Oxygen sensor problems

Not really fun, but here is what it does. 87 Renix 4.0 auto

It will not read changes in oxygen levels. This is now the second one I have installed, both new Bosch sensors. The first one read O2 for about 10 minutes at various rpms, then stopped and only shows .33v on my Snap On scanner. It would read at higher rpms, for a short time, then down to the same .33v. The second one worked for about 2 minutes and then reads the same. Seemed once the sensor had gotten hot, it quit, but still measures good on the ohmmeter. On the cable, it has 12v, ground,5v like it should.

So now my question. It seems the computer will revert to open loop at drastically increase the pulse width without the O2 sensor working, but when it tries to return to closed loop, which it does repeatedly, it starts to cut back the pulse width without a change in the oxygen sensor level. Now is the sensor fouled or is there a problem with the sensing circuit in the computer?
The only other change is intalling a header. Would that do it if it had a big enough air leak?

Thanks.

I had a simliar problem, the O2 heater wire was working intermittenly (I believe the orange wire), and it gave a low voltage reading when the heater wasn't working. For me, it was just a loose connection at the O2 heater relay. If that is not it, than check for resistance on the signal wire going to the ecu, it should be pin D9. Hope it helps

I thought about the heater relay and even ran a bypass wire straight to the battery as a test with no change.

Time to test the rest of the harness then.

The strange part is the sensor seemed to work when the engine was relatively cold, but once hot, it would not work. After allowing it to cool, it is still bad, like one cycle burned it out. Then installed the second one and got the same result.

The first sensor I took out did have some black soot on it but not enough to foul it or block the holes. I know it is running way rich with the oxygen sensor inop.

Ok, I started it again and with the engine cold, it showed .54v, then slowly dropped back to .33v as it got hot. I then removed the O2 sensor and it has the same light black soot as the first one. With the SnapOn scanner hooked up, O2 voltage to the computer shows .33v hooked up and 4.98v unplugged. This tells me the signal is getting to the computer but the sensor is not changing the value, regardless of actual O2 content.
The O2 heater works. The ceramic was friggin hot. Way hotter than the header. Is the O2 sensor bad or is there something I am missing?

Can your SnapOn scanner read KAM (keep alive memory) to see if there are any sensor faults?
Are you using a stock sensor, or change to something else with the header change?

I've read it's supposed to change output at approx 2 sec. intervals when warm.
What happend to make you change from the used one?
If this all occured with the header, maybe you are thinking right about that...
I should check into mine ('88). It's been unhooked since I bought the XJ,
Best mpg - 20.

Ten High said:

bear in mind that the renix o2 is a different animal than the ho sensor. i don't recall the specifics, check 5-90's site maybe. my '87 had an aftermarket bosch sensor in it when i bought it and it never ran right, always too rich. after reading up on it here, i bought a dealer o2 and it's been fine ever since. just food for thought.

Click to expand...

Interesting thought, but think I found the problem. After installing the third O2 sensor, also Bosch, I noticed something. While reading the scanner, it would stay low, just like the previous sensors, but then I revved it a few times. During the Decel mode, where the injectors are cut off, the oxygen readings came back into spec. The only time they would come into spec was during the decel mode. Seems the "rebuilt" injectors I got are crap and leaking. I pulled the plugs and 5 of the 6 are black and wet. So time for some NEW Ford Motorsport #24lb injectors.

Yes, the Renix oxygen sensor is different in that it uses a titania(sp?) sensor that acts as a variable resistor in response to changes in oxygen levels. The later oxygen sensors create voltage dependant on oxygen level.

Thanks for the ideas.