1990 LS400 oxygen sensor upstream

[JoeSuff]

90 LS400 64k miles. Service engine (code 25) and Trac light on.

Previously when I bought the car I had a small leak at the rear cat flanges to exhaust pipes. An exhaust only custom shop cut and replaced the bad metal. I was hoping having the offending pipes replaced would fix the service engine since it was right between the two sensors on both sides.  I reset the lights but they came back.

I purchased a set of NTK o2 Sensor (for some reason i thought the were OEM got them confused with the Denso)  When I went to install the sensors I was unable to seat the replacement plug into the engine harness. I pulled them and saw the seperator difference. I can't see into the harness on the engine but it's the only thing that seems to make it so I can't seat the electrical part.  Neither sensor was able to click into the harness but the both screwed in.  I put the original sensor back in with no problem.

I called rock and they said ALL including Denso have the same (+) like style connector and not the (-) like I pulled. I'll buy OEM if I have too But at 3x's the cost I don't wanna spend the money to have to splice harnesses.

Anyone else ever have issue?

[Exhaustgases]

Its been awhile since replacing the O2 sensor for me so I don't remember the plug. So either the tab deal broke off in your other end. Or they are using a different part or mixed things up and that is for a different year. I don't know.

[JoeSuff]

Well i was home for the day.  Thought id try and snap a pic of the engine harness for the o2 sensor, ponder what i could do before dropping $150 for the OE part.   I started with the passenger upstream since that was the easiest to see.  Once i had the harness off i thought id give a go mounting the NTK sensors once again, armed with the knowledge that Rock and no sites i posted to seemed to have any knowledge of problems.  ^^Mr Bob Exhaust Gasses being the only person to offer any personal input.  I'm guessing that the car so old most people have abandoned  following.  

Anyway with a lot of persistent wiggling and the help of a set of long reach bent nose pliers i was able force and finally seat the replacement sensor.  Of course then i had to unclip it, pull out the threaded original and then insert the aftermarket once more.   Im on my 4th restart and 35 miles.  The light hasn't cycled on (yet) .  If i get to 100 miles im hoping ill be okay.  

Incase any other First Gens should follow heres a few pics of the Upstream o2 Sensor connection

[JoeSuff]

Update: All's good, Got to 111 miles on the new sensor and no eng light resurfaced.  I decided to do the Downstream o2's this weekend.  Read a couple threads where best practice would be to to have them all done together.  I'm assuming the holes in my exhaust causes the o2 failure to being with.  I used a set of Denso this time since it looks like everything from underneath the car is a Denso part.  

[sha4000]

Downstream sensors have no effect on gas mileage. They are strictly their as a tell tale for emission purposes.