i have a 383 lt1 with a 250 256 dur@50 solid roller. it has 76 deg. of overlap. im also running dfi. so i know i cant idle in closed loop but can run the o2 above idle. my idle seems to rich,and when it goes in to closed loop at about 1500rpm the o2 tries to pull a ton of fuel like 12% but i dont think the idle is that rich,maybe time to ditch the dfi o2 all together as the car hiccups when this hapens. it was tuned on a dyno with a wideband,but in open loop, and i also have a in car wideband. it reads lean of course, but the dfi o2 and the wide band o2 dont read the same. kinda wierd, one is on each side of the motor,but cant be that different bank to bank.

so my ? is, whats the best way to set my AFR at idle since the 02's aren't reading the right mixture at idle? anybody know or how to figure out what a reading would be with the wideband? lets say, i want a 13.5 AFR at idle, is there a fudge factor to what the wide band is reading,i think im reading like 15.5 AFR on the WB. my MAP is in the low 70's ,vacuum is about 10inches, and my timing is 30 deg. thanks for any help, jay

 

Tune the at idle fuel with a vaccum gauge. Just like a carb.

Rember tuning is not giving the car a certain number AFR but what it wants.

 

Not wierd, one is DEFINITELY not displaying accurate numbers. Remember though, unburned fuel will show up on a WB O2 meter as lean, as it measures the oxygen content of the exhaust. Forget the fudge factor, get (or make sure you have) an accurate recording WB O2 controller/meter. What WB O2 unit are you presently using? Also, it would NOT be the first time a dyno WB unit was inaccurate. They should not automatically, be considered accurate, or FTM, be considered the last word in accuracy.

 

I have a 260/260 @ .050 solid roller and a wideband.

#1 the idle will ALWAYS be rich, its going to stink and theres no way to fix it because hte cam is so big.

#2 however there is a way to HELP it be tolerable. First off, we both know the AFR is not read correctly at idle. But you can still use hte wideband to bring it inline.

#3-----MY car idles at 1000-1100 and with it tuned properly and runinng real good my wideband reads between 18:1-19:1 AFR. now this isnt the ACTUAL AFR, but "untechnically" this is a fudge factor you can use. Set up your DFI wideband to aim for 18:1 at closed loop idle. IF the DFI still wants to add fuel you might have to severely limit or even disable its fuel trims at idle. I sold my DFI 7 but I am pretty sure there are alot more settings for idle then the stock PCM.

 

first im useing the dynojet wideband commander (www.widebandcommander.com) its basically another version WB with the bosch wideband o2. i also have the older gen 6 dfi with the standard (not wideband) o2. i wouldnt be suprised if the original dyno WB that i tuned with was off, it was a dynojet,but a tailpipe sensor not a o2. but the 02 in the dfi says the car is rich,where the WB says its lean. im going by voltage (.700) with the dfi sensor. the wideband is new, and the dfi o2 is about a year old, but the car was run rich for awhile while trying to sort this out with the dfi o2,so maybe its ruined from running rich alot.

tripintaz,
ive trieed to idle my car that way, with the WB reading 18:1 AFR, but it was lean, and would pop and miss at any hit of the throttle.it seems to be happy at 15:1 but seems rich to me. i know it will always smell rich,but id like to make it more tollerable.
since your cam is bigger, id say the overlap is higher, wich would let more air into the exhaust making your WB read different from mine.

im gonna try playing with the vaccum gauge and see what i come up with.
thanksguys, jay

 

Have you tried rasing the idle timing? Try 27-34 and see if that helps. Big cams need more timing, at least at idle.

 

I use 40 degrees of timing at idle. Increasing my idle timing definatly helped the richness factor and made the car idle better. Also you should be idling about 1000 RPM.