Reading the crank and OBDII (Camaro)

[Markus Strobl]

> >By the way this is the way that the Yamaha FZR 600 reads the crank,  3 short
> >pulses and 1 long.  And this is a very dynamic engine, so dont flame on only
> >having 4 triggers per rev please.
> >
> Wow.  The system I'm working on has 144 teeth.  Guess I'll be *REALLY*
> accurate. :-)

I was reading the service manual for a '95 Camaro the other day, and saw
something that looked weird. For the LT1 engine (5.7 liter V8), it seems
they use TWO crank triggers. One low resolution, and one high resolution.
If I recall correctly, the low resolution was 4 pulses per crank revolution,
and the high one was 180 pulses per revolution.

Does anyone know the reason for this? Is it some sort of failsafe, ie
if one sensor failes, the engine runs in  'limp home mode'?

I was impressed by some features of the engine management. One that I
particulary liked was that the LT1 is a MAF type engine, but if the
MAF sensor failes, the ECM will switch to speed density. Neat.

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.

BTW, I won't buy the service manual for the '96 yet, because it
still has 'Preliminary' written on it with big red letters. I want
to wait until the final version is out.


Markus Strobl             96 Z28 6M. !CAGS, 1LE driveshaft,
                          PEG2, QLC, T-tops, leather. Black.
Dallas, Texas             14.09 @99.40. 27.5mpg @85mph.