95 trans am lt1 diagnosing poor running/ running lean

[zoomo]

so even with the maf unplugged, the 02 sensor still effects the fuel trim? i was under the assumption that with the maf unplugged it would run off of the ve table. but then again taht may not be correct ha. anyway new 02 installed. drove a little seems to do a lot better. much more driveable now, i think i may have still heard it pop a couple times under acceleration. and also still the power seems low and drops off around 4000 rpm and higher. though i know the timing definetly seems high at around 40 at 4000 rpm although it doesnt seem to be retarding the timing? before the 02 sensor change, the car was nearly undrivable it would bog and miss badly anytime you tried to hold steady throttle. anyway heres some more logs

[steveo]

that's not quite how it works.

with the maf unplugged you're correct that it uses VE tables... but closed loop is an additional fueling calculation on top of either one of those.

i wrote this a while ago might clear it up for you http://fbodytech.com/tuning.html#modes

will look at your logs soon

[steveo]

in the cruising log, it doesn't even seem to make it into closed loop for some reason, but the highway one seems not too bad. your timing advance needs a bit of love (mostly due to the different cam) but it's a good start.

you should lay off the 100% throttle until it's tuned.

breaking up at high rpm might be due to the fact that someone leaned out your PE tables quite a bit. try this bin instead. i tweaked your timing table a bit too to get it closer, and a few other small things, but it still needs work.

[zoomo]

Thanks so much steveo. the cruising was actually right as i left the house. i should have clarified that, and i went to highway within about 7 minutes of driving so it may have just been getting warmed up i read you link and its very informative, though i will need to read it a few more times ha. going out to install your bin shortly. thanks again for the help and ill post the results

[zoomo]

well i went for a good long drive today. it does a lot better. seems to bog under load/cruising situations. almost feels like it starts to miss fire. is it possible im missing something here? is it possible im actually getting a missfire from a failing injector or some sort of wierd ignition misfire that we cant see in the logs well? (dont get me wrong i have checked for both these conditions very well and the injectors resistance test good, visual check and spray looks good, ignition wires are new although cheap and optispark is new from chandlermotorsports? ebay shit i know, but ive removed and inspected it and seems to be working well.)

Anyways thanks for all the help so far steve. I did not realize that i had actually found your sites in all my searching and i was already using your ee file. im very interested in learning and understanding tuning this way. i work on cars as my "career" and have a very good understanding of tuning a car, and tune a carb and a distributor. I also do a lot of laptop-based scanning/diagnostic/programming on customer cars, but everything i do is back to factory. so this is very new to me, but im starting to get a decent understanding of it i feel. and im very thankful i came across this forum, and you to hopefully help me get a better understanding. thanks again to everyone. ok so heres some log files, let me know what you think. once again thanks for everything.




EDIT: back again, looking at the way its bogging and popping occasionally at low rpm cruise/acceleration. wondering about the timing being too high in those situations so i was just playing with the timing curve, like i said im used to turning a distributor so its very linear, let me know if im completely out of line. thanks again

EDIT2: check the second linear timing edit, more what im thinking. also adjusted corrcl. will let you know how it works. please feel free to give me advice im doing lots of searching ha

[steveo]

my timing table is a guess i've never tuned for this particular cam before.

EFI and distributors can be tuned nearly the same way, just think of your RPM rows as your base timing vs your final timing, and the curve to get there. then your MAP columns are vacuum advance on top of that.

if you made a graph of timing advance at various points of a well-designed vac advance distributor setup, it'd look kinda similar to an efi timing table.

i did look at your timing table, it's a bit cracked out for sure.

think of it this way, that cam under 40kpa will always be decellerating. so all your 'vacuum advance' only comes in on decel, except for below 1600rpm under low loads, which is way out of operating range.

look how your 50-55 map row (which i'd guess is cruising range) advances the hell out of timing up to 38 degrees, and then drop s back to 32? in driving ranges, timing should never have to decrease substantially with rpm, just level off.

lets express this a different way so you can learn about timing, if this was a distributor, how would you tune initial, final, and vacuum advance?

[zoomo]

ah i see what youre saying, how i missed that i dont know. thats basically what i was trying to do, just set the timing curve like a distributor. where as you just set your initial, maybe some added timing by vacuum advance at idle ( sometimes dont run vacuum advance depending on cam) and then you just set the timing curve to extend up to 28-38 topping out at around 3000 rpm. of course then you have the option of adding more advance at cruise with the vacuum advance. this seems to help with gas mileage. i know thats very basic and im sure you understand, and know this, but thats what i was trying to accomplish. im going to adjust the part at high vacuum at cruise. i suppose really i was thinking that was would be at idle, but i see now that i could reach those conditions at cruising as well. i think i asked already, and i know ive searched but is there any way in hell i could be missing some kind of missfire under this load/cruise/acceleration, one that was caused by something other than just the tune? when you cruise it starts to shake, feels almost like its missing, but the sound is smooth. thanks again for everything steve, i dont mean to be needy, i am doing searching i promise, its just hard to narrow things down sometimes.

[steveo]

disconnecting vacuum advance for a radical cam is always done because the vacuum advance canister can't be configured properly for the cam. in this case, you have infinite control, so not having vac advance would be silly, unless its a racecar or something and you just don't care.

you could definitely have a misfire or other problem unrelated to the tune.

i would expect the timing map i made you to have a bit of 'surge' or feel a bit weird in some areas, again, because im unfamiliar with the cam, but it shouldn't really 'bog down' or stutter or anything.