Ultra Gauge Users - Open Loop??
#11
08-08-2013, 09:55 PM
The oxygen sensors have a working temperature range, based on expected or anticipated performance of the catalyst. One cannot expect a sensor designed to operate in a 450 degree environment to function normally in a 200 degree setting. For this reason, they come with a pre-heater element, designed to help heat up the sensor and get it into working range quicker on cold start up.
Upon deceleration, all those hot exhaust gasses suddenly vanish, replaced with essentially cold air (air which is taken in to the combustion chamber, and passes quickly through without burning a great deal of gas) and the O2 sensors are cooled.
Before the pre-heater element of the O2 sensor can kick in, the ECU detects the relatively cold condition of the sensor, and switches to an open loop: the modern, computer controlled equivalent of "choke," and automatically delivers a default, rich fuel mixture.
I run a scangauge, and noticed that the system returns to closed loop faster since I changed my pre-cat O2 sensors. But it still goes to open loop upon de-cell. Probably lasts 5 seconds now, whereas it was 15 seconds before new sensors.
Upon deceleration, all those hot exhaust gasses suddenly vanish, replaced with essentially cold air (air which is taken in to the combustion chamber, and passes quickly through without burning a great deal of gas) and the O2 sensors are cooled.
Before the pre-heater element of the O2 sensor can kick in, the ECU detects the relatively cold condition of the sensor, and switches to an open loop: the modern, computer controlled equivalent of "choke," and automatically delivers a default, rich fuel mixture.
I run a scangauge, and noticed that the system returns to closed loop faster since I changed my pre-cat O2 sensors. But it still goes to open loop upon de-cell. Probably lasts 5 seconds now, whereas it was 15 seconds before new sensors.
#12
08-09-2013, 08:54 AM
Super Moderator
These readings are quite normal for these vehicles that are capable of 0-60 in 3.2 gallons.... I mean minutes. But as Nick says, if you were driving on flat ground, steady speed, should not go in/out of open loop very often if ever. And when it drops to open loop it most likely uses a comuter stored defaults, vs the calculated on the fly values form all the sensors.
Last edited by Savannah Buzz; 08-09-2013 at 08:57 AM.
#13
08-09-2013, 09:05 AM
Three Wheeling
Wow, you are pulling **** out of your ***...
Where is all this "cold air" coming from when the throttle body and idle air valve are closed during engine deceleration? That is why its called engine braking. Because the engine turns into a giant vacuum pump and the pumping looses of the cylinders trying to draw vacuum causes deceleration. What fuel is it injecting if MAF is not reading any air movement over it?
You seriously think an 02 sensor cools down fast enough during 5 seconds of engine breaking to trip start up fuel enrichment?
The reason is SIMPLE. Closed loop mode is a circular never ending motion of the ECU firing an injector then reading the 02 sensor, then adjusting the short term trim up or down to maintain stoichiometric a/f ratio.
If the ECU sees TPS as being closed and the RPM over a certain number, usually 1500rpm, it shuts down the injectors. Since its not firing the injectors, it automatically ignores O2 readings (which would be ultra lean for obvious reasons) and that is why it goes out of closed loop.
The reason it goes open loop during Wide Open Throttle is that it switches from O2 sensor readings for fuel economy and emissions to predetermined fuel maps. Hence once again disregarding O2 sensor readings.
Just wanted to add: ECU CANNOT monitor O2 sensor temps, all it can do is monitor the internal resistance of the heating element, as in if it detects too high of a resistance the heater element or wiring most likely broke. The "extra fuel" enrichment you are talking about is to heat up the catalytics as fast as possible to the proper operating temperature before they can....catalyze!
Where is all this "cold air" coming from when the throttle body and idle air valve are closed during engine deceleration? That is why its called engine braking. Because the engine turns into a giant vacuum pump and the pumping looses of the cylinders trying to draw vacuum causes deceleration. What fuel is it injecting if MAF is not reading any air movement over it?
You seriously think an 02 sensor cools down fast enough during 5 seconds of engine breaking to trip start up fuel enrichment?
The reason is SIMPLE. Closed loop mode is a circular never ending motion of the ECU firing an injector then reading the 02 sensor, then adjusting the short term trim up or down to maintain stoichiometric a/f ratio.
If the ECU sees TPS as being closed and the RPM over a certain number, usually 1500rpm, it shuts down the injectors. Since its not firing the injectors, it automatically ignores O2 readings (which would be ultra lean for obvious reasons) and that is why it goes out of closed loop.
The reason it goes open loop during Wide Open Throttle is that it switches from O2 sensor readings for fuel economy and emissions to predetermined fuel maps. Hence once again disregarding O2 sensor readings.
Just wanted to add: ECU CANNOT monitor O2 sensor temps, all it can do is monitor the internal resistance of the heating element, as in if it detects too high of a resistance the heater element or wiring most likely broke. The "extra fuel" enrichment you are talking about is to heat up the catalytics as fast as possible to the proper operating temperature before they can....catalyze!
The oxygen sensors have a working temperature range, based on expected or anticipated performance of the catalyst. One cannot expect a sensor designed to operate in a 450 degree environment to function normally in a 200 degree setting. For this reason, they come with a pre-heater element, designed to help heat up the sensor and get it into working range quicker on cold start up.
Upon deceleration, all those hot exhaust gasses suddenly vanish, replaced with essentially cold air (air which is taken in to the combustion chamber, and passes quickly through without burning a great deal of gas) and the O2 sensors are cooled.
Before the pre-heater element of the O2 sensor can kick in, the ECU detects the relatively cold condition of the sensor, and switches to an open loop: the modern, computer controlled equivalent of "choke," and automatically delivers a default, rich fuel mixture.
I run a scangauge, and noticed that the system returns to closed loop faster since I changed my pre-cat O2 sensors. But it still goes to open loop upon de-cell. Probably lasts 5 seconds now, whereas it was 15 seconds before new sensors.
Upon deceleration, all those hot exhaust gasses suddenly vanish, replaced with essentially cold air (air which is taken in to the combustion chamber, and passes quickly through without burning a great deal of gas) and the O2 sensors are cooled.
Before the pre-heater element of the O2 sensor can kick in, the ECU detects the relatively cold condition of the sensor, and switches to an open loop: the modern, computer controlled equivalent of "choke," and automatically delivers a default, rich fuel mixture.
I run a scangauge, and noticed that the system returns to closed loop faster since I changed my pre-cat O2 sensors. But it still goes to open loop upon de-cell. Probably lasts 5 seconds now, whereas it was 15 seconds before new sensors.
Last edited by Red_Liner740; 08-09-2013 at 09:17 AM.
#15
08-09-2013, 11:28 AM
Super Moderator
Well, I did a test on the way to the tire shop this morning.
Closed loop, 50 mph, foot off gas, and yes it goes to open loop. Does same thing when WOT. Now below 45 mph, I did not see the drop to open loop, and I tried it on flat ground and going up a slight hill (well, what passes for one around here). And at different low speeds. D1 1997, poorly maintained in the past and maintained by a poor boy at the present.
So there may be a VSS signal that is also used in the calculation.
Closed loop, 50 mph, foot off gas, and yes it goes to open loop. Does same thing when WOT. Now below 45 mph, I did not see the drop to open loop, and I tried it on flat ground and going up a slight hill (well, what passes for one around here). And at different low speeds. D1 1997, poorly maintained in the past and maintained by a poor boy at the present.
So there may be a VSS signal that is also used in the calculation.
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