sooo lean....why?? Options

[NOMIEZVR4]

i have a logger and my car has always run realll lean and i still havent figured out why. i have a 90 laser with mods in sig, my cat is on right now and my dump is not on the car. my maf is not hacked at all. my fp is not rewired or anything. i need some suggestions as to why my car is running lean. im running 12-13lbs of boost. my logger displays the following:

fuel trim lo 118%
mid 94%
hi 116%
02 volt at WOT .92-.94
timing at WOT 11 degrees(why so low??)
knock maximum 30+ (in 2nd gear around 5k rpms)

if there is anymore info that you need, please ask, i need suggestions, also i run 93 octane.

[natedogg]

Well, your closed-loop trims aren't bad. But you really cant tune by those because once the car goes WOT the ECU switches to open-loop and the trims are ignored by the ECU. You don't seem to me running all that lean to me, but you are running some high knock counts. Go ahead and rewire the fuel pump. That may bring your knock counts down a bit. BTW, your mods never showed up in your sig.

[NOMIEZVR4]

nate, can you please explain the fuel trims open closed loop thing, i wasn't aware of that. so the car only uses the trims when its not at wot??

[NOMIEZVR4]

what should i tune my car by? im getting a s-afc this week, thanks.

[natedogg]

so the car only uses the trims when its not at wot??

Exactly. The fuel trims come from the ECU monitoring the O2 voltage in closed-loop mode. The O2 trim changes constantly with the cycling O2 voltage. Overtime this changes the long term fuel trims. The low trim is for idle and parking lot speeds. The mid trim is for cruising speeds. The high trim is for acceleration but not at WOT. Its called closed-loop mode because the ECU is monitoring feedback from the O2 sensor to tell it how rich or lean the car is actually running. It then adjusts the short-term O2 trim and long-term fuel trims to approach more fuel efficient injector command tables and continues this process as long as the car is running. Trims are there basically to keep the car running at maximum closed-loop power/responsiveness/efficiency in changing weather conditions and driving styles.

Now, open-loop is the mode that the ECU changes to for WOT. It has a set fuel control algorithm based on the airflow signal and possibly the coolant temperature signal. The O2 sensor voltage is ignored which makes sense because it doesn't cycle anymore but stays at a constant voltage near 1 volt. Obviously, it is called open-loop because all feed-back from the O2 sensor is ignored.

There is more info on this stuff at www.tmo.com

what should i tune my car by?

Tune by knock. The knock sensor is the true tell all for how well your car is running. If you are seeing lots of knock you are more than likely running lean at WOT. If you have the new version of the pocketlogger software you can also tune by injector duty cycle. Generally, you want to try to keep the duty cycle at or below 90% at WOT, but if you still see knock at this duty cycle don't be afraid to turn up the fuel some more. You may be able to squeeze a little more fuel out of your injectors yet.

[NOMIEZVR4]

hey nate, do you think the near future, i can stop by and you can help me tune my car?? this freaking knock does not want to go away. i ordered a vr-4 fuel pump and also an afc. do you think i could stop by in a bit i dunno when and we can work things out. thanks, let me know.

[natedogg]

Well, next week is pretty busy for me because I'm closing on a house and moving in. I'll PM you my phone #. Give me a call sometime and we'll work something out possibly for sometime next week, but most likely for sometime in 2 weeks.

You live in Chicago, right? You realize that East Peoria (where I live) is a good 3 hour drive from Chicago. I know there has to be some guys on the Chicago list that live much closer to you that have a logger. You may want to try posting on the ChicagoDSM yahoo groups list. If that doesn't work out for you, feel free to give me a call.

[NOMIEZVR4]

thanks for the info. wow, i never realized how far peoria was from chicago, dayum i will have to rethink this... i have a logger, i just wanted someone with experience to help me out, well, i will see what happens, thanks a lot!!