High O2 reading, but PCM still sending rich command!

[mena24]

I'm hoping hoping that it's a generic concept for an OBD II vehicle. I know this is not the right forum for this vehicle I'm working on,.. but please bear with me. I needed some info regarding the fuel trim scheme that could shed tlight on this issue. Thanks in advance.

Here it is...

It's OBD II, 96 Plymouth neon 2.0L SOHC

Smog failure for very high CO (9.00%), high HC (amost two times the limit) under load

(15mph and 25mph).

Scan reading says O2 detecting rich exhaust (980 mV) but PCM keeps sending rich command.

LTFT goes up to 24.8 %

All reading goes back to normal at idle.

Here's some of the info @idle RPM using Solus scanner:

Closed loop
ECT = 198 F
MAP = 20
O2 switching fast from around 150mV to 900mV
STFT = 0 +/- 1
LTFT = 0

Here's some of the info @2500 RPM using Solus scanner:

Closed loop
ECT = 201 F
MAP = 22
O2 stays 980mV (O2 detecting very rich mixture) !!!!
STFT = .... (Don't remember, it keeps changing)
LTFT = 24.8 % ( from 0, it keeps going up till it riches 24.8 and stays there)

Is this PCM problem? Why is PCM ignoring a rich O2 reading by sending rich command under load?
What else can PCM look for to calculate fuel other than O2 sensor during close-loop??



Any input will greatly appreciated!!
Thank you!!

[sierrap615]

the PCM watches coolent temp, TPS, MAP or MAF, IAC and O2 as the main inputs for the fuel mixture, and a few other small things like gear, VSS, ect...

check air filter for restriction, plugs/wires for weak spark, spark timing. just my basic thoughts.