Air fuel and auto tap
Air fuel and auto tap Is the calculation on autotap correct(fairly accurate). My o'2 read good(don't have wide band)but a/f ratio says 11.8.The car still blows black smoke like it is rich but if I lean it out anymore it drops hp and runs worse. Opinions please.
Re: Air fuel and auto tap I found A-tap can give false readings because the 02's are not very accurate.
When I dyno'd with wideband A/F stayed around 12.8-1 on 4 runs.My atap showed different on each run.as low as .820v to as high as .98v.A good thing to go by is knock retard.If it goes too lean it will pull timing.
When I dyno'd with wideband A/F stayed around 12.8-1 on 4 runs.My atap showed different on each run.as low as .820v to as high as .98v.A good thing to go by is knock retard.If it goes too lean it will pull timing.
TECH Addict
Joined: Nov 2001
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From: College Station, Tx
Re: Air fuel and auto tap The a/f paramter on autotap is not derived from the o2's - they are a narrow band type sensor, so a valid extrapolation is not possible with the data at hand.
Rather, the value is a calculated value based on the air massflow and injector massflow. It is the a/f ratio the computer is commanding essentially.
Chris
Rather, the value is a calculated value based on the air massflow and injector massflow. It is the a/f ratio the computer is commanding essentially.
Chris
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From: Chicagoland
Re: Air fuel and auto tap I'm not sure of the code in the LS1's, and I'm not sure anyone on the board is either, but on older GM ECM's, they had tables that would do a lookup for the 'desired' AFR based on coolant/RPM/airflow or manifold pressure. At startup you might need 10:1, at warmed up idle you'd want 14.7:1. At WOT/PE mode, you'd want 12:1. Many of the older ECM's used these as fueling multipliers in the fueling algorithsm. Anyways, they aren't a sensor value at all.
I believe to say that it is commanding that AFR is in err as well, because a commanded AFR would be one that the computer is correcting short term fueling values to manipulate the actual AFR to agree with the commanded AFR. The factory computer cannot target any AFR but 14.7:1. LS6 PCM's have different code that is closed loop at WOT, but is still sketchy as far as I know. I'd call that value more of an ideal or desired AFR value.
Brian Green
89 TTA
couple different LS1 projects
I believe to say that it is commanding that AFR is in err as well, because a commanded AFR would be one that the computer is correcting short term fueling values to manipulate the actual AFR to agree with the commanded AFR. The factory computer cannot target any AFR but 14.7:1. LS6 PCM's have different code that is closed loop at WOT, but is still sketchy as far as I know. I'd call that value more of an ideal or desired AFR value.
Brian Green
89 TTA
couple different LS1 projects
TECH Addict
Joined: Nov 2001
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From: College Station, Tx
Re: Air fuel and auto tap In the LS1 computer the value can be derived in reverse using injector flow and MAF flow - if you copy the injector flow table, log injector pw, MAP (to reference vs. the injector flow table), and MAF you can calculate the A/F ratio parameter in reverse - log all of the above and check it out for yourself.
If you want to call this desired, commanded, whatever - that's just a matter of semantics. Since the value is derived (apparently) from the BPW, s-trims, l-trims, etc. will already be included in the figuring.
In the end it is the ratio of airflow to injector flow.
Chris
If you want to call this desired, commanded, whatever - that's just a matter of semantics. Since the value is derived (apparently) from the BPW, s-trims, l-trims, etc. will already be included in the figuring.
In the end it is the ratio of airflow to injector flow.
Chris
On The Tree
Joined: Feb 2002
Posts: 188
Likes: 0
From: Chicagoland
Re: Air fuel and auto tap In the LS1 computer the value can be derived in reverse using injector flow and MAF flow - if you copy the injector flow table, log injector pw, MAP (to reference vs. the injector flow table), and MAF you can calculate the A/F ratio parameter in reverse - log all of the above and check it out for yourself.
If you want to call this desired, commanded, whatever - that's just a matter of semantics. Since the value is derived (apparently) from the BPW, s-trims, l-trims, etc. will already be included in the figuring.
In the end it is the ratio of airflow to injector flow.
I've seen shops that actually have used MAF sensors and such to estimate AFR's. I found it amusing..
Thanks for the clarification Chris.
I'm curious, does Autotap do these calcs, or are they done by the GM computer and spit out in the serial data?
Brian Green
89 TTA
couple different LS1 projects
If you want to call this desired, commanded, whatever - that's just a matter of semantics. Since the value is derived (apparently) from the BPW, s-trims, l-trims, etc. will already be included in the figuring.
In the end it is the ratio of airflow to injector flow.
I've seen shops that actually have used MAF sensors and such to estimate AFR's. I found it amusing..
Thanks for the clarification Chris.
I'm curious, does Autotap do these calcs, or are they done by the GM computer and spit out in the serial data?
Brian Green
89 TTA
couple different LS1 projects
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Re: Air fuel and auto tap </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif"> I really don't know if autotap does them or if they are in the GM data stream - I would guess the latter though.
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">ChrisB's guess is correct - the AFR is in the data stream.
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">ChrisB's guess is correct - the AFR is in the data stream.
