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Discussion Starter · #1 · (Edited)
Had an 02 pegged, figured wouldnt hurt to replace 260k sensors, especially as the old engine burned oil, they were ashed up some, not bad. Ordered new bosch's from rock auto that were the top sellers. Issue was a bare wire, fixed wire, 02s seemed to be working as good or better than ever. Replaced MAF at same time. After 100-150 miles CEL came on, tbh, i thought it was a trans sensor that lit it, i hit the OD button right as it started to **** into OD and it made it goof for a sec, i assumed it threw a slip code or something so i wasnt in a hurry to check codes between working lots of hours on nights and the weather generally sucking. I was wrong to say the least. 15 codes all related to 02s. At least half are an equal share of all 4 sensors regarding heat circuit, thought i got a picture of the specific message / codes, guess i didnt. 2 or 3 were regarding bank 2 lean. STFT1 -.8% LTFT1 14.8% STFT2 3.1% LTFT2 14.5% These seem to be pretty consistent, at fully warmed up idle (not sure if helpful honestly). There is also short term fuel trims listed for all 4 sensors. Pre cats match the short term above, post cats are both stuck at 99.2%, i have no idea if thats good or bad. The 02s are cycling between .085 and .805v roughly once ever 1.5- 2 seconds, all 4, again, i have no idea what to make of that.

Would like to point out that i never EVER had the CEL come on since owning this thing for the last 55k, and it always ran fine and got appreciable fuel mileage (21-23). Here lately its been getting 18-19, it hasnt been idling much regarding warm ups so it cant be attributed to that. Does seem to have a bit of an inconsistant idle, cackles more on decel than i remember, and sometimes almost seems like a miss if youre partly out of the throttle. Could this be because its a PI engine with a SCP chip? Does the computer just not like these sensors? I cant really get the car back on the lift in the foreseeable future to swap the old 02s back in to rule it out. Hoping you guys can shed some light, I appreciate your time and patience.

 

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Discussion Starter · #4 ·
I was super careful with the sensors, didnt even touch them below the threads, they already had anti sieze on them. So should i focus on putting the originals back in to rule out the new sensors?
 

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Discussion Starter · #6 ·
Why the 02 heater codes as well as never having the issue before hand, but that would just rule out coincidence. I have no idea where to look next. Have checked for exhaust leaks, injectors seem to be working great.
 

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Discussion Starter · #9 ·
Car wasnt "tuned" per say, just has a chip with a canned tune on it. As far as STFT staying near 1, need some context, is -.8 and -3.1 "near" 1? Replaced the MAF because the old one didnt seem to be doing much according to the scantool, .1-.3v iirc, new one does the same thing so i dont think anything is really different there. As far as the sensors cycling, id read that theyre supposed to cycle every 15-20 seconds not every 1-2 seconds, but my take away was that cycling is more or less good. As far as looking elsewhere, care to elaborate? Computer dealy says o2s, i look at o2s, o2s seem to be working... dont have the slightest idea what to do next besides regret doing a tune up.
 

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Discussion Starter · #13 ·
What MAF sensor and injectors was the canned tune written for?

Your O2 voltages seem OK for the most part, though the switching period is a little irregular.

Your LTFTs indicate about 15% additional fueling is required at idle. Either the MAF sensor is not correct in the tune, is acting up (not likely given your troubleshooting), or there is a vacuum leak. It's possible all 4 O2s are junk, but I don't consider that the first thing I'd run to and check. Look at your HEGO fuse under the steering wheel. If that's good do some testing of the harness for shorts on the heater circuits.
Thank you very much for the in depth info. Stock 96 MAFS and 19lb/hr injectors are what the tune was written for. I will find what the IACV is running at. Been all over this thing recently looking for vacuum leaks, i really dont feel like it would be that, but it did recently get much cooler. I will put the old MAFS back in and see what (if) it changes. I didnt "do" anything when i swapped it in, maybe i was supposed to. Only pulled the old one because the car had a K&N on it when i got it and i know that can screw with em, its a little dirty looking, nothing crazy.
 
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