Air/fuel reading questions.
Air/fuel reading questions.
I have had an Apexi Neo on my GS400 for 2 years now. When I first got it I had an intake, exhaust and TM spark plugs. I had it dyno tuned and all was great. I always noticed that while driving normally the Neo would indicate 0; no addition or deletion of A/F mixture. When I would give it WOT the readings would sometimes go up to +7% or +9%; I assume to give more power (and I felt it).
Fast forward another year and I got headers and new O2 seonsors. I then got it re-dyno tuned. Now when I drive normally the Neo still indicates 0 but when I would give it WOT the readings would go DOWN to -5% or -6%.
Why is this? I always thought that adding fuel makes power. Under demanding conditions of WOT I would think the engine needs more fuel...this seems like it is taking it away now. Why is this? Did the previous tuner tune my car wrong the last time?
Fast forward another year and I got headers and new O2 seonsors. I then got it re-dyno tuned. Now when I drive normally the Neo still indicates 0 but when I would give it WOT the readings would go DOWN to -5% or -6%.
Why is this? I always thought that adding fuel makes power. Under demanding conditions of WOT I would think the engine needs more fuel...this seems like it is taking it away now. Why is this? Did the previous tuner tune my car wrong the last time?
Maybe I was unclear. I got my car re-tuned again on a dyno (@ the same dyno shop) after the headers and new O2 sensors were installed. Now at WOT my A/F controller (Apexi Neo) is reading -5% or -6%....which to me would indicate lessening fuel but why would this be under the demand of WOT? Before, under WOT conditions my controller would display +7, +8 or +9% indicating it was adding fuel for the extra demand. I am not sure why I am in the negatives now.
I hope he tuned it right.
Are you sure you aren't remembering incorrectly? The AFC can't automatically adjust itself, if you set it for 5-6% then that's where its set and nothing will change that unless someone goes in a physically adjusts it with the buttons on the AFC. It will also have a different amount of adjustment for different rpm points so you need to compare the same rpm points on all runs, you may have -6% at one point and +6% at another point.
Another thing to consider is temperature and humidity at the time of the dyno. If it was cold out when you dynoed the first time the car was probably getting air that was more dense with oxygen. Due to the greater amount of oxygen their would be a requirement for more fuel to match it. If it was a hot/humid day there would be less oxygen in the air, this would need less fuel. Also, if your old oxygen sensors were bad the car may have readjusted the tuning based on the O2 readings, maybe it was running rich on old O2 sensors and once you replaced them it leaned out due to a more accurate reading.
Also, you typically make more power by leaning the car out, generally cars will make more power the leaner you go. The key is finding the fine line of max power while still being safe (not too lean).
Another thing to consider is temperature and humidity at the time of the dyno. If it was cold out when you dynoed the first time the car was probably getting air that was more dense with oxygen. Due to the greater amount of oxygen their would be a requirement for more fuel to match it. If it was a hot/humid day there would be less oxygen in the air, this would need less fuel. Also, if your old oxygen sensors were bad the car may have readjusted the tuning based on the O2 readings, maybe it was running rich on old O2 sensors and once you replaced them it leaned out due to a more accurate reading.
Also, you typically make more power by leaning the car out, generally cars will make more power the leaner you go. The key is finding the fine line of max power while still being safe (not too lean).
Last edited by macd7919; Jul 23, 2009 at 12:30 PM.
Are you sure you aren't remembering incorrectly? The AFC can't automatically adjust itself, if you set it for 5-6% then that's where its set and nothing will change that unless someone goes in a physically adjusts it with the buttons on the AFC. It will also have a different amount of adjustment for different rpm points so you need to compare the same rpm points on all runs, you may have -6% at one point and +6% at another point.
Another thing to consider is temperature and humidity at the time of the dyno. If it was cold out when you dynoed the first time the car was probably getting air that was more dense with oxygen. Due to the greater amount of oxygen their would be a requirement for more fuel to match it. If it was a hot/humid day there would be less oxygen in the air, this would need less fuel. Also, if your old oxygen sensors were bad the car may have readjusted the tuning based on the O2 readings, maybe it was running rich on old O2 sensors and once you replaced them it leaned out due to a more accurate reading.
Also, you typically make more power by leaning the car out, generally cars will make more power the leaner you go. The key is finding the fine line of max power while still being safe (not too lean).
Another thing to consider is temperature and humidity at the time of the dyno. If it was cold out when you dynoed the first time the car was probably getting air that was more dense with oxygen. Due to the greater amount of oxygen their would be a requirement for more fuel to match it. If it was a hot/humid day there would be less oxygen in the air, this would need less fuel. Also, if your old oxygen sensors were bad the car may have readjusted the tuning based on the O2 readings, maybe it was running rich on old O2 sensors and once you replaced them it leaned out due to a more accurate reading.
Also, you typically make more power by leaning the car out, generally cars will make more power the leaner you go. The key is finding the fine line of max power while still being safe (not too lean).
ahhh, got it. Just for your information the reason why it was +7%, +8% or +9% at WOT was that is how the tuner adjusted it a while back. Then the tuner re-adjusted it again on the dyno more recently (after I replaced the O2's and added headers). Since the most recent dyno the neo is reading into the negatives at WOT where I thought he tuned it incorrectly but I see your point now.
Forgive my ignorance when it comes to this tuning stuff but leaning out meaning less fuel, correct?
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