STFT negative after dialing in VE/MAF
05-25-2016, 10:05 AM
#1
STFT negative after dialing in VE/MAF I've tuned my VE and MAF tables to within 1-2% error, then enabled closed loop (LTFTs off) and did some logging. Each time my STFT are showing negative 4-8 in the 4000 and lower cruise type driving I'm doing. Actual AFR around 15.1 in this range where as in open loop having tuned VE/MAF my AFR was much closer to 14.7 most of the time. After logging in closed loop a few times I would make some small changes to MAF and VE but my STFTs want to stay negative and by adding fuel it seems the STFTs are going increasingly negative each time.
LS1, LS6 intake, PRC 225 heads, TSP Torquer v2 cam, stock maf, long tube 1 7/8 headers. O2 sensors just after the collectors.
Is what I'm seeing with the STFTs due to the location of the O2s and the cam? Are there some adjustments that can be made to prevent the O2s from making the PCM think its rich and subtract fuel? I suppose 15.1 AFR is not bad for lean cruise.. should I just leave it there and make sure I get correct AFR in PE/WOT? I'll attach my last log and tune.
LS1, LS6 intake, PRC 225 heads, TSP Torquer v2 cam, stock maf, long tube 1 7/8 headers. O2 sensors just after the collectors.
Is what I'm seeing with the STFTs due to the location of the O2s and the cam? Are there some adjustments that can be made to prevent the O2s from making the PCM think its rich and subtract fuel? I suppose 15.1 AFR is not bad for lean cruise.. should I just leave it there and make sure I get correct AFR in PE/WOT? I'll attach my last log and tune.
05-25-2016, 11:36 AM
#2
I think I found a answer... Guessing I need to get the o2s to agree with the wideband on what stoich is. I think I will run a couple more logs to recheck VE and MAF, make sure I'm good there and then work through the O2 switchpoints/airflow mode as talked about here.
http://www.hptuners.com/forum/showth...ts-to-Match-WB
http://www.hptuners.com/forum/showth...ts-to-Match-WB
05-31-2016, 10:32 AM
#3
After researching a bit more I'm not quite clear what direction to take. Anyone else been down this path tuning closed loop AFR with Long tubes?
Basically I'm not sure if the plan of attack should be to adjust the O2 switchpoints or if adjusting the table(s) that account for the transport delay should be adjusted first? I'm no expert by any means but it appears the o2s are oscillating nicely its just that being farther away from the head than in a stock configuration they are potentially colder, being effected by the cam and thus reading differently. On the surface adjusting the switchpoints seems like the quick fix but maybe thats masking the real issue and would create others?
When my wideband says i'm running 14.7 at steady cruise, the O2s are around 800 so the computer thinks its rich and consistently pulls out fuel.
I may just go openloop and forget it but figured it couldn't hurt to play around with this as time allows.
Basically I'm not sure if the plan of attack should be to adjust the O2 switchpoints or if adjusting the table(s) that account for the transport delay should be adjusted first? I'm no expert by any means but it appears the o2s are oscillating nicely its just that being farther away from the head than in a stock configuration they are potentially colder, being effected by the cam and thus reading differently. On the surface adjusting the switchpoints seems like the quick fix but maybe thats masking the real issue and would create others?
When my wideband says i'm running 14.7 at steady cruise, the O2s are around 800 so the computer thinks its rich and consistently pulls out fuel.
I may just go openloop and forget it but figured it couldn't hurt to play around with this as time allows.