Looking for input.
1989 pickup, 3VZE. I had a CEL for months, code 11 (momentary power loss to ECU). I finally dug into it. I couldn't find any problem with ECU power. I started through the procedure to check out the ECU, I found the test for VS to E2 not indicating correctly. The value was not changing with engine rpm. I pulled the connector to the AFM, ohmed out some pins, plugged it back in, and when started again the CEL was gone. I re-seated the connector a number of times because it seemed the AFM was okay, but there was a problem with the connection. I'm pretty sure I fixed that, but now I'm getting a CEL, with a code 21. I checked the resistance through the O2 sensor, it's on the high end, but it's within spec. I checked the signal for the O2 sensor at the test point, when I put my Simpson analog meter on it at idle, there is very little voltage. When I rev up the engine, after about 30 seconds, the needle starts fluctuating about once per second, indicating that O2 sensor output is okay. CEL stays off at idle, once it came on while revving the engine, usually it comes on when I start test driving, the first time I accelerate.
Given that the original problem seemed to be at the AFM, and the ECU indicated a power problem, I'm questioning the integrity of my ECU.
I have not checked voltage at the O2 sensor heater yet, I just saw where code 21 is on the heater side of the sensor. Is that correct on OBD1?
Would the O2 sensor heat circuit even be operating when the engine is up to temperature?
Does it make sense that I would get a code 21 when I accelerate the first time on a test drive?
I thought that the O2 sensor may be dirty (carbon, soot) from running rich, due to being in open loop mode from the 11 code. I thought maybe driving it after the fix might burn off the crap, but it doesn't seem to.
I was going to pull the O2 sensor and try to clean it or replace it before I saw that the fault indicates the heater side. I'm shying away from that now.
I'm thinking of checking for voltage to the O2 sensor heater, and checking input at the ECU first, then maybe going through the ECU test again. Also thinking about opening up the ECU and doing a visual inspection.
Anyone else seen codes that didn't point to the problem?
Anyone got any similar experience they would like to pass on?

 

Okay. Last night I was trying to test the O2 sensor circuit some more. I don't see battery voltage for the heater side of the O2 sensor connector.at the plug near the sensor. If I understand the wiring diagram correctly, the white / red wire should have battery voltage any time the key is on, and that wire is coming from the test connection box where you put the jumper on to check for codes. I'm struggling with the wiring diagram. Can anyone confirm?