hi guys/gals. i have a big(to me) question: are O2 readings supposed to fluctuate erratically in closed loop?

here is the deal: when i start the car cold:
BLM: 128 in cell blk 4
O2 voltage: about 450mv
open loop


after car warms up:
BLM:108 in cell blk 4
O2 voltage: swings from as low as 90mv up to 900mv
closed loop.
this is with the vehicle moving steady speed or at idle in drive or park. after warm-up, the idle is a little high(about 150-200rpms) in park and drive. the only time the BLMs come up after closed loop is when i'm accelerating.


ccp is at 0%
ecm is reading the speed sensor

it is an '87 tpi 350 put into a '91 rs and converted to speed density 7730 ecm
if more info is needed please ask.

 

Yes.
There are voids of lean gases (between the slugs of exhaust gases from cylinders having fired), and the ecm is toggling the injector pulse widths, to AVERAGE an AFR of 14.7:1.

A BLM of 108, would suggest the tune is rich, and the ecm is having to pull fuel out.

 

thank you. that makes sense. now, why is it so rich? the BLMs stay there unless i'm accelerating. is my chip programmed rich or is something wrong somewhere?

 

I find it odd that you would be in FTC 4 even in closed loop, warmed up, and at idle. I am always in FTC 0 at idle. As Grumpy stated, it appears that the ECM is detecting a long term rich condition and is pulling out fuel.

What I have done to get a clearer picture of the BLMs, is simply to drive a specific drive cycle and data log,, and record what BLM value is in as many FTCs that you can put the ECM into.

Also, what are your fuel cell boundaries? It seems that they may be set at values that prevent the ECM from getting into FTC 0.

Also, the condition of the O2 sensor can greatly effect the BLMs. Is it possible to barrow an O2 sensor and see if the BLMs change suddenly?

 

unfortunately it is a mail order chip and i don't have the equipment to change the fuel cell boundaries. i'm using tunerpro to do some scanning and i am getting these readings. i do have a spare bosch o2 sensor i could switch to see if it changes anything.

 

The eprom is way off and not properly tuned. Go ahead and change your O2 sensor, but don't get your hopes up.

Get the equipment and start burning your own. Consider that "mail-order" eprom wasted money and your first lesson in burning your own eprom.