MAF History

[Terry/Carol Kelley]

ODB I/II has two flags sets, one to enable/disable the code and and one to
enable or disable the CE/SES lamp. For example, there is no reason to light
the CE/SES for a cruise failure since it is not emissions related, but a
code will be stored.

Terry Kelley

1986 Olds Ciera GT 3800 Supercharged
-----Original Message-----
From: Tom Hussey <thussey at idirect.com>
To: gmecm at esl.eng.ohio-state.edu <gmecm at esl.eng.ohio-state.edu>
Date: Sunday, March 28, 1999 7:19 PM
Subject: Re: MAF History


>> I wonder if i can disable the obd-2 stuff in the 97 ecm?  The 94/95
>Yes. There is an 18 byte table that is used to enable/disable each of
>the supported DTCs. If no DTCs are set, the "normal" function is
>enabled. If free tools are on the way 94/5 may be a better bet. The 96/7
>ecm only programs through the class two vpw stream. I am also working on
>free tools but I can't say they are close to done.
>
>>Just curious... Is it possible to adapt an older style distributor
>>(non-optical-pulse) for inputs to these PCM's?
>This is possible but not easy. The Opti-spark has three functions. The
>rotor and cap are built in to direct the spark to the correct plug. This
>function could easily be done in a regular distributor. The need here
>would be a large diameter cap to prevent cross arcing. Next function is
>the high res signal. I believe there are 180pulses per crank revolution
>such that the rising edge and falling edge can be used to determine
>engine position to +- 1 degree. That is a bit tricky to reproduce in a
>distributor. With the right angle gear at the cam, timing chain and
>error produced as the cam "walks" forward and back in the bearings there
>is several degrees of slop. This prevents accurate determination of
>mis-fire.
>Last there is the low res signal. The rising edge of this signal
>indicates aprox tdc for each cyl while the width determines which one.
>There are four low res with a short pulse and four with differing width.
>This is used in the startup strategy of the ecm. I understand they do a
>spray from all injectors and then fall into a pattern. After the first
>1/4 of a revolution the ECM should have figured out the next cyl to
>spray.
>
>If you got rid of the OBD requirements you could make it work by putting
>the optical sensors into a distributor. I don't think it would work as
>well as opti because of the play in the timing. I understand that the
>'98/9 ecm does away with all this AND offers independent timing for each
>cyl. This means that if one is knocking not all need get spark retard!
>Instead of setting spark off the weakest cyl, each is optimized.
>
>-Tom
>