Originally Posted by WS6FirebirdTA00

silverhawk, thanks for the info i wasnt sure on the calculations. i knew it was based on cooling of the resistors in there i jsut wasnt thinking about that at the time of the post. thanks for correcting me though. yes the pressure play a fairly large role you are right, but in the last calculations i used for airflow=density*area*velocity and the density calculation was done at density=pressure/gas constant* temp in degrees R the changes i put in for pressure didnt effect it a whole lot, although i coudl have done it wrong i didnt have a calculator i did it in my head.

i talked iwth my thermo professor and he said it would be ok to disreguard the humidity levels becuase that only makes up a very small % of the airflow. i agree it does throw it off and i feel like it should be accounted for but he said for these calculations it could be considered negligable without issue.


mr dude, if im wrong thats great, and i hope that i am. just as far as i knew the car didnt make changes in temp based on the IAT sensor. i havent logged in large temp changes but i have gone 40* changes and everything seems to be right in line still. i just assumed that the car didnt compensate. my friends s10 doesnt have a maf and in hot temps his fuel trims go up, but that coudl be how the s10 is. yeah i know lots and lots of car, prob 75% of the cars on the road, dont have maf sensors, i just assumed that the temp change was in the error resulting in them to change to maf sensors to take this error down. i know the IAT keeps on changing but i was saying for a majority of the tune at xx deg.

i dont have my license so i cant just go out and log in temp changes. although from what i have seen its been ok. from what i have read, i didnt think the computer could do anyhitng to the airflow on temp, i actually posted and asked if the IAT sensor was used to calculate the airflow. the temp is the biggest error so if thats emiminated then great. im just going on what i was told, but my first thought was SD would be fine becuase so many cars ran on it anyway.

i dont want you guys to get all jumpy at what i say, this is just what i have been told by a lot of people and i just got into this tuning stuff so i dont really know all the details or computers calculations. what i was saying about without a maf the car cant account for atm condition changes i was thinking about temps. like i said this is just how i saw it on my friends s10. 30* out trims were at 0 -1 and at 75* they were at -4 -5 consistnetly. in a 70* swing of temps the fuel only changes by 8.5% so its not so much taht a car wont beable to run, just run richer, so i thought cars were tuned to be safe in cold temps and just ran rich in the summer. like i said this is just what i have read and have been told, thanks for clearning some things up though, i like your answers better lol

Originally Posted by Silverhawk_02TA

Don't worry, not trying to jump on ya or anything. I was under the same impression about SD at first, based on what I'd read in this forum and elsewhere. But after digging deeper and looking at the mass flow calc, and after my own testing, it became apparent that the commonly held conception of SD mode being unable to compensate for temp and pressure changes is just false. No shame in having the wrong impression, we're all learning here, and all most of us have to go on is the available information, which isn't always clear or correct.

One thing to remember: Just because your trims are + or - doesn't mean that your car is running leaner or richer. It's simply the percentage of change to the fueling that the PCM is enacting based on what the O2's are showing. Like in your example, if at 30* the trims are 0 to -1, and at 75* thay are -4 to -5. In both instances, the PCM is maintaining a 14.7:1 AFR. The richness or leaness of the AFR isn't changing, just the percentage that the PCM has to change the mapped fueling based on what the O2's are showing to maintain a 14.7:1 AFR.

Originally Posted by 8KickassRS9

but for most instances the ar isnt truely 14.7, the pcm is jus thinking it, right? i do agree with the air temp should be takin in or very close to the intake. because no matter how good the system some things can be lost in translation and the equation could be off jus enough, ya knw? i would thin SD would be quite sensitive to altitude and radical changes in humidity and air temp. it seems like to make SD work it needs a lot of tricking wht not to control the motor.