Narrowband O2 signal drop out - Chrome ECU v2

[Dougal]

Hi All,

I'm hoping to get some insight into my o2 sensor signal dropping whenever i have more than idle or cruise load. (when TPS 15%+)
When the car goes into closed loop to target 14.7:1 AFR i can see the 02 signal cycling (between 0.07 volts and 0.8 volts) but as soon as I give any throttle the 02 sensor goes to zero with the occasional blip of a o2 signal (0.5 volts etc...)

As I understand when the car is run outside closed loop parameters it will switch to open loop and use the maps in the rom (fuel map, maf smoothing table VE ?)

I am running a Montero 482 MAF which is scaled in my rom (similar to EVO 399 scaling)
My car is only using 1 x Narrowband o2 sensor. I have set the peripheries in the rom to ignore the front o2 sensor and run just the rear o2.

I have been tuning fuel from the LTFT Low and Mid using the MAF Smoothing table (VE).

My concern is that my fueling way way off and zero in my logs means that its leaning out past the fuel MAP.
My STFT always jumps to +12.5 % addition of fuel whenever i apply load and come out of closed loop and into open loop.
I am unsure if the zeroing out of the NB o2 sensor is reflecting this or its something else related to my MAF or basic tune
My LTFT Low and Mid seem good at near zero (see below attached log)

I'm hoping someone here can shed some light on this.


Attached is an extract of one of my datalogs showing the o2 signal dropping out and a extract from evoscan showing the o2 cycling when idling.

o2 sensor drop out.jpg
o2 sensor cycling.jpg

Also attached is one of the notes in Evoscan regarding o2 sensor signals for high loads that are below 0.7 volts.
How could i test that this is actually an issue caused by MAF iteslf?

EVOSCAN Note for 02 sensor.jpg

The Montero 482 MAF scaling, size and adder im using.
482 MAF scaling size and adder.jpg

Is this just a matter of adding more fuel via the MAF smoothing table (VE) at the load area's (above 100hz) that is there the o2 is showing zero volts?

[striker2]

30% TPS is not enough to go to open loop unless you are above 4000RPMs (there is a table in ECUFlash that shows the RPM vs TPS required for open loop), instead it is switching to the mid fuel trims at that point. Your fuel trim is maxing out is because your O2 sensor is dropping and the PCM thinks its wicked lean and needs to add a bunch of fuel. You could have a bad O2 sensor, bad wiring for the O2 sensor, or even an exhaust leak after the turbine but before the O2 sensor (can pull air into the exhaust system which causes a lean reading on the O2 sensor).

[DrGonzo]

I have been battling this same issue, on two different cars using Chrome and have still not figured out why the 02's just drop out randomly. I replaced all sensors, checked for leaks, redid all wiring, etc and the issue still occurs. Happens on my 93 Stealth and a friends 96 3000gt. So don't feel like you're the only one it is happening to.

I get the same responses about it's the sensor, the wiring or a leak and none of those have resolved the issues with it dropping out randomly. I have my idle dialed in as best as I can but as soon as an 02 drops out it messes up the trims all over again. I'm pretty sure it is my rear that always drops out. May be the front. It is always one bank that does it.

[striker2]

are either of you using actual 98/99 ECUs or are you both using clones (from whoever)?

[DrGonzo]

Got mine directly from Jester. So whatever it is that he sells.

[RealMcCoy]

Is your O2 sensor heater working?

[Dougal]

are either of you using actual 98/99 ECUs or are you both using clones (from whoever)?

Jesters chrome ecu for GTO 91-97 is what i bought.

[Dougal]

Is your O2 sensor heater working?

Yes

When installing the o2 sensor I tested the wiring to the o2 sensor.
I am using a Bosch replacement and wired in as per instructions from Jeff.L on Steath316 site.
http://www.stealth316.com/2-oxygensensor.htm

[RealMcCoy]

Well my first thought was it was really going that lean, but according to your wideband it's going pig rich... If that's correct, it would indicate the narrowband is lying...

[Dougal]

30% TPS is not enough to go to open loop unless you are above 4000RPMs (there is a table in ECUFlash that shows the RPM vs TPS required for open loop), instead it is switching to the mid fuel trims at that point. Your fuel trim is maxing out is because your O2 sensor is dropping and the PCM thinks its wicked lean and needs to add a bunch of fuel. You could have a bad O2 sensor, bad wiring for the O2 sensor, or even an exhaust leak after the turbine but before the O2 sensor (can pull air into the exhaust system which causes a lean reading on the O2 sensor).

Valid points.

Swapped 02 sensors as I have an extra Bosch sensor I bought for another car.

Wiring conditions are fine however it wont hurt to test resistance along the wiring to see if that affects things.

No exhaust leaks very certain of this.

I will do some looking at the wiring again