Wondering if there is any way for me to perform any sort of procedure to know when the computer switches from open to closed loop, even if just with something like a voltmeter? Does any other sensor act as the dominant signal for when to switch?

 

Welcome to the forum!

Do you have a factory service manual for these trucks? If not, there is an online one floating around out there that will really help you when working on these trucks. Let us know and if you don't we may be able to steer you in the right direction!

 

Thank you for the welcome!

I have obtained the digital version of the 1992 manual and have been using that thus far. I was reading through the fuel section, and found a table that outlined the stages the computer goes through when receiving inputs durig the warmup and drive cycle. However it's still lacking a bit of info, as it almost makes it seem like it enters closed loop within a minute, which seems extremely early considering the O2 is a simple 2 wire with no heater circuit, and takes time to warm up enough to produce a proper signal.

 

Ultra Gauge will work for that purpose (viewed as voltage which are constantly changing) and also allow you to see couple dozen other areas(PIDS). However, even with a good quality diagnostic scanning tool it is the voltage output reading you would see when connected to the ECU/PCM. So you would need to know the values and what they represent aside from the health of the sensor. As far as I am aware there is no program in any ECU access or otherwise that does simple HO2 or O2 on/off indicators only as the reporting operation.

I know I am going to regret asking but why would you want to know those by themselves? Unless you are checking for proper function, they are not helpful alone, but if you were to be changing ECU perimeters then i could understand wanting to track them.

Your full response is not taking into account the CAT temperature and comparing with ambientes? Also it reads like you do not completely understand the H02 output and what the ECU programing does with that which can vary between platforms and is very different ion the newer Mazda Skyactiv engine.


Ok that is about as much as i am going to say in this thread MeB2000 can take it form here.

 

Ultra gauge would be nice, however that is used for OBD2, this truck is OBD1.

I obviously want to know more than just that, but I wanted to specifically know when it switches from open to closed because I am diagnosing a roughly idle with light misfires. While I was doing some testing, I noticed the truck seemed to start running better once the O2 lit off and started producing a proper voltage for the computer to use. So I'm curious if this rough idle is something pertaining specifically to an issue with open loop state and the lack of an O2 voltage.

There is no CAT in this vehicle, and only one O2 sensor, however I did think about it late that I could use my workplaces thermal images to get a better idea when the exhaust temp has reached the correct temp while monitoring O2 Voltage. I do indeed understand the O2 output and how the computer uses the data for fueling adjustment. (p.s this is a two wire O2 sensor, no heater circuit).

 

Ya oops And u did post 1992. Missed OBDII by 3 years .
And yes the ultra gauge will work. But you need an adapter from OBDI TO OBDII . The Ultra gauge website only list OBDII but it will read most of the PIDs in OBDI.
no CAT no problem. You should use an EGT for the most accurate exhaust temperature readings . And an EGA to what the AFRs then with you voltage information from you O2 you can get an idea when it switch from open to close. But that will only be for that set of deltas during that testing. If ambient temperature changes the results will be different.

You seem to know what u are doing but going the long way around verifying the health specifications of an O2 sensor. Rereading this thread maybe the target points more cold temperature fueling ?

But anything pre OBDII requires more physically looking at things which is why I normally don’t participate on thread like this. Don’t get me wrong I can diagnosis anything which can be described as Old School in the real world .

good luck I will be watching this thread to see how it all gets resolved for you.