Re: Tuning Eproms (was ECM 1228746 Help)

[Shannen Durphey <shannen@grolen.com>]

WEG1192@aol.com wrote:
> 
> In a message dated 08/14/2000 3:19:55 AM Eastern Daylight Time,
> WEG1192@aol.com writes:
> 
> <<  found this ECM #1228746 in Ludis's site and it is listed as using the
> same circuit
>  board as the 1227747 ECM. I also found a bin file for it in the DIY incoming
>  ftp. But I can't find the pinout diagram. Does it use the same pinout as the
>  7747 if it has the same circuit board? >>
> 
> Anyone?
> 
> Also, disconnected my O2 the other day and drove around to see how "off" my
> EPROM was. The voltage on the disconnected O2 was never below 0.7 volts and
> sometimes up to 0.9 volts. And this was without resetting the BLMs back to
> 128. I bet if I take power from the ECM and do this again, it may not run at
> all. Any comments?
Yup.  You're reading is not accurate.  The ecm has a bias voltage that
the o2 sensor must overcome. This is to help insure that the sensor is
warmed up and providing a good signal before entering closed loop. 
Measure the key on engine off voltage at the ecm side of the O2 sensor
connector, with the sensor disconnected, to find the bias voltage.  If
you don't account for this, all your O2 voltages will be high.
> 
> Also, concerning tuning EPROMS. I can see why you would want to tune the fuel
> to get the BLMs to 128. You are basically getting the mixture right on to
> where the O2 is a redundant sensor. But the timing seems to be a different
> situation. Since there is no timing equivalent of the BLM (other than the
> knock retard safety device), is it possible that GM sets the timing where it
> is to minimize emissions such as NOx at part throttle? Maybe do-it-yourself
> tuners should concentrate on timing at WOT only since its a free for all
> there, i,e, emissions be damned. 
Yeah, do that. WOT only.  Don't worry about over rich deceleration,
stalling, incorrect idle speed, lost mileage during part throttle
cruise due to detonation, poor cold weather driveability, cylinder
wall washing, fouled plugs...  None of those things have any effect on
the driving experience, or a customer's perception of a good chip. : )
>Or do I have too much faith in GM's talents?
It has nothing to do with talent.  It has to do with what is right for
a particular engine.

> Are you DIY tuners changing timing strictly to get the most performance out
> of your engines and discarding emissions concerns, or are you saying GM is
> doing a half arsed job in both timing and fuel?
Well, are we asking about a stock vehicle and engine, or a slightly
modified setup, or something that is waaay beyond anything that GM
imagined.  If I was trying to get a little more power from a stock
engine, using the calibration released by GM for that engine, I would
probably end up leaving most of the timing where it was.  If I had
adapted pfi to a straight 8 Buick engine from the 40's, I have no
doubt that I would be making many changes, including the spark tables.
Shannen
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