How to tell if the engine is in closed or open loop?
11-05-2010, 08:58 PM
#1
Burning Brakes
Thread Starter
How to tell if the engine is in closed or open loop?
Installed a new o2 sensor a few weeks ago to try to restore some MPGs. No effect. So i figured it's just because the old one was functioning fine. However, I noticed that there's no difference in idle when I run the car with the o2 sensor plugged in and without, once it's at operating temperature. Is this normal? Just want to make sure I didn't somehow botch the sensor install... I used a universal one, and connected the wires using the little screw things bosch supplies.. although I'm considering just twisting the wires together and taping it since I'm not sure how well the "ez lock" connector things work.
11-05-2010, 11:02 PM
#2
Three Wheelin'
Well, to accurately check an O2 sensor you really need a DSO (digital storage oscillscope) to check the waveform of the O2 sensor signal. If you have a good multimeter like a Fluke with a min/max/average function for the voltmeter, you can at least see if the O2S signal is switching between 0.2 and 0.8V like it should be when warmed up.
The O2 sensor generates its own voltage signal and needs to be hot to work and generate a strong enough signal, that is why our cars have heater circuits so that the sensor heats up faster and is able to send a signal to the DME and start reducing emissions. The DME goes into closed loop based on whether it is getting a strong enough signal from the O2 sensor and it also considers engine (coolant) temp sensor input.
So, I would check and see if the O2 sensor is generating a voltage signal when fully warmed up, or even better, if you have access to a CO meter or wideband O2 sensor, you can see if connecting/disconnecting the sensor makes any difference in the air/fuel ratio (it should be right around 14.7 wth the sensor connected). For what it's worth, on my bone stock '86, it is tuned well and there are no vacuum leaks, etc so it is hard to tell a difference by ear when the sensor is disconnected, but you can see the slight difference when it is hooked up to an exhaust gas analyser (it goes a bit richer).
A quick way to see if the O2S is doing it's job is to create a vacuum leak and see if the idle stabilizes after a few seconds, indicating that the O2S picked up the lean condition and the DME compensated by richening up the mixture.
Bottom line, it is difficult to accurately test an O2 sensor w/out proper equipment, but a decent voltmeter can at least give you a hint.
The O2 sensor generates its own voltage signal and needs to be hot to work and generate a strong enough signal, that is why our cars have heater circuits so that the sensor heats up faster and is able to send a signal to the DME and start reducing emissions. The DME goes into closed loop based on whether it is getting a strong enough signal from the O2 sensor and it also considers engine (coolant) temp sensor input.
So, I would check and see if the O2 sensor is generating a voltage signal when fully warmed up, or even better, if you have access to a CO meter or wideband O2 sensor, you can see if connecting/disconnecting the sensor makes any difference in the air/fuel ratio (it should be right around 14.7 wth the sensor connected). For what it's worth, on my bone stock '86, it is tuned well and there are no vacuum leaks, etc so it is hard to tell a difference by ear when the sensor is disconnected, but you can see the slight difference when it is hooked up to an exhaust gas analyser (it goes a bit richer).
A quick way to see if the O2S is doing it's job is to create a vacuum leak and see if the idle stabilizes after a few seconds, indicating that the O2S picked up the lean condition and the DME compensated by richening up the mixture.
Bottom line, it is difficult to accurately test an O2 sensor w/out proper equipment, but a decent voltmeter can at least give you a hint.
