Problems in the morning...

Adam, I'd grab the code now. You don't need the CEL to be illuminated at the time you pull codes to retrieve it (the code is stored in the KAM even if the CEL is off). You can also have soft codes (that never illuminated the CEL) stored, so it's where I'd start.

Good luck bud.

Adam, you should see that CEL-triggering code. If the KAM or computer power source loses power for very long, that can cause the code to go away. Otherwise, I've not run into the computer not storing a code (I've had it store codes that never triggered the CEL at all).

You can check the frequency and amplitude of O2 switching with a DMM.

Otherwise, I'm outta ideas - I'm sure one of the other guys on here has some good ideas.

Good luck.

check the simple things first.

Like checking to make sure the harness is on 100%

sometimes it's those little things that screw us


If all the simple things are good, I'd say it's that 02 sensor you put in. Maybe try taking it out and putting it back in shrug: you never know). If that doesn't work, try a KAM reset.

Here's my theory (that may be completely wrong): Your car's adaptive strategy changed things up since you had an 02 sensor that was faulty or on its way out (it adapted to ur old O2's readings). You replaced it with a perfect condition O2 sensor...so that's working like it should, but your computer is still using the values it learned from the malfunctioning one. So maybe your computer learned that "voltage x = stoich"...but now, that same voltage causes the computer to +/- fuel. My guess is it just needs to relearn those values or do a KAM reset.


The only problem with my theory is....that O2s aren't used in open loop...like when you first start your car in the morning. If I'm not mistaken though, your computer uses CL information in its decision making process for OL...so my thoughts may still hold water


rambling I guess, hope I helped some

I am pretty sure the 94-95 EEC-IV reads all sensors even @ WOT.

Regardless, I do know that our cars run rich during cold start-ups and dumps extra fuel to heat up the O2s. Now if you get in your car and drive away without letting it warm up a bit it can make popping backfire noise from igniting the unburnt fuel in the exhaust. Mine does this if I am in a hurry to drive away. If I let it idle for a few minutes no backfiring.

You make a good point about letting it warm up. Our cars do dump extra fuel when starting up. Good call

Now on to the O2s (sry, not trying to hijack your thread Adam)

I always thought that the O2 sensors were only used in CL and that in OL it didn't matter what the O2s were sending. The computers do, however, use stored CL info (like that from O2s), and apply it to open loop starting conditions.

Maybe someone could clarify this...Grady? Anyone