96 1.6 O2 circuit help

[corolladesparate]

I have a 96 4afe having issues. One item that is causing me some mental anguish in trying to troubleshoot it is the fact the check engine light will not come on for either of the o2 sensors even with them unplugged.

From reading the Haynes manual it looks like it should run in an open loop circuit until it reaches proper operating temperature or 2 minutes +/-. If the O2 does not report back a signal below .7v at 1500 rpm or more the ECU trips a code and runs on the open loop until corrected. I unplugged them one at at time and then at the same time to make sure the ECU was looking or seeing them well after full operating temperature and no check engine light.

My issue is the engine stutters or cuts out at higher RPM, roughly 3100 +/- and feels like it's leaning out. I wanted to make sure the O2 system was OK, but when I couldn't force a check engine light I got confused as to why. I replaced the ECU with a second one and both act the same. Check engine lights on for everything else I unplug like the TPS, MAP, coolant sensor and so on but never with the O2. I have nothing to go buy, but I'm wondering if the lack of a responsive O2 circuit can be causing some or all of my issues when the engine gets to higher RPM ranges, if it is not adjusting the fuel injectors open timing to account for the extra load and fuel need.

My question is where can I find detailed explanations on how the O2 circuit is supposed to work and what tall outside of the O2 sensors are in play. What tells the ECU to close the circuit and start looking at the O2 for input? What can cause the ECU to not look at them anymore? I want to iron this out before getting too far into other areas.I feel like I'm chasing a ghost.

In all I've swapped the ECU, new primary O2, cleaned all grounds I can find, new battery terminals, checked timing belt, different distributor and coil, different ignitor, different EGR it's control valve and actuator, different fuel injectors press regulator and rail, new intake gaskets ( and dug 2-2.5 cups of carbon build up out of the intake passages), new fuel filter and pump, checked the MAP sensor, different air temp sensor, and nothing has made a difference. The car starts and idles good (maybe a bit high, idles at 1100??) and overall still has a lot to offer, I don't want to give up on it yet.

Any help is appreciated!!

[hungt1999]

You might have to drive the car for a while for the Check engine Light to come ON. For some sensors, the ECU requires several engine on/off cycle to perform its diagnostic and report the malfunction

On my car, unplugging the Intake Air temperature sensor by the air filter housing would cause the Check engine light to come ON right away after the first start of the ignition. Try that to see if your ECU reports it.

[speedy25]

How old is your converter? You may not have an electrical fault even though the missing sensor doesnt cause a CEL.

-Pete

[corolladesparate]

To HUNGT1999:

I drove it several miles, still no light, and I've had it running and driven to test the various repairs several time over the last few weeks, and no change. If I unplug pretty much anything else that item throws a code immediately...MAP, TPS, Air Temp, Coolant sending unit, etc.

To Pete "Spedy25":

It's original factory with 225k on it.

Thanks!

[speedy25]

Originally Posted by corolladesparate

It's original factory with 225k on it.

Hmmm you have a stumbling problem at high rpm and you want to blame it on O2 sensors? My guess is you will find a clogged convertor is to blame. I've never seen one last that long unless it blew its guts out by itself.

Summit racing is a cheap place to get replacements.

-Pete

[1jzdreamer]

My 20v has never thrown a cel for o2 when unplugged and neither have my 93/94 4afe's.