CenWaSS Posted March 23, 2009 Report Share Posted March 23, 2009 Just curious (cause Im new to this FI), but where should my A/F ratio be? Under normal driving my guage reads 14.9 to 14.5 plus or minus a tenth either way. Under WOT and 6lbs of boost my A/F reading drops to 10.0 Do those readings sound ok? Quote Link to comment Share on other sites More sharing options...
Krambo Posted March 23, 2009 Report Share Posted March 23, 2009 (edited) A little rich IMHO at WOT. I look to have an AFR of around 11.75 for FI when in Pe mode (WOT). Your cruising readings appear to be normal. Do you have anyway to monitor your LTFT's? BTW, alot of wideband gauges only read to 10.0 so you may be going more rich than what you read. Edited March 23, 2009 by Krambo (see edit history) Quote Link to comment Share on other sites More sharing options...
got vortec Posted March 23, 2009 Report Share Posted March 23, 2009 if yer running rich under wot...add sum spray..lol itll fix it Quote Link to comment Share on other sites More sharing options...
silverado_ss_04 Posted March 23, 2009 Report Share Posted March 23, 2009 Quote Link to comment Share on other sites More sharing options...
brobradh77 Posted March 23, 2009 Report Share Posted March 23, 2009 i'm at about 10.8 ish now but i'm hoping to get that corrected. Quote Link to comment Share on other sites More sharing options...
CenWaSS Posted March 23, 2009 Author Report Share Posted March 23, 2009 A little rich IMHO at WOT. I look to have an AFR of around 11.75 for FI when in Pe mode (WOT). Your cruising readings appear to be normal. Do you have anyway to monitor your LTFT's? BTW, alot of wideband gauges only read to 10.0 so you may be going more rich than what you read. Thanks for the info. I do not have a way to monitor LTFT's (not exactly sure what that is?). My tuner mentioned he was sending out a leaner tune. Quote Link to comment Share on other sites More sharing options...
SSThunder Posted March 24, 2009 Report Share Posted March 24, 2009 ok. so the higher the number the leaner you are? I've finally got my gauge working correct so I'm seeing decent number at idle. I haven't had a WOT run yet. Quote Link to comment Share on other sites More sharing options...
brobradh77 Posted March 24, 2009 Report Share Posted March 24, 2009 ok. so the higher the number the leaner you are? I've finally got my gauge working correct so I'm seeing decent number at idle. I haven't had a WOT run yet. Yes and you want to be 11's mid or so...If you see 12 you need to get out of it. Quote Link to comment Share on other sites More sharing options...
SSThunder Posted March 24, 2009 Report Share Posted March 24, 2009 Yes and you want to be 11's mid or so...If you see 12 you need to get out of it. Ok. thanks. I've got a quick question. I've got my wideband hooked up in my rear O2 located behind the dynatech cat. Will that have any effect on my readings? I assume not since my readings are 14.6 or 14.7 at idle. Quote Link to comment Share on other sites More sharing options...
brobradh77 Posted March 24, 2009 Report Share Posted March 24, 2009 Ok. thanks. I've got a quick question. I've got my wideband hooked up in my rear O2 located behind the dynatech cat. Will that have any effect on my readings? I assume not since my readings are 14.6 or 14.7 at idle. i wouldnt think so Quote Link to comment Share on other sites More sharing options...
BigCountry Posted March 24, 2009 Report Share Posted March 24, 2009 You want your sensor before the cat to be accurate. May make quite a difference...... I think you need to add more boost, that'll lean it out Quote Link to comment Share on other sites More sharing options...
SRT10KLLR Posted March 24, 2009 Report Share Posted March 24, 2009 A little rich IMHO at WOT. I look to have an AFR of around 11.75 for FI when in Pe mode (WOT). Your cruising readings appear to be normal. Do you have anyway to monitor your LTFT's? BTW, alot of wideband gauges only read to 10.0 so you may be going more rich than what you read. You are just a tad rich at WOT but good at idle/cruise. But like others have said just up the boost, lol. BTW, LTFT means Long Term Fuel Trim. The PCM records all the data as far as how much it adds/subtracts to get you a/f as close to 14.7 as possible when in closed loop(idle/cruise) but ignores your O2 sensors at WOT. Quote Link to comment Share on other sites More sharing options...
