no more codes on '95 GM ecm...still running rich.

[Peter Fenske]

Hi David

Sounds like learn is not being enabled.
Learn is usually enabled at a higher temp than closed loop
The O2 sensor must also move a bit from the 450 mV set point
There is also as posted a setpoint for learn with tps.
Check and make sure the thingy is running at the correct learn
temp.

gl:peter

Ps most scan tools will report learn enabled.






David Curtis <spdrcr at flash.net> on 11/30/98 10:16:17 AM

Please respond to diy_efi at efi332.eng.ohio-state.edu
                                                              
                                                              
                                                              
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 Subject: no more codes on '95 GM ecm...still running rich.   
                                                              








Finally got my ecm scanned, and found only one code..43...knock sensor.
The knock sensor was bad..replaced it, no more codes.

 Now then, we get into ecm operational area.

  This is a '95 Z28 ecm on a LT1 in a '67 Camaro.

 At idle, the left and right O2 sensors are reading 935mV and 940mV,
respectively.   This is in closed loop, as confirmed by a TECH II at my
local dealer the other day.
  The O2 readings may vary to 860mV to 960mV when I rev the motor, and
when I drive around town.
  We did hook the car up to an emission sniffer and confirmed rich
conditions.
  Besides the O2s reading almost constantly high, we have another
strange (to me) situation.  Both long and short term fuel trims are
staying right at 128.  While idling and driving, the scan tool shows
absolutely *no* adjustment of the fuel trims.
  Isn't this "impossible?"   Even if the O2 readings are false to the
high side, shouldn't the fuel trim show adjustment?

  We checked to make sure the O2 circuits were ok...they are.
Nevertheless, we swapped in new O2 sensors..same results.
 We also swapped in another ecm with same '95 Z28 calibration.  Same
results.

 Again, no codes being set.  TPS, IAC, MAP, MAF, etc...all showing
correct readings.

  Any help for this "newbie" to the ecm world would be much appreciated.
Where should I look for this problem?
 Thanks,
David Curtis
mailto:spdrcr at flash.net