Originally posted by azgn
the Thrasher only idles in open loop...needs 02 from then on...
If you let the BLM's all learn in with an O2 sensor you can then disconnect the O2 and run open loop at all times with the Thrasher. It will then fuel from what was learned. Sames goes with the Extender. MaxEffort on the other hand doesn't need the 02 sensor at all but does help with tuning it.
32. Can I disconnect and remove my O2 sensor? I run leaded race gas and don't want to poison an expensive O2 sensor.
Yes, but only if you have a chip that's programmed to allow you to do this, and to the best of our knowledge, ours are the only ones that do! Conventional chips will set a code and go into a default fueling mode if you disconnect the O2 sensor. We detect that the O2 sensor is not present, and simply continue on in open loop mode and do not set any malf codes. Being the cheap racers we are, we thought it was foolish to keep poisoning expensive O2 sensors when we raced with leaded fuel, so we decided to solve that problem right then and there!
Now, some folks will say they rely on the O2 sensor for tuning purposes. That's good to an extent, but remember the leaded fuel is poisoning the O2 sensor as you're running, causing your readings to become more and more inaccurate and suspect. Heated O2 sensors seem to resist poisoning and last a bit longer, but they'll eventually become inaccurate as well. We simply plug the O2 sensor hole with a plug that has a thermocouple installed, so we can monitor EGTs (exhaust gas temps) and tune with that instead!
Some folks will claim that the O2 sensor is required for proper operation, and their car will run very strangely when it's disconnected. Well, this is what's going on. First, if they're saying their cars run very odd under cruising conditions with either a bad O2 sensor or a disconnected one, they're correct - but only with a conventional chip. A conventional chip will detect a disconnected O2 sensor, set a malf code, and run on some default limp-home fueling which is far from optimal. The Thrasher chip will detect a disconnected O2 sensor, but it will not set any malf code, and will not revert to a default limp-home fueling mode, it'll simply continue on in open-loop mode.
Do not disconnect power to the ECM and clear it's memory before running a Thrasher chip with a disconnected O2 sensor! You can do this, but your engine won't run optimally. Remember the block learn memory (BLM) discussed in question #2? Remember that after driving around a bit, that BLM table has been learned in. Thus, if you don't clear the ECM memory, those BLM values stay where they learned to on your last cruise, and are still in use after you disconnect the O2 sensor. Yes, because you've disconnected the O2 sensor, the ECM will not get out of open loop mode and will not continue to "learn" anymore as you drive; however, the "old" BLM values are still there are being used, and are probably very close to being where they need to be for optimal operation anyway. Thus you at least retain the last learned information from the last time you drove with the O2 sensor connected.
If you DO clear the ECM memory before disconnecting the O2 sensor, then all BLM cells are reset to their normal, nominal value of 128, and no corrections to the fueling will be made. Thus, if there were conditions where the ECM had learned in a significant amount of fueling compensations, this information would be lost, and your fueling will no longer be close to optimal anymore.
Remember too that Thrasher chips reset the BLM at WOT to 128? (See question #10 in this guide for a detailed explantion of why this is a good thing!) Thus at WOT, the Thrasher chip is operating under a true open loop condition anyway, so you'll see no WOT differences in running with or without an O2 sensor connected! Remember, as discussed in question #10, a conventional chip's WOT operation may still be affected by a poisoned O2 sensor because the WOT BLM cell 15 will continue to learn, and whatever random value it's learned to (random because the O2 has been poisoned) is used to alter WOT fueling. A disconnected O2 sensor will affect a conventional chip's WOT operation as well simply due to the fact a malf code will set and a default fueling model will be substituted for the proper chip calibration.
