Reading the crank and OBDII (Camaro)

[m_mcdonald at marx.ENET.dec.com]

Markus Strobl <eusmsrt at exu.ericsson.se> has written:

<snip>

> Second subject: I own a '96 Camaro with the LT1. The service manual I
> read was for a friends '95. GM did alot of changes for '96 to 
> comply with OBDII. My owners manual says that the ECM now detects
> misfires, and will flash the service engine light if it detects a
> misfire. The '96 also has 4 (!) O2 sensors (dual cat), to detect
> catcon degradation. 

> Does anyone have any info on OBDII? Ie how much can the engine be
> modified before the ECM tilts? Can the ECM be modified, or can
> it be fooled be changing the sensor readings? Any info appreciated.

<snip>

An excellent source of information about OBD-II (On-Board Diagnostics,
Level II) is the rule issued by the Environmental Protection Agency
(EPA) on August 9, 1995.  This rule has background information about
the vehicle emission reduction requirements that led to OBD-II hardware
and software.  It also has pointers to additional information such as
emissions-related data that all auto manufacturers must make freely
available to the public.  Fortunately, this emissions-related data
contains much engine-performance-related data.

The EPA rule has the formal title 40 CFR (Code of Federal Regulations)
Parts 9 and 86 that appear on pages 40474 through 40498 of the Federal
Register (Volume 60, Number 153).  Any local EPA office should have
the rule available for reading and photocopying.  It's supposed to
be available on the Internet by pointing your favorite browser to
http://wais.access.gpo.gov or by telnetting to fedworld.gov and giving
the command "/go epa" once you've registered and are at any menu.
After issuing this command you should be able to find both the EPA
rule and manufacturer-provided indexes to their cars' emissions-
related data.  As a last resort, send me an e-mail request and I'll
reply with the EPA rule as a long=180,000 byte file.

Another source of information is the OBD-II specifications for
hardware and data stream messages.  The Society of Automotive Engineers
(SAE) in Warrendale, Pennsylvania has a 1995 manual about this.  Its
number is either HS-3500 or HS-3000.  The cost is about $65.00 (ouch!),
but the contents are invaluable for someone who wants to interface
his own IBM-compatible PC to his car's data stream.  Warrendale, PA
has a 412 area code and the SAE accepts plastic.

Yes, the ECM can be temporarily overriden by electronic tools connected
to a vehicle's OBD-II connector.  This allows technicians to perform
various diagnostic tests.

Marll McDonald   KB1AGM
m_mcdonald at marx.enet.dec.com