[Fredness]

OK folks, I've started tweaking the '05 program from scratch since the 2 hours of street data-logging suggest the K&N AirCharger intake and MBRP Exhaust have MUCH greater flow potential than the factory pieces. I'm thinking it's 75% intake, 25% exhaust since I have the second cat AND resonator. The short and long term fuel trims are showing a lot of fuel being taken out, so I'll have to remap the MAF and do some tweaking.

Bad news: You can't have a generic flash for the intake (may do fine with just the exhaust).
Good news: There is more power to be had!!

 

[whynotthinkwhynot]

I thought that 14.7:1 was a bit much, but that's just for start-up right?

I may have some term confusion you can help me out with Fred. This comes from being an electrician, and not having read an FI manual in a long time. I'll go with what I'm currently thinking and you can correct me:

Closed loop= O2 sensor feeds back info to the ECU to correct F/A changes due to atmospheric changes.
Open loop= O2 sensor not feeding back info to ECU, motor runs on ECU map without correction, like at start-up.

 

[Fredness]

You are practiacally dead on, but here's the detailed look:
14.64:1, (but who's counting []) is used for ALL closed loop functions unless there is an event (cat overtemp, etc). This is because all emissions are lowest at stoich. If you go lean (to improve mileage), your CO and HC's are absolute lowest, but NOx (Oxides of Nitrogen - a key SMOG element) go through the freakin' roof. I'm sure, that if our cats could remove it, we would already be running much leaner. Since we are running at stoich, I have to assume that we are incapable of running in a "lean-burn" mode. More research is needed.

Closed Loop: Engine temps at "operating" levels, cats warm and ECU uses the first o2 sensor in the stream to compare to the command table (1.0 lambda is stoich). The O2 reading is constantly fedback to the ECU and fuel trims are adjusted to keep the engine at stoich. There is CONSTANT fluctuation, so the readings will swap from .995-1.005 (ish), so the reading has some "hysteresis" (roughly speaking, a feedback lag). This lean/rich/lean helps keep the errors down.

Open Loop: Regardless of temp/cats, the engine is kept at a specific fuel ratio from the command table (.860 lambda or about 12.44:1) that is read by the O2's (they just don't have a say in the output). The A/F ratio is determined by the MAF voltage, IAT readings (to determine the MASS of air moving) and fuel lookup tables that decide what pulse width to use on your injectors. This mode is used for warm up and max power. Now, the O2 sensor readings do go BACK to the tables for correction. So, if you change your MAF and the O2's sense a change in open loop, your long term fuel trims will actually make changes, just much later in the process, and they are AVERAGED corrections.

 

[whynotthinkwhynot]

Thanks Fred, I was right about some things, but wrong about others. I thought that HC emissions came from lean conditions- not the other way around. I never really read anything about emissions.

Thanks

 

[Fredness]

HC and CO are formed from unburned fuel, so they're from a rich condition. Found out that the NOx cats are some crazy salt that absorbs NOx during lean burn and swaps it during a rich burn cycle. Nutty and expensive.