What AFR?

[torq455]

Help! 04 GA SE 3400 with a couple of external mods only. reprogramming the pcm and need to know what AFR to command. Supposedly, say during the 1/4 mile it starts at 12.9 and drops to 12.0. From what I hear, the command vs. the actual AFR is different. What should I program this at?

[sharkey]

generaly you want 12.5-13.2 under WOT on an n/a engine for best power. without a wideband o2 sensor, how does the pcm know what the air/fuel ratio is and how can it compensate for it??? a narrow band o2 sensor just shows anything under 14.7 to be rich, but cant indicate how rich.

[torq455]

yes, but there's what is commanded by the pcm, and what the engine is actually getting, right? i'm trying to find out what i should tell the guy programming my pcm. stock has to be on the rich side. yet i find that 12.9-12.0 is good at WOT. but if that's really 1 point high compared to what the engine is really seeing, then it's really getting 11.9-11.0 afr. so should i tell this guy to go 13.9-13.0?

[SappySE107]

You can't do it like you want as it doesn'twork that way. Don't guess. If you don't know, set it conservative until you get it on a wideband setup.

[MMGT1]

Could tell him you want a comanded of 12.9 @ WOT. As Ben has stated you can only do this properly with the aid of a WB. I was commanding 12.8 on the narrow band and with my new wide band found I was only getting down to 13.4-13.6!! So the NB's are completely useless. And no two cars will read their NB's the same!! For example: your car may read, let's say, 910mv @ WOT and mine may read EXACTLY THE SAME, and with a WB yours may be 13.0 and mine would be 13.4......making them, as said, COMPLETELY USELESS!!

[torq455]

so ya'll are saying that i should just leave the stock afr alone to be safe....

[gectek]

but if you were looking to be safe, you wouldnt be modding really, i mean that is what it is all about, pushing the limits and asking questions. safe is a realtive term. as long as you have a reliable starting point, you can tune as much as you want, and some engines will take to tuning mods more than others, some come from the factory with KR, mine will pull up to 6300 RPM from the 1-2 shift and never see any KR, and thats with the 1.5 pcm from DHP which is supposed to have more aggressive tables and has to use premium fuel, well i dont run premium and i still dont have problems.

[SappySE107]

Elevation, quality of local gas, how close GM was to spec (tolerances), etc. Tons of variables. The deal with the commanded AF is that it uses calculations based on the tables, the +- fuel trims for long and short term, and your spark timing which is only variable upon knock. Its open loop. So while its not accurate to read the narrowband O2, its also being ignored by the ECM as well.

This is why you don't tune WOT first.

[sprucegagt]

/\ Finally one of them is seeing the light! lol

Help! 04 GA SE 3400 with a couple of external mods only. reprogramming the pcm and need to know what AFR to command. Supposedly, say during the 1/4 mile it starts at 12.9 and drops to 12.0. From what I hear, the command vs. the actual AFR is different. What should I program this at?

As others have said you will need a wideband to get an accurate AFR. The reason why the commanded AFR is different from the actual is the MAF table being off while your in PE. If you had a wideband you can correct this so the commanded AFR does match the actual AFR.

FYI, the stock PE commanded AFR's are to aggressive in the 04 GA. You don't need to drop a full AFR point while at WOT unless you plan to be on it for more than a minute.

[torq455]

so if the AFR were to stay at 12.9, for a once in a while 20 second WOT burst. that would be better than a decending AFR? like i said, i don't get much of a chance to even run a full 1/4 mile.

[SappySE107]

You would have to run it on the dyno and see what the engine wants for your 20 second burst (which better be more than 1/4 mile!). I found on the 3.1 (obd1) that it liked to be richer down low and lean out at higher RPM. That could be because of the stock tune being richer in the MAP tables too:P

[MMGT1]

"Lean is mean" the saying goes. The sweet spot for torque on gas burners is 13.2:1. I run 12.9 @ WOT to keep it safe. This is from 7000hz to 11500hz. The most I see is 9000hz but you want to smooth the table the rest of the way up.

This is how you tune a V6:

There seems to be allot of methods to tune the AFR on the V6 cars. Since these cars don't yet have an open loop table like the V8's and the V6 (4.3) trucks, the commanded AFR while in open loop is all over the place when not in PE. In PE the commanded AFR will be were you set it.

This is what I found is the best way to tune these cars. First leave the VE table stock. Then zero out the Power Enrichment PE Enable > Delay vs. TPS table (some models will already have this table zeroed out). Set the PE Enable TPS > Hot to 0% (at all rpms). Set the Base AFR vs. ECT to 14.7 at all temps. Zero the Add vs. Tps (note the values in this table add to the Base AFR vs. ECT and leans the AFR). Then zero out the Add vs. Rpm table.

Now install the wideband in place of the stock front 02 sensor, or the right front if a rear drive car (this will put the car in open loop). Flash this new file, then warm the engine to operating temp. Start scanning and reset the fuel trims. Now the commanded AFR will be steady at 14.7. With the Maf AFR histogram open, drive the car at part throttle to fill the histogram up to ~7500 hz. Try to accel & decel smoothly. Then copy & paste the Maf error % histogram to the Maf table using paste special multiply by %. Once you get the AFR close to 14.7, then use paste special multiply by % - half. For the low end of the Maf table that you didn't enter, just enter the error % from the lowest airflow hz cell that you did enter. So by now the part throttle AFR will be ~ 14.7.

Now change the PE Enable TPS back to stock (or were you what it as some models have the low rpm enable at 100%). Change the Base AFR vs. ECT to 13.0 at all temps for NA, or 11.5-11.75 for a boosted engine. Flash this new file, connect the scanner and check & reset the fuel trims. Bring the car to a dead stop, use the VCM controls to put the trans in 2nd gear. Now go wot till your max rpm desired. Then copy & paste the Maf AFR error % to the 7625 hz & higher part of the Maf table. For the freq. hz cells that the scanner skipped over, just average these cells. For the higher freq hz cells of the table that you didn't enter, just enter the error % from the highest airflow hz cell that you did enter. Once you get the AFR close, use paste special multiply by % - half.

Unlike the V8's and V6 trucks, if the part throttle fuel trims are negative by even a small %, you could have negative LTFT at wot. This is why you need to get the open loop part throttle AFR close to 14.7 BEFORE wot tuning the AFR.

When going to wot from a dead stop there will be a lean spike at first (under 7500 hz) that is normal if you first got you part throttle AFR right, this is caused by the split sec. delay for the richer exhaust to reach the wide band.

Now install the stock O2 sensor. If you did everything right, your LTFT's should be close and will lock at 0% @ wot.

[SappySE107]

Interesting method. I haven't heard of that one but I don't tune OBD2 so I am not sure how the computer reacts to what you are doing by removing the O2 signal to the ECM. I know the OBD1 would take your - LTFT and add it all back to 0 (128 in obd1). This way it would only add fuel. If your LTFT is adding, it would keep all of that. Sounds like its less safe for 60V6 OBD2 if you can actually lean it out more using your LTFT from cruising around.

[MMGT1]

It works!! Getting that 14.7 is key with our cars. Unpluging the "factory 02" puts the car in open loop without having to go SD. (very hard on trans!!) Once the 02 is back in the trims will be very cose and WOT will be "PERFECT".
This dissables all trims in the OBD2 as well. No need for trims when you tune with a wideband...

[torq455]

ohhhh well DUH!!! why didn't i think of that!!