The '95 only has a precat sensor screwed into the front of the cat right between the 2 pipes going in.

 

Good catch! I lost that detail in the noise.

 

Alrighty then I will give this a try on my next day off, so you wont hear from me till next saturday. Just one question, why doesn't it throw a code for this?

 

It eventually will, if you feel like driving it that way long enough to see it for yourself. I don't recommend it, though. It's not at all good for the engine.

The glitch comes by way of the fact that the PCM does not have any reliable reference against which to compare the operation of the sensor. There is a very broad normal, perfectly normal, range of operation for that sensor, and during this end of life failure mode the output signal falls within that range. It's a grossly inaccurate signal, but it's within the expected range of normal. Let it go long enough and the output signal will eventually fail to fall within that range, and a DTC will be set for it.

 

Thankyou. that explains it quite well.

 

You're welcome. Please do report back after swapping that critter out. Oh, and don't forget to disconnect the battery negative cable before starting work.

 

Not trying to thread jack but being we are on the topic; let say the rear (bosh) 02 sensor is "working" as far as the ECM is concerned.. with "Ready or OK" Status (emissions testing) but not actually reading. I say this because when my cat blew out after getting bad gas one time.. i never poped a code; and I drove around with a blew out cat for a few weeks.. smelling up anyone near.. LOL so i presume it's not actually reading and reporting back any real numbers to the Computer as it should have tripped a CEL.

Would it be safe to assume the Upstream O2 might be doing the same thing? Not really reading anything but just giving OK status. The upstream is factory.

 

If the engine is running normally, the sensor is okay.

 

Okay pulled the O2 out it is broken so that is definitly a problem new one will be in tonight will let you know how it acts.

The new sesor is in and all is well with big red, now have to fine reason for loss of vacum under acceleration.

 

This is manifested as your vents switching from dash or floor to defrost? If so, it's likely a check valve. Somewhere around here there's a thread about "wild vents" that'll get you going in the right direction. Good luck finding the thread with the lame search feature that comes with the forum software.