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Yes... All that is believable. It isn't using it for trimming the fuel that is shown in your STFT and LTFT which is what your post is about
It is using it to take care of the CAT. They failed to mention they trim for cat over temp protection.
Now if you want your LTFT and STFT to look this good at highway speeds... Try listening to someone rather than going off on a Google said tantrum.
Well... it is a big deal to you or you wouldn't be asking what's wrong with yours. You can either choose to listen or not what people tell you. Based on your past posts, you won't listen.
i asked a simple question about no cat and factory programming with LTFT and rear o2 and you post stuff that only applies pre 1999, but some GM engineer told you, even though the GM odb2 manual says they use the rear o2 for fuel trim.
The rear O2 after the cat warms up has a steady voltage if the Cat is doing it's job. I unplugged mine and turned off my Post O2 diagnostics... No light and still a perfect ST & LT fuel trim.
You guys are both right. The rear has very little, if any, authority to command fuel trims in our engine. That's why when ppl go catless they usually unplug the rear and turn off the MIL. Either your ECU is incrementing the LTFT up to +8 because of the lack of a cat, or there's a different issue. The answer is to unplug and command the MIL off, and since you don't have access to HPT I would suggest to just unplug it and see if it goes away. If it doesn't, then there's something else causing it.
teh stft and ltft are high because its a GM stg 2 tune and a AEM intake & cone filter and LT header w/o cat has been added further skewing.
i was just curious if i would be better off with the CEL and rear o2 unplugged or letting it sit in there and and adjust my fuel incorrectly overtime..
solution is always custom programming
HGT always gotta chime in about his project while posting half truths
The answer is that it's very likely not adjusting your trims. You can find out by unplugging. Regardless your concern should be solving the trims, not worrying about the rear O2 sensor. It's a red herring and can be completely resolved by unplugging for now. I still think something is off since it should be sending a MIL for a non-functioning cat.
If you haven't tuned after adding that intake guaranteed that's your issue. If you don't have emissions testing, it doesn't matter whether it's plugged or not. If you do, you need to tune out the code (for big brother's sake, i'm not advocating this).
The answer is that it's very likely not adjusting your trims. You can find out by unplugging. Regardless your concern should be solving the trims, not worrying about the rear O2 sensor. It's a red herring and can be completely resolved by unplugging for now. I still think something is off since it should be sending a MIL for a non-functioning cat.
its occasionally does throw the out of range code, and sometimes the o2 heater control circuit code. but not very often like it can go weeks or a month or longer without throwing the code.
i might try to unplugg the rear o2 and watch the trims and see if they stay the same, its most likely they will.
this is from 99 f-body LS1 manual:
"In addition to catalyst monitoring, the post heated oxygen sensor has a limited role in controlling fuel delivery. If the post HO2S signal indicates a high or low oxygen content for an extended period of time while in closed loop, the PCM adjusts the fuel delivery slightly in order to compensate."
The rear oxygen sensor, located after the catalyst, is used for fuel trim corrections on OBD-II vehicles.
By virtue of its location, the rear sensor is generally protected from high temperatures and much of the contamination that affects the front oxygen sensors.
In addition, the rear sensor sees exhaust gases that are equilibrated – they have already been converted by the catalyst so that there is very little residual oxygen.
This allows the rear sensor to respond to much smaller changes in exhaust gas oxygen content. In turn, it then possible for the rear sensor voltage to remain near the 0.45 volt switchpoint.
This characteristic allows the rear sensor to be used for fuel control. Under steady rpm and load conditions, the short term fuel trim bias can be adjusted so that the rear sensor voltage is maintained near the 0.45 volt switchpoint.
This ensures that the catalyst is getting a stoichiometric exhaust gas mixture, despite any shift in the front sensor switchpoint.
The rear fuel trim corrections are learned in KAM (Keep Alive Memory).
Internally, this system is known as Fore Aft Oxygen Sensor Control (FAOSC). Note that FAOSC learns and reacts very slowly because the catalyst, with its large/slow oxygen storage and release characteristic, is part of the control loop. Also, this system cannot be used with a "y-pipe" exhaust where a single rear sensor would try to adjust dual front sensors.
Don't let this distract you from the fact that Hector is going to be running three Honda Civics with Spoon engines, and on top of that, he just went to Harry's and he ordered three T66 turbos with NOS... and a Motect system exhaust.
I unplugged rear o2 and went for a drive no cel or pending cell.
Ltft were about half of what they were with it plugged in. It's still anecdotal at this point but I need to go for a longer drive this evening and will watch it.
03-16-2018, 04:42 PM
