proper idle afr

[troopercar]

Please excuse me if this is a stupid question. I am tuning a 98 vette. 23x, .59x, 114lsa, ported 243's, 90mmls2 tb, fast 90.

The car runs great, everything is perfect, follows the commanded afr as per wideband.

Here is the issue, at idle it goes nuts and dies at stoich. If I command 15.7 it idles beautifully. The only problem is the stft's keep adding fuel to get it to 14.68 and it starts surging until it dies. This thing otherwise runs perfect but will NOT idle at 14.68. At 15.7afr per the WB it idles awesome. I have tried everything I can think of.

20deg timing at idle, more or less and it gets worse.

I guess the question is can I get it to idle at 15.7afr? If not what needs changed to make it idle at 14.68? Base airflow? Tried that, but I know I have to be missing something.

[troopercar]

Here is the tune. It may seem jacked, I'm trying to sort out someone's tune on a car that has 1000 hands on it.

[WS6FirebirdTA00]

Post a log.

[troopercar]

Post a log.

Too late, I figured it out. Thanks.

[WS6FirebirdTA00]

Posting up information you find is helpful to others who search...

[troopercar]

I forced it into PE at 0-1200rpm and made pe enrichment lean at that same rpm span. Forced it into open loop at idle so I could stay CL everywhere else.

I think this particular heads, cam, intake is giving a false lean at idle and it would adjust itself to death in CL idle.

[SoCal01z28]

I forced it into PE at 0-1200rpm and made pe enrichment lean at that same rpm span. Forced it into open loop at idle so I could stay CL everywhere else.

I think this particular heads, cam, intake is giving a false lean at idle and it would adjust itself to death in CL idle.

how do you force PE mode at idle? just set the delay rpm low? and also how are you setting OL at only idle?

[jimmyblue]

I think you're getting shot-through air bending the WB
reading by excess unburnt air in the pipe.

What I recommend is to find the "happy place" OL AFR
like you did, histo-average the NBO2 voltage and then
work over the switchpoint table to use "what works" as
the target, not 450mV across the board (or whatever).

[gsegse]

I don't think PE will kick even in 0 RPM... you got TPS % Vs RPM

[S2H]

I don't think PE will kick even in 0 RPM... you got TPS % Vs RPM

to get the Idle in open loop you command PE to any value you desire(say 14.7 = 1.0) and you set the TPS to 0..then anything in the rpm ranges you set up will be in open loop...
there are some drawback to it, but most dont experience any issues when they go this route..extremely useful on a large overlap cam that may be idling way rich or way lean but the o2's see it as stoich because of the large overlap in the cam

[gsegse]

got it ......new info

Thanks Boss

[00000D0101]

soundengineer,

It's been a while but I'm positive I read somewhere what years this does and does not work on; do you recall?

Thanks

[S2H]

its worked on all the v8's I have played with...couldnt tell you about any of 4 or 6 cylinder stuff...

[Higgs Boson]

How do you prevent the OLFA table from influencing this? My Commanded AFR is wacked because it is reading from the OLFA table (and the PE table sometimes???).

Does it select the richer of:
Stoich
PE
OLFA

or what? How does this work with regard to OLFA? Setting my PE to 0 seems to put the car in open loop but not necessarily read off the PE table instead of OLFA.

[S2H]

How do you prevent the OLFA table from influencing this? My Commanded AFR is wacked because it is reading from the OLFA table (and the PE table sometimes???).

Does it select the richer of:
Stoich
PE
OLFA

or what? How does this work with regard to OLFA? Setting my PE to 0 seems to put the car in open loop but not necessarily read off the PE table instead of OLFA.

it always reads whichever is Richer(higher commanded EQ value)
so if you want your OLFA to not be used at WOT, set it to a lower value than your PE table

[Higgs Boson]

I tried that and it didn't work. I set pe to .92 and olfa in my idle cells to .81 and it commanded 17.3 and then I tried 1.0 in pe and .92 in olfa and it commanded 13.9.... I don't know what to do!

I have now set my PE and OLFA to 1.0 and will just let it command 14.32 and just ignore the commanded afr. i made a histogram to error from "16" instead of CmndAFR and have the regular AFR Error histogram for the rest of the VE table.

[swebld]

"Reusing" this thread.

I´m using the "PE idle" solution, 1200rpm and under since my O2´s f**** up AFR during CL idle. Works great BUT! Don´t know exactly when it started, and i´m now using 2.23(but can´t really relay this to a 2.23 problem), but when the car is COLD(20 deg C) it´s now commanding 0(zero) "idle desired airflow" .

I´m using RUSS scan config in my scanner. I have to keep the car alive with my throttle pedal for 1 minute since car is commanding ZERO air. Then suddenly car is commanding whatever it needs. Jumps from ZERO to "whatever needed" and car is working perfect - to the next cold start.

Car is ideling at 55kpa varm. Was thinking about the PE Enable MAP or some other parameter preventing the engine to get in to PE mode since MAP is slightly lower during warmup ???

Need some ideas from you guys. What will prevent engine from entering PE mode at idle OR commanding zero air when cold started. Don´t think you need my config ?

[Higgs Boson]

Make sure all your PE delays are zeroed out. You won't hit them at idle and it won't work.

Post your RAF table.

[swebld]

I belive the Corvette is not using any PE delay at all ?
Attached is RAF.

[erics_02_z06]

I tried that and it didn't work. I set pe to .92 and olfa in my idle cells to .81 and it commanded 17.3 and then I tried 1.0 in pe and .92 in olfa and it commanded 13.9.... I don't know what to do!

I have now set my PE and OLFA to 1.0 and will just let it command 14.32 and just ignore the commanded afr. i made a histogram to error from "16" instead of CmndAFR and have the regular AFR Error histogram for the rest of the VE table.

were you able to solve this problem? Right now, I can force open loop by setting the PE TPS % to 0 for the idle cells, but the commanded AFR is always 14.6...so it isnt reading from OLFA or PE for me, but just defaulting to stoich.