adjusting fuel for gearing...

[David Cooley]

Most PCM's/ECM's have a table for PE vs TIME.  IE: the longer the throttle 
is held to the floor, the more fuel is added.  An O2 number isn't a good 
way to tune.  O2 volts depends on mixture, but they also vary by EGT, 
distance from the cylinder etc.  I learned that when tuning a 3800 
V6.  Trying to get my O2 down to .850 (Which I had heard was a good number) 
when I got below .875, I got surging and detonation...  On a buick Grand 
national, .875 was "pig rich" and .800 was the target...  Best measure is 
time  (performance... 0-60, 0-100 or 1/4 mile runs) and plug cuts, but 
*ALWAYS* keeping an eye on detonation.  Pretty easy to go too lean and hole 
a piston!.


At 10:24 AM 4/16/00, you wrote:
>Hey guys this is what i got.
>
>these readings are at WOT from diacom.
>
>1st gear 4175 02 reads .876
>2nd gear 4250 02 reads .894
>3rd gear 4225 02 reads .942
>
>How the hell do i adjust the fuel curve?
>
>1st and second are good but third is way rich.. all i can do is 
>add-subtract fuel by rpm, can't do anything for gearing....
>
>those readings are taken off the same run.
>
>at 4650 in 3rd i was at .956 02 voltage!!!
>but at 5650 in 2nd i was at .916! (same run)
>
>trying to get a good curve of .9 all the way but 1st is always leaner than 
>second, and second is always leaner than third...
>
>should i tune for 900 at second and let 1st be a tad lean and third rich 
>or what?
>
>thanks,
>Shane

===========================================================
David Cooley N5XMT Internet: N5XMT at bellsouth.net
Packet: N5XMT at KQ4LO.#INT.NC.USA.NA T.A.P.R. Member #7068
We are Borg... Prepare to be assimilated!
===========================================================

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org