Question about O2 behavior in OL/CL
Question about O2 behavior in OL/CL Still relatively new to tuning and have a question about O2 behavior. In closed loop I know the O2's oscillate (not real sure why) and the average should be around stoichiometric. Once I go open loop w/ PE the O2 readings jump up and stay around 880-920 mV (which I know is a good thing being closer to 12.8-13.0:1). My question is why the O2 output is different for closed vs. open loop. I'm just trying to improve my understanding as I'm currently tuning VE tables in SD. I disabled PE and DFCO for the logging. Thanks for the help.
TECH Senior Member
Joined: Nov 2001
Posts: 7,036
Likes: 1
From: Lake Zurich, IL
because the O2s are only accurate in Closed loop (or at 14.7:1... stoich) ... in PE you're dumping alot more fuel so the O2s no longer oscillate since the PCM doesn't use them to control fueling at that point...
The reason they oscillate is that the PCM is constantly adjusting the fueling to maintain an average of 14.7:1 ... so the PCM is constantly adding and removing fuel which results in high low high low oscillation ... at WOT you're just dumping fuel in without removing any... thus no oscillation
and 880-920 doesn't necessarily mean it's closer to 12.8-13.0 ... 880 is a little lean for my tastes (for narrowband tuning) ... but there really isn't much correlation between an AFR and a O2 voltage output (narrowband are only accurate for a very narrow range of AFRs)
And... not a good idea to disable PE (Since you seem to be doing SD tuning w/out a wideband... you can only safely tune lower RPM lower loads...) ..... 14.7:1 at high load is a good way to blow your motor up... high load high RPM SD tuning simply can't be done safely and accurately with a narrowband sensor... Part throttle driveability can be tuned safely and accurately but once you get to higher loads and RPMs... 14.7:1 AFR is NOT a good thing...
I would turn PE back on or avoid high load or high RPM... unless you enjoy detonation...
The reason they oscillate is that the PCM is constantly adjusting the fueling to maintain an average of 14.7:1 ... so the PCM is constantly adding and removing fuel which results in high low high low oscillation ... at WOT you're just dumping fuel in without removing any... thus no oscillation
and 880-920 doesn't necessarily mean it's closer to 12.8-13.0 ... 880 is a little lean for my tastes (for narrowband tuning) ... but there really isn't much correlation between an AFR and a O2 voltage output (narrowband are only accurate for a very narrow range of AFRs)
And... not a good idea to disable PE (Since you seem to be doing SD tuning w/out a wideband... you can only safely tune lower RPM lower loads...) ..... 14.7:1 at high load is a good way to blow your motor up... high load high RPM SD tuning simply can't be done safely and accurately with a narrowband sensor... Part throttle driveability can be tuned safely and accurately but once you get to higher loads and RPMs... 14.7:1 AFR is NOT a good thing...
I would turn PE back on or avoid high load or high RPM... unless you enjoy detonation...
Well before I realized that I had my OLF/A table values at 1.0 I did log some runs at high rpm w/ PE disabled. I reenabled it earlier today and made sure I was in the 880-920 mV range. Another rookie mistake on my part but at least it was only lean for a few high rpms runs by me today. I definitely want a wideband but I can't stand having to pay another $150 for the damn interface. On the other hand $3K for a new shortblock is a LOT more money!
edit - quick question about when I had PE disabled earlier...if it did start detonating would I get some KR for a little protection or not?
edit - quick question about when I had PE disabled earlier...if it did start detonating would I get some KR for a little protection or not?