Krambo Posted March 24, 2009 Report Share Posted March 24, 2009 (edited) As SRT10KLLR stated, monitoring your Fuel Trims is a way to see if your PCM is adding or subtracting fuel to get you to your commanded STOICH (14.68 for typical pump gas) during cruise and part throttle (non Pe mode). If your fuel trims are "+" your PCM is adding fuel to correct for a lean condition and if the fuel trims are "-" the PCM is pulling fuel to compensate for a rich condition. (Rich = numarically Lower than Stoich, (Lean = numarically Higher than Stoich, >14.68) Typical trims on a stock tune will vary and it isn't a cause for alarm unless they are way out. Varying weather conditions, altitude, ethanol content in your fuel, bolt-on mods etc. will all impact your trims. The way to correct wide ranging LTFT's is tuning your Ve table of which you will probably hear tuners talking about. A well dialed in Ve table will show 0 to -3 for the LTFT's and takes time to get there. I have seen stock brand new trucks with +/- 7 on the LTFT's. Now if your fuel trims are "+", your PCM will dump that extra number (understood by the PCM as a %) on top of your WOT (Pe) commanded AFR. So if your LTFT's are +7 and you command say a 12.0 in WOT, the PCM will add 7% on top of that 12.0 to richen up the mixture. It is kind of a safety thing that is programmed into the logic of the PCM when using the stock Operating System. I prefer to tune my trims on the negative side (rich). Monitoring your Fuel Trims is also a good way to diagnose post MAF air leaks or Exhaust leaks (pre front O2 sensors). Way positive fuel trims indicate that the PCM is dumping alot of fuel to compensate for a perceived lean condition. So if your LTFT's are say +22...start looking for air / exhaust leaks. There are also STFT (short term fuel trims) but for all case in purpose, ignore them or you will go nuts. Edited March 25, 2009 by Krambo (see edit history) Quote Link to comment Share on other sites More sharing options...
CenWaSS Posted March 24, 2009 Author Report Share Posted March 24, 2009 Wow! good info Very informative, Thanks! Quote Link to comment Share on other sites More sharing options...
SRT10KLLR Posted March 25, 2009 Report Share Posted March 25, 2009 As SRT10KLLR stated, monitoring your Fuel Trims is a way to see if your PCM is adding or subtracting fuel to get you to your commanded STOICH (14.68 for typical pump gas) during cruise and part throttle (non Pe mode). If your fuel trims are "+" your PCM is adding fuel to correct for a lean condition (numarically lower than STOICH, <14.68) and if the fuel trims are "-" the PCM is pulling fuel to compensate for a rich condition (numarically higher than Stoich, >14.68). Typical trims on a stock tune will vary and it isn't a cause for alarm unless they are way out. Varying weather conditions, altitude, ethanol content in your fuel, bolt-on mods etc. will all impact your trims. The way to correct wide ranging LTFT's is tuning your Ve table of which you will probably hear tuners talking about. A well dialed in Ve table will show 0 to -3 for the LTFT's and takes time to get there. I have seen stock brand new trucks with +/- 7 on the LTFT's. Now if your fuel trims are "+", your PCM will dump that extra number (understood by the PCM as a %) on top of your WOT (Pe) commanded AFR. So if your LTFT's are +7 and you command say a 12.0 in WOT, the PCM will add 7% on top of that 12.0 to richen up the mixture. It is kind of a safety thing that is programmed into the logic of the PCM when using the stock Operating System. I prefer to tune my trims on the negative side (rich). Monitoring your Fuel Trims is also a good way to diagnose post MAF air leaks or Exhaust leaks (pre front O2 sensors). Way positive fuel trims indicate that the PCM is dumping alot of fuel to compensate for a perceived lean condition. So if your LTFT's are say +22...start looking for air / exhaust leaks. There are also STFT (short term fuel trims) but for all case in purpose, ignore them or you will go nuts. Krambo, I am not sure if I read your post correctly but it sounds like you have it backwards. A richer A/F is numerically lower than stoich ie. if you are runing an A/F of 10:1 then you are rich and thus numerically lower than 14.68(stoich). A leaner A/F is numerically higher than stoich ie. if you are runing an A/F of 17:1 then you are lean and thus numerically higher than 14.68(stoich). Quote Link to comment Share on other sites More sharing options...
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