Caution: O2 Sensor

[Cyberblue]

First of all, I write this as a precaution so that people like me, newbie - yet kinda jackass, would learn from my mistake. This might sound dumb, but I believe I'm not "one of a kind" here on earth. Here's the story:
I was thinking of putting hi-flow cat on my 6th gen, but accidentally purchased a wrong hi-flow cat type (I got 92-95 instead of 96-00). The one that I got doesn't have a hole to plug in an O2 sensor, while actually I need that stupid hole. Thus, I couldn't put the original O2 sensor and unplugged it. Then the "engine check" light came on, somehow it sort of disturb me. Trying to get rid of it, I plugged back the connector with the 4 O2 sensor wires cut, to hook some of them hoping to "emulate" an O2 sensor that was supposed to be there. After few trial and error the light still came on. I gave up, and unplugged it again, drove around for a few miles. During that time, I noticed that the speedometer was dead, the rpm (is it tachometer?) was bouncing up and down. I parked the car and after a few minutes when I tried to start it up, the battery was drained out. Bottom line, I didn't realize that by doing that experiment I had broken the alternator. It cost me almost 400 wing-wangs! I thought the wires from the O2 sensor went through a fuse before it got in to the system, but I was totally wrong. I know I should've seen the wiring diagram before trying to do that.
Morale of this story: don't do anything unless you have enough knowledge or at least a reliable reference such as CL seniors' opinion or corresponding tech data sheet.

[Toyz-B-Us]

The ignition source on the o2 is fused, but if you wired the ignition part of it to another wire to the ecu, there would have been enough resistance to have high enough current to blow the fuse.

[imported_camelian]

hmm, i just put a hi-flo in my 6th gen and just taped up the O2 sensor. i'm running on an OBD1 ECU though so i didn't get a CEL

[imported_DIYperformance]

This is long but you'll learn a few things:

First with what toyz-b-us said, it sounds like you did blow a fuse, and I would guess by the way it was written it is because you cut the o2 wires and plugged it in hoping to trick the computer into thinking it doesn't need one- or at least that's how I understood it. Here's my thoughts:

Did you get your alternator tested before replacing it? Because from what you wrote it would sound as if you only blew the alternator fuse causeing the alternator to not be able to release it's charge to the battery causeing the battery to drain. But the alternator can hold that charge all day. It won't hurt it, but as long as that fuse is dead then so is your car. My question is what did you do about it? Did you have it towed to a shop and that's what they told you? Cause I would bet the alternator was fine.

Second thing: You obviously sound a little new at this stuff so let me help you with something important that you might not know. Whenever doing ANYTHING electrical, hell even mechanical in my opinion, unhook the ground wire to the battery. Just in case you didn't know, that's all. Because you'll blow fuses left and right while it's plugged in, which I guarentee is what happened. Your speedometer died because the VSS (or vehicle speed sensor) is connected with the alternator. BUT, if the VSS dies the alternator will still be okay, just not the other way around.

Now for your o2 sensor issues: you can't unhook the sensor and be done with it. You're using an OBD-2 ECU (your cars' computer) so it must see 2 sensors. Here's your options:

1. Get the right high flow cat. Seriously, go to ebay right now- $40.
2. Keep what you have and lose the second o2 sensor, and hook up an o2 simulator. Again, ebay - $20. This piece will trick the ECU into thinking you have the second sensor still hooked up. You don't really need it anyways, it doesn't monitor your A/F ratio like the first (primary) one does.
3. If you plan on doing heavy mods and tuning, you could do what camelian did and get an OBD-1 ecu (which will require more than just changing computers though). It wouldn't require an 2nd o2 sensor because the older emmissions didn't require it.

PM me if you need anymore help.

Originally posted by camelian@Apr 7 2004, 08:51 PM
hmm, i just put a hi-flo in my 6th gen and just taped up the O2 sensor. i'm running on an OBD1 ECU though so i didn't get a CEL

ODBII uses 2 02 sensors, ODBI only uses one