AFR stuck at 14.85 - HELP
 

Hello everyone,

The AFR on my accessport V3 is stuck at 14.85. I noticed the problem when it would intermittently peg at 14.85 but then work normally. I know the car isn't actually running lean and in fact is running rich for many reasons; the exhaust smells like fuel, the spark plugs are carbon fouled, my fuel consumption is really high and my LTFT are pegged at 20. This is because the 14.85 AFR is being read and trying to be corrected.

Im getting the codes:
P2187 - lean at idle
P2177 - lean at off idle
and the code for o2 sensor low voltage which I forgot the code for

I've replaced the o2 sensor already and need more ideas on what to look for. Is it possible I bought a dud o2? Is the problem with my harness?

There are two O2 sensors. If your AFR is pegged at 14.85, then it is probably your primary O2 sensor that has failed. If you only replaced the secondary, then that wouldn't have addressed the issue with the primary sensor.

Also, did you buy a new O2 sensor, or was it used? If it was the latter, there's every chance that the sensor was already fouled by the time you got it.

I replaced only the primary, not the secondary. It was a brand new $170 sensor

Have you captured logs of and/or monitored O2 voltage? I think it should be like a waveform going up and down on the primary if i recall...

If your AFR is static I would assume the signal would be as well coming from the O2 sensor.

Also, what intake are you running?

I had crazy high LTFTs (15-20) w/ the MSCAI, adding the air straightener brought it down to 5 in less than 5 min idling. My exhaust wreaked of gas too, super rich.

I have not captured logs of or monitored o2 voltage. Can I do that through my AP?
And I think my LTFTs are so high because for some reason my ecu is reading an AFR of 14.85. If the problem was with the AP for example, the car would run normally because the o2 sensor is actually working, but the AP is not.

The AP is not the problem, though your tune could be an issue.

Could you please post a full list of your modifications? That may help us assist you in diagnosing your issues. In fact, if you could put your full mod list in your signature, that would streamline future diagnoses.

yeah lol that would help

OK, and if I recall correctly, you're running a Cobb OTS stage 3 93 tune.

That tune is, at least theoretically, reasonably appropriate for the modifications on your car. So...

That brings us back to electrical issues (i.e. sensor/wiring harness/harness connections/etc.).

You might want to check out this thread: http://www.mazdaspeedforum.org/forum/foru...4-85-a-193982/

There are a couple of possible solutions in there, ranging from replacing a bad fuse or changing spark plugs, to having to replace the ECU.

As a place to start, you might want to try checking the ENGINE BAR fuse.

Where do we get our AFR data, is that not from the 02 sensor?

I took a look at that thread before starting this one. I've replaced all my spark plugs gapped at 0.28 and checked all my fuses with a multimeter including the engine bar 3 fuse which I hoped would be blown because thats an easy fix.

Is there a thread that explains how to test if the female connectors on the wiring harness are good or bad? I'm guessing testing for continuity or something?

I'd imagine this is possible, although I haven't got to play w/ my accessport yet. My simple OBD2 Bluetooth adapter had this ability so I would be shocked if the AP did not. I'd definitely want to start there to be sure you're getting valid readings from the O2 sensor.

Is it possible the person at autozone sold me the wrong o2 sensor?
Could someone tell me what the part number is for the primary o2 sensor for a gen 1 ms3?

you might want to return that, drop more coin and get an oem sensor.

cant return it because I've installed it already and drove with it on. So that was $200 that could've gone towards a tune.
Anyone know which one I should get from rock auto? They have many options.

I feel like you might be jumping the gun here, have you made any efforts to see if there is valid sensor output yet? Beyond the AP or a BT adapter you can probably back-probe a connector.

So correct me if I'm wrong but isn't there a bunch of threads stating to stay away from aftermarket O2 sensors? Maybe it's just me and I'm full of shit but keep wasting time and money on a different aftermarket ones or just buy an oem one and be done if that is indeed your problem. I get it they are expensive and it'd be nice to put that money on towards a tune.

I actually want an OEM sensor, not after market. When I went to the store, I asked for OEM and they gave me an NTK. So my question is, how do I go about getting an OEM sensor? I heard denso is the OEM one but Im not sure.

I might be jumping the gun, but I have no idea how to back-probe the connector to check for valid sensor output.

NGK/NTK and Denso are fine.

so this means either I bought a dud or the problem is with the harness or ECU (?)

Could you post a couple of datalogs including some at idle, and at least one WOT log from ~3000rpm to at ~6000rpm?

