BLUEBYU

iTrader: (1)

My last post I indicated the following NA results:

1: O2B1S1/S2 @ WOT = .913 KR=0
LTFT B1/B2 (cells 1-19) = -6.42
2: O2B1S1/S2 @ WOT = .947 KR=0
LTFT B1/B2 (cells 1-19) = -5.13

I proceeded to adjust the base setting 5% lean due to the negative LTFT #'s (left the WOT alone):

1: O2B1S1/S2 @ WOT = .922 KR=0
LTFT B1/B2 (cells 1-19) = +2.13
2: O2B1S1/S2 @ WOT = .915 KR=0
LTFT B1/B2 (cells 1-19) = +2.07

My NOS run came in at prior to MAFT)
1: O2B1S1/S2 @ WOT = .910 KR=0
LTFT B1/B2 (cells 1-19) = -3.68

I did not do a new NOS run until I feel confident with what I am doing. My question is am I on the right track? Is the low positive LTFT #'s (tad lean) better for cruizing? Should I now adjust the WOT to 2% lean to get the O2 #'s down a bit?
With the NOS I think I want to be .89-.9???
Thanks a million for any input!
Randy Hughes
BTW.....Have a great Easter weekend!
OBTW....I set the 4th dip switch to on because I have a GMAF. DO NOT DO THAT THE GMAF IS NOT A 85MM MAF....IT RAN LIKE S##T! AIN'T THIS FUN STUFF! <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

Cool Z

I actually tune my base to achieve a - LTFT avg. Preferably as close to -1 as possible. It seems to make it easier to tune the WOT setting and it stays consistant. Example: my LTFT's avg +5. Base 0 WOT 0 02's .945 all of the time. With Base 0 WOT -2, My WOT 02's would be .925 one run then .945 for another. It would jump around all of the time. It seems (IMHO) to me that with a + LTFT at part throttles, the PCM is sensing the motor is running on the lean side. So at WOT not only is it going into power enrichment, but, it's also adding more fuel to insure the engine does not run lean. Now with the - LTFT, the PCM senses that the engine is actually running alittle an the rich side, and therefore does not add extra fuel during power enrichment. Right now I'm at Base -5 WOT -6. My LTFT avg -3 and WOT 02's .905 almost every time (.905-.915) max timing is 27.5* and 0 KR <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> As far as tuning for the N2O, I would tune the car untill WOT #'s are consistant as originally planned. Then run the 02's at .920ish. That to me is on the slight rich (safe side) to run the N20. I hope this helps you out and good luck <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

<small>[ March 30, 2002, 02:13 AM: Message edited by: cool Z ]</small>

BLUEBYU

iTrader: (1)

I understand the need for consistancy on the O2 readings, but isn't it better to run a bit lean when cruising. The engine would run cleaner with less carbon build-up. BTW, when you indicate -5 on your base setting and -6 on the WOT are you indicating lean settings or rich settings? Thanks for the input Cool Z.
Randy Hughes

Cool Z

I'm sorry it was late and I goofed. My base is +5 (rich) and WOT is -6 (lean). The LTFT is indicating what the computer is doing in real time to achieve stoich (14.7:1) at part throttles. So in essence, when my LTFT's are showing -5.x, it's showing that the PCM is taking out fuel to maintain stoich. The same also works in reverse. IE: +5.x is showing that the PCM is adding fuel to achieve 14.7:1. The PCM always tries to run at stoich at part throttles during light to medium loads. So theoretically, it will not run rich or lean during part throttle as long as the engine is operating within the PCM's ability to correct the rich or lean condition. If it is running to rich or lean, and the PCM cannot compensate for the condition, the computer will set a code and turn on the SES light. I believe the limits for LTFT are +25 and -25. FYI if you would like to really read in depth about all of this, I would recommend a book that I bought about 6 months ago. It really explains to great depth in plain english, and I've learned alot. The title is "How to understand, service and modify Corvette fuel injection & engine management" by Charles O. Probst published by Bentley Publishers (www.Bently Publishers.com) It includes L83, L98, LT1, LT4, LS1, LS6 and LT5 (ZR-1).

BLUEBYU

iTrader: (1)

Cool Z....great info. I am also finding my O2's @ WOT are moving around abit with the LTFT running pretty consistant +2 to +4. I am also getting some KR at random part throttle conditions (none at WOT). That probably is due to higher occurances of lean conditions at cruise. I am going to go the other way with the base setting (i.e. 5% rich) and start the WOT setting @ 2% lean and get some logs. Thanks a million. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
Randy Hughes

Cool Z

Glad I could help. I was trying to make sense of it, and I guess I did. I just expalined it to a friend of mine tonight. His 96 SS is +20 at idle!!! And get this, WOT is .980 <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> !!!! I told him it is time for a MAFT. Take care and feel free to ask for my input anytime. <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" /> Rob