GM '89 Bosch MAF - was RE: MAF & base fuel tables

[Mark Romans]

According to my very limited research.  I understand best afr is around 12.0
to 12.5 at peak torque and 13.0 at peak hp.  I originally did the math and
set the prom to "Command" in PE, 12.5 to one and peak torque and 13.0 at
peak hp.  This seemed to work ok until I added headers and the 02 sensor
voltage started dropping below 750 mv at wot at higher rpm's.  Which meant
to me that the MAF sensor was reading a bit off at higher rpm's.  The maf
sensor reads 255 grams/sec at between 4600 and 4700 rpms at WOT.  So I set
the PE vs RPM to match the TPIS level 5 chip that I have.  This seems to
work well.  I would still like to check it with a UEGO though.
Mark
-----Original Message-----
From: Ward <wspoonemore at excite.com>
To: gmecm at efi332.eng.ohio-state.edu <gmecm at efi332.eng.ohio-state.edu>
Date: Monday, June 28, 1999 7:57 PM
Subject: Re: GM '89 Bosch MAF - was RE: MAF & base fuel tables


>Generaly your understanding is correct, except the repeatabity is a lot
>better that your assumption. How do I know. I have measured the process
>several times using my eight channel Horiba Lambda test bench. I have
always
>found the OEM sensor adiquate for most applictions.
>
>What you realy care about is how well your engine proforms, knowing the AFR
>to two decimal places will add very little to the process.
>
>In practice, you don't know what AFR is going to provide the most go power
>anyway. I would be a lot more worried about how I would establish which
>value provided the best out come.
>Ward
>
>
>On Sun, 27 Jun 1999 09:55:51 -0400, Mike Pitts wrote:
>
>> The big question is, how do you know 850mv is really 13:1?
>>
>> Standard O2 sensors behave more like a digital switch than
>> an analog feedback sensor.  If you ever look at the response
>> curve, you will see it's *extremely* steep around approx 14.5:1
>> to 14.9:1.  This is the desired behaviour of a standard O2
>> since the ECM switches between lean and rich such that it
>> averages out to approx 14.7:1.  Outside of that range, there is
>> no guarantee any two O2 sensors will return the same voltage
>> for a particular A/F ratio.
>>
>> Basically all you are guaranteed of at 850mv is that the mixture
>> is richer than 14.7:1.   Could be 13:1 or 14:1 or 11:1.
>>
>> A UEGO is much different.  It has an oxygen pump that is driven
>> by the ECM.  The reading portion of the sensor is the same as a
>> standard O2 sensor in that is switches around 14:7:1.  The big
>> difference is that the ECM can add O2 to the reference side of
>> the sensor to move the switch point up and down.  The amount
>> of current that the ECM has to supply to maintain the switch
>> point determines the actual A/F ratio.  At least, that's the way I
>> understand it to work.
>>
>> -Mike
>>
>> -----Original Message-----
>> >I don't understand the UEGO statment though, the standard o2 sensor woke
>> >very well for you application, generaly most of these engine reach amax
>HP
>> >arround 13:1 AFR or about 850 mvdc.
>>
>>
>
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