To setup your parameters to log (be sure to select o2 sensor options):
https://cobbtuning.atlassian.net/wik...talog+Monitors

And to log:
https://cobbtuning.atlassian.net/wik...How+To+Datalog

Gen 1 OEM primary O2 sensor:

https://edgeautosport.com/mazda-oem-...d-6-2006-2007/

Be sure you get the Gen 1, as Gen 2 is different.

Have you done any major work to the car recently? I see you have a built engine.

Maybe check for corrosion or damaged wires in the o2 sensor and ECU plugs.

I took it to the shop to have a K04 turbo installed because the GTX3071R that was on previously failed.

Is there a diagram that shows what each pin in the ECU plug is for? That would help alot.

I could post a log at idle after work, I dont know how comfortable I feel doing a WOT pull because when I do, the car hesitates almost as if I stepped off the throttle and then stumbles alot almost like rapid fire boost/fuel cut. I'll try and log that so you guys see what I'm talking about

There are a couple of wiring diagrams (including pinouts for various components) for the MS3 and MS6 in the VIP section. I think there's only one for the GenPu MS3 though most things should still be the same in the engine compartment.

If you're getting strange behavior at WOT, then if you can capture a log that shows what's going on, that will help a lot.

Please make sure that you're datalogging at least the following parameters:

Accel. Pedal Pos.
Actual AFR
Boost
Boosted Air Temp
Calculated Load
Coolant Temp
Engine Speed (RPM)
HPFP Actual Pressure
Injector Duty Cycle
Intake Temp
Intake Valve Adv.
Knock Retard
Long Term FT (LTFT)
MAF Voltage
Mass Airflow
Short Term Fuel Trims (STFT)
Spark Advance
Throttle Position
Vehicle Speed
Wastegate Duty Cycle

Sorry, I may be wrong but I thought cobb ots did not have a tune for a catless dp.

No, not a catless downpipe.

They don't as I'm pretty sure OTS maps are made for COBB products, and COBB only sell catted DPs.

Here are some datalogs; a cold start log, and idle log after it's warmed up, a third gear pull from 3k to 5k and a fourth gear pull from 3k to 5k respectively

Yep...that definitely looks like a bad O2 sensor reading to me. Are you sure the connectors are fully engaged for the O2 sensor pigtails? Are the pins in the connectors in good shape?

Okay, so I checked all the connections, all fully engaged. No melting of any wires from what I could see.

Got a new code though, P0140 - Bank 1 sensor 2; no activity
No other new codes.

Sounds like you should probably check/replace your secondary O2 sensor!

Also, you might want to read this thread: http://www.mazdaspeedforum.org/forum/foru...9-p0140-46971/

It's possible that you have some debris in your exhaust system.

I was just reading this thread what a coincidence! And by debris do you mean metal flakes from a blown turbo? Because I definitely blew my turbo, and metal flakes definitely went everywhere.

Yeah, metal debris from your turbo could've fouled the sensor, just as excessive oil, fuel, or even chunks of catalyst (though you're cat-less, if memory serves) could damage the sensor.

So from what I read on the other thread is that the rear is used to calibrate the front. But does that mean if the rear doesn't work the front sensor will not work at all? If so, why am I just now getting the code for sensor 2? weird.
My turbo blew a long time ago. Disassembled all piping and there wasn't much metal in the piping or intercooler, nor in the oil pan magnet.

I'm not sure about that, but it may have to do with the number of drive cycles that the ECU needs to go through after each ECU flash before it can determine that there is a fault with the secondary O2 sensor.

Sorry if i missed this info above, but: what happened to your original OEM O2 sensor?

Was that a casualty of the blown turbo? Or oil leakage leading up to the blown turbo?

I couldn't tell you. Possibly. When the turbo blew, the O2 sensor still worked for a few weeks. After that, the sensor worked intermittently where it would peg at 14.85 but work normally sporadically.

This leads me to believe you may have a fault in the connectors/wiring for the 02 sensor. I know some people have had issues with the aftermarket O2's, but is it usually a dead reading like you are seeing with static AFR? Probably need to figure out what pins the O2 sensor(s) use on the ECM connectors and test the wiring from the ECM to the O2 connector. If there is a fault there and wiggle tests don't show the issue you may need systematically trace that circuit between the two until you find the fault (assuming you find one on the first place).

Possibly a wiring harness rubbed through on an engine component. I might start looking near hose clamps next to the ECM harnesses as this seems like a common failure point.

I found an ECU pinout on the forum. I'll take a look after work to devise a way to check the harness. Possibly using a volt meter to check continuity (?). Only thing is that more than one pin is used for the front O2 sensor but I should have a better understanding once I have it in front of me.