Using a front O2 sensor for the rear O2 sensor slot (briefly)
 

Anyone know if running a front O2 sensor in the rear O2 sensor slot for literally a couple days would cause a CEL?

I know it's largely just emissions, and I know it's not inherently a "problem" from a mechanical perspective. I just have to reinstall my OEM cat for the compression test, and the rear O2 is seized in the BHR midpipe. I have a front O2 sensor that I can put in the OEM cat's rear O2 sensor position, but if it will cause a CEL then it's going to put blinders on the dealer when all I want is a compression test to confirm what I suspect is a failing coolant and/or oil seal.

I also know that there is a price difference in front vs rear O2, which suggest differences in design, so perhaps differences in information read? Even if it's "different", if that difference is still something that the ECU is kosher with, it works for me for now.


Just no clue on this, and don't really have time to "test" it before taking it in.

They are electrically incompatible.
They are entirely different types of sensors and have different connectors.

Bleh. Thanks.

Actually, the connectors ARE identical. But I assume that doesn't change the "different type" bit.

https://www.rx8club.com/attachment.p...1&d=1331332608

Got the rear O2 out of the midpipe. Made another MacGuyver bar. Course, then it took me another 5 minutes to get the sensor out of the socket.

isn't the front wide band and the rear one narrow ? or something like that.

if it were that simple Mazda would have saved the money and done it that way to begin with

Understood, and agreed. I wasn't implying that using a front as the rear was the better option. The front is clearly more complicated than the front. The question was pretty much just a question of "for a few days, will a front O2 sensor return an appropriate signal to the ECU to avoid a CEL." I could easily see a situation where Mazda could have used a wide band O2 for the rear position as well, but decided to use a narrow and much less complicated/expensive O2 sensor for the rear simply because of cost, and in theory swapping the rear is viable, unlike swapping the front.

MM answered that satisfactory, and I went back to getting the rear O2 free from the midpipe. I did get it free and swapped over.

However, on the way to the dealer this morning, popped a CEL for "O2 Bank 1 Sensor 2 heater circuit voltage low" So the heat of the midpipe tune probably fried it anyway, and the AP was masking that. Rendered the whole deal a moot point :)


Unrelated, the dealer confirmed low compression and is submitting the warranty paperwork Monday to see if MNAO will cover it.

:confused::dunno::scratchhe

You are having low compression too? Since when?

Probably for 40,000 miles now.

Cat full clogged at about 55k, and it's never really felt right since. 3 compression tests done within the 4 months after cat replacement resulted in horrible failure that the dealer called passing, just barely passing at another dealer who told me to bring it back in a month or two, and then adequately passing. In that order.

It's still never been quite back to what it used to be and always felt slightly "off". I also started leaving a smoke show at a nearby intersection when starting from cold if I didn't let it warm up completely at idle first. Incredibly predictable. Same elapsed time after starting up cold. New ignition, MM tune vs stock, cat vs midpipe, new O2 sensors... nothing made a difference as far as that smoke was concerned.

I figured the cat failure slightly warped the housing, and I had a very slow coolant/oil leak into the housing that would get shoved out into the header during start, and then would cook off quickly as soon as the exhaust hit the right temp. I always knew there was a bit of oil mixed in, but had always been guessing that it was fuel, possibly a leaky injector. One member shoved his face into the plume of smoke to "analyze" it (something I was never brave enough to do), and said it was loaded with fuel. Considering it looked similar to a very brief seafoaming, I left it chalked up to that.

It's been running "acceptably" pretty much this whole time. Including my SS13 trip that averaged 19.9mpg and had all those tanks over 22 or 23mpg. Even as short as 3 weeks ago, I got 21mpg on a road trip. Still pulled plenty hard.

But, I knew something was changing for the worse. I could feel the idle getting worse, hearing differences in the engine, etc... A bit over 3 weeks ago I replaced the plugs, and one was covered in a goopy substance that 9k said looked like the coolant and oil mix he had on his coolant failure, which was enough for me. Over the past week, I realized that the smoke on startup was getting much worse quite quickly, and was gaining more and more of a blue tint to it, and wouldn't fade as quickly, so I knew it was about done. Just took a bit to get the time to pull the midpipe and reinstall the cat to get it back in to the dealer.

Front: 5.7, 6.3, 5.7
Rear: 6.7, 6.4, 6.7
Unknown cranking speed, but my cold start hasn't really slowed much and on the upgraded starter, so I suspect I'm still around 250rpm.


So, i've probably been under spec in the front rotors for maybe 20,000 miles or so. At about 95,500 on the odometer, so knew I couldn't postpone any longer, and it's fairly good timing since I barely drive it now that I take the train to NY and work from home the rest.


I am probably going to get some flak for letting it go this long, but I'm comfortable with it. If nothing else, who knows how long my reman will last, and if it's only got 30,000 miles of lifespan, I'd rather get it at 95.5k than 71k. :)

I see. hmm 5.7 and 5.7 and 6.3? that seems like an apex failure. or there is a tiny "crack" on the apex seal. either way those numbers means failed.

where u got ur test from ?

I'm going to decline to say for now. I'll wait for the warranty to be approved and everything :)

there is something called "PM" u know :lol:

I don't work for Mazda, u know it. :lol: