97 3.4 4wd O2 sensor 2 short from signal feed wire

I am getting 6.4 volts back feeding to the O2 sensor 2. Voltage to the heater in the sensor is battery 12.6. I changed the feed side of the connector and installed a new Denso sensor with 14.6 ohms. Also unplugging the sensor does not trigger cel. Voltage from the sensor is 0.05 ish at idle. But becomes normal most of the time over 2k rpm.
Cat has good temps at 310 an 380.
I got 21 mpg on a 500 mile trip, but am getting 14 or so around town.
Not very good with electric.
The question is, if I can't find a short, is it a bad ECM?
Or should I take it to someone?

 

Check the ground wires at the following locations. Battery negative to inner fender, multiple ground point close the the DIAGNOSE port on the upper intake and the ground at the back of the passenger side cylinder head to the firewall. If there is an insuffieinct ground path back to the battery strange things happen.

The next thing would be to clean all of the crap out from under the passenger side seat. O2 sensor 2 comes up through the floor board there and it sounds like there might be an issue there.

 

Found a ground that went to a computer under the radio. It was rigged, since I've had the truck, 20 yrs. and is again. Reconnecting put the parasitic draw from 10.6 to 12.7 V. Haven't checked at the O2 for back feed yet. But sensor OBD2 Volts is under 0.1 with lower rpm's.
Checked wires by shaking above tranny. No change to V. The wires go to the engine compartment. Shook those too. Pulled fuses again and nothing.
pulled the seats and carpet, the fuel pump wires come through the drivers side floor board. Damage is not visible to any wires that I can see.
The airbag light is now on. All the time. I may disconnect the ground that I put back.
it's an early 97 model made in 6/96 on the door, but toyota parts says 9/96.
I just noticed a computer for abs brakes near the inside fuse panel, but it doesn't have abs.
never been in a crash.
Thanks for the advice.

 

You were correct about the ground, it was causing the airbag light to be on. Also the O2 sensor problem. But it didn't fix the fuel millage. At the same time I changed the knock sensor wire, which was in very bad condition, no light though. Also the intake gasket. So I bought a new HF cheapo Ohm meter and my injectors were bad. 17 ohms. The time I had 21 mpg, with those injectors it was near freezing. I think that is why. I bought aftermarket clones and millage went from 14 to 13. I then got GMB refurbished, tested at 14.9 ohm's, and millage is up to 18, mostly city. The valves are really tight. I attempted to adjust them with the speacialized tools. Only adjusted 2 in couple hours, and gave up. I would not recommend this for a novice. Next time I'll pull the cams. Thank's for the advice.

 

After installing the rebuilt ecm and a few hundred miles later replacing the fuel pump, (denso) the average mpg was 18. Almost no highway miles. The old ecm had a blown cap and I believe it was bleeding voltage to the #2 o2 sensor.
The shop that tried to rebuild the original just refunded the $150 charge. They should not even attempted to fix it. Electronic Fix, Tampa.
Still need to adjust the valves.

 

I dont know what it is, somethings adjusting the valves is a 3 hr job, other times it is 3 days. If any of the valves are out of adjustment a few thou on the loose side I would do this when you have the time, if a few thou too tight, escpecially the exhaust valves I would prioritize this.

Lots of times it is the stiction of the oil under the shim to the bucket that makes it difficult to lift, a little blast of air after a squirt of carb/brake clean at the shim helps.

I have no way of knowing your mechanical experience so please dont take offense to the following... when removing the cam caps mark them as to position/direction and loosen them all gradually and slowly. There will be some valves under tension and can you warp a cam by taking the caps off improperly, possible, but unlikley, but why take the chance. Modern vehicles have hollow cams and they will warp... there is a special jig required that usualy cost thousands.

 

I'll post about the experience after getting around to doing it. Some are pretty tight. I tried the compressed air method and lost track of the first one that came out. Took me half hour to find it. Toyota wanted 2800 plus parts. Thanks for the advice.

 

Hence the 3 hour, 3 day comment.