What causes PCM to send rich/lean command in close-loop other than O2 sensor?

[mena24]

If someone can give general info on this, I'll appreciate it.


If you're intrested in a bit more details, here it is...


Here's my problem - PCM sees high O2 voltage (980 mV, but PCM still sending rich

command!

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 I'm desperate and I apologize ,.. but please bear with me. I believe general info would help me get on the right track regarding the fuel trim scheme on this vehicle I'm working on.

Thanks in advance.


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

Now, 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!!

[carnut]

Clogged air filter?

[mena24]

Tried running it with even the air filter housing open, still the same.
Btw, I'm getting 20 in vacuum @ idle, but when I raise the engine to 2500 rpm, the vacuum goes up to 22 in. Isn't that wierd? Or is it normal for a PL Neon?

[silverstangs]

clean the air sensor.. if it's dirty, the wire resistance goes up. the computer thinks there is more air flow that was really is there, thus sending more fuel.