Threw a refurbished AFM from Fuel Injection Corp (on Partsgeek) in the 4Runner last night. I bench tested it and it passed without issue. My old one was fine, but we're in "throw parts like a dart" mode right now. No change at all, negative or positive (cold start, then warmed-up closed loop).

I still was never comfortable about the O2 testing, since I only tapped into the Ox single wire diagnostic port to get the < 1 volt based readings. I found some great older articles on Vf testing, and decided I wanted to get access to the Vf signal to match the FSM tests (0V - 5V scale) as those documents give indications on what is lean vs rich in terms of the Vf static reading, and may indicate what could be wrong. Note my sensor has never thrown a code.

First, I unplugged the o2 sensor and ran it. I should have done this first as it runs great (just like on cold starts as it forces it into open loop). But as always, run it for awhile with a change you think solves the problem, and after about 15 minutes of driving, it's back to it's old put put's out the tailpipe. I was reading somewhere that even though it's technically in closed loop with the o2 unplugged, eventually there will be some tweaks to the base mapping after an extended period of time, thus re-uncovering the original issue. At first I thought "awesome, it's my o2 sensor or my wiring" but then I was crushed.

I found the Vf wire in the larger, 3 wire diagnostic connector on the driver's side fender. I knew it was there but had no idea which wire was which. This is for early 22RE's and the only documentation I could find with pictures was for later ones with the diagnostics in the fuse box. 1985 FSM doesn't even have the large o2 sensor diagnostics plug in the wiring diagrams. I found a 1986 wiring diagram pdf somewhere and it showed the o2 connector and the color/name of the wires. It has Vf (grey), E1 (brown) and B+ (black).

1986 22RE EFI Wiring Diagram - with o2 Diag Connectors

So I found this awesome Altavista-era website that had some great details on voltages for o2 sensor testing:

Toyota Vf1 - o2 Sensor Detailed Testing

I ran the truck for about 15 minutes to get it solid in closed loop, and to make sure after the o2 sensor unplugging it was relearning and storing a new value. With the DVOM, and the TE1-E1 diag connector jumped, I was able to see it fluctuate between 0 and 5 volts. Normal. Then I disconnected the TE1-E1 jumper to get the stored correction value: 3.52.

If I look at the scale here on the site I referenced, 2.50V is considered perfect with no corrections needed by the ECU to adjust fuel up or down. What surprised me, is that at 3.52V, it's actually on the lean side (prior to correction). However, the guide says it's still within normal. All the while I thought one of the issues could be a leaky injector, and that's now been ruled out. But the culprit now lies in air issues: vacuum leak, exhaust leak, etc. I don't think it's an actual o2 sensor issue, though I may try and fish out my old 1 wire o2 sensor and see what happens there.

I don't really think this told me much, since it's in the realm of normal. And I've definitely done my vacuum leak checks. My exhaust could be something to look at, as I do use the clamps that came with the LCE header and pipe and I saw some soot around one of the clamps pre-o2 but it's as tight as I can get it. I have to take it next week to get a hanger re-welded, so I'll see if they can do a test for leaks while it's there. I should just get it all welded up and be done with it, especially that small pipe with the o2 and it's connectors.

Still to try:
- New fuel pump
- New distributor
- 1-wire o2 sensor

Thoughts?.. Prayers (at this point) ?