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

[Bruce Plecan]

-----Original Message-----
From: Roger Heflin <rah at horizon.hit.net>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Monday, November 30, 1998 1:27 PM
Subject: Re: no more codes on '95 GM ecm...still running rich.


This sounds like what ScottS was talking about the other day.  I'd say hook
the scan tool up, and go sensor by sensor, looking for something being
wrong,
ie one by one unplug them and see what the scanner reads..
When done with the sensors I'd look, for a wiring error.

Bruce
>
>
>>From all of your info,
>
>The only thing I can come up with is that the WOT (open loop) percent
>throttle values where changed to maybe 0.   On my 93 Z when it goes
>open loop from too much throttle the only thing different is that if
>the block learns are below 128 the go to 128, if above 128 they stay
>there.  But if someone had adjusted the WOT percent throttles to be 0%
>then the car would never learn, and always be at 128.  This is just a
>wild guess.  You might get details from the person that programmed
>your ECM of what they did (assuming you got an aftermarket
>adjustment).  I know some of the aftermarket companies change the WOT
>% throttles  cutover points.  This is the only adjustment I can see
>that would exhibit this behavior.  Anything else should leave it in
>closed loop and adjusting the BLM and integrators.
>
> Good Luck
> Roger
> 93 Z28
>
>On Mon, 30 Nov 1998, David Curtis wrote:
>
>> 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
>>
>