with that much manifold pressure.

 

Thanks everyone for the info I'll bring the WOT AFR up to 12.0 As far as timing I guess I'll leave it where it is unless I get some retard after leaning out the mixture to 12. I can't believe how good the car runs with the new setup 72 pound injectors and LTCC coils and all the info/software that wasn't available when I retired the car years ago. This site made it possible with all the things I've learned from reading.

 

Aim for 11.8 unless you have a dyno to check the output. No reason in running leaner unless you can verify a power increase. I was just saying I would not try to go leaner than 12 not that that was a target.

 

I run no leaner than 11.8 too. For safety sake you should assume there could be a 10% variation on each cylinder's AFR, so if they average out to 12 you could really be seeing over 13 in a cylinder which is very bad. As stated, you wont loose any power dropping under 12 to a safer level.

 

Sounds like you are not entering DFCO on decel, have you checked your datalogs for MAP readings when transitioning to 0% TPS from cruising? Check your injector PW and spark timing when at 0% TPS, PW should go to zero and timing into the single digits when in DFCO. You'll need to compare you MAP readings and adjust the DFCO parameters accordingly it will engage. If it's not entering DFCO, then given your large injectors, even a very short PW would be dumping lots of fuel (compared to stock) which could easily account for very rich readings during decel.

 

I don't think any states measure emissions during decel.

Might hurt your cat in the long run, though.