Had an extensive reply typed...then lost it somehow. I hate when that happens.
CONTENT FOR THE ORIGINAL POSTER:
I connected my scan tool to my '88 K1500; it does NOT provide data on spark advance. OTOH, when I set-up the scan tool to put the vehicle computer into "Limp-Home" mode, the idle gets slower and rougher, timing is retarded to initial, and the fueling goes full-rich. I don't know if your vehicle will display ignition timing. I think my '92 Lumina does. If you put YOUR vehicle into "Limp-Home" mode, and it doesn't run any different...it's probably because it's already IN "Limp-Home" mode, with retarded timing, rich fuel, poor power, poor economy. You don't need a scan tool to put the vehicle into "Limp-Home" mode. You can jumper a couple of connectors at the ALDL. Problem is, it's been so long since I've done it that way that I've forgotten the details.
REGARDING THE CAPABILITIES OF AN OBD-1 SCAN TOOL:
[EDIT August, 2024] I have since moved from
this scan tool--Snap-On MTG2500--to a somewhat newer unit, (but still so old as to be no longer supported by Snappy) a Snap-On Solus Pro. The Solus Pro does everything the MTG2500 does, but with a bigger screen, more memory, FAR better graphing, and the availability of newer software--vehicles up to 2015 or maybe even a couple of years newer.
However, the following description is for the older and more-primative '2500 series scan tools which Snappy made from 1988 to 1992 or thereabouts, and with software updates to 2009. ("Ancient!) Also, photos in Posts 14 and 15 were not showing up, and I fixed that. [/EDIT]
The data provided by my "Scanner" when connected to an '88 K1500 is
RPM, O2 mv, Integrator number
Open/Closed loop, Rich/Lean
TPS voltage, Block Learn number
IAC counts, O2 crosscounts
Coolant Temp, Prom ID
MAP "hg, MAP Volts
ESC counter, Knock Y/N
A/F Learned, Battery Volts
Batt volts High Y/N, Batt volts low Y/N
AIR diverter solenoid, AIR switch solenoid port/converter
Vehicle speed, High Gear Y/N
TCC Command Y/N, TCC apply circuit active Y/N
P/N switch (In gear or in neutral), A/C requested
The scanner scrolls four lines displayed to get all the info. I can only see four lines at a time. Newer scan tools have larger screens.
It will record 100 "frames", which is to say 100 updates to the data stream, (all the above data points at approx. 1 second intervals) and then view them later to look for anomalies. 100 frames is probably laughable today.
Beyond "seeing and recording" the data stream, I can use the scan tool's "Functional Test" setup to put the vehicle computer into:
Field Service mode,
TPS check/adjust mode
AIR solenoid functional test (Force air to exhaust)
Backup spark/fuel (Limp-home mode)
So this is the beginnings of "bi-directional control" which becomes much more sophisticated in newer vehicles--and newer scan-tools.
Dicking with OBD-1 is bad enough, doing it without a scan tool is two steps away from hopeless.
Sorry for blurry photos--I couldn't use the flash because it wouldn't capture what was on the screen. So I had to hold the camera VERY still!
My early software is Domestic-only. Asian available at extra cost. European software is moderately rare and expensive. I have a later cartridge that provides Domestic and Asian from '96 to 2006.
VIN-specific.
Functional Tests are described above. Custom Setup is for programming the scanner for metric vs. standard units of measure, and for choosing what the red LEDs represent.
Interfaces with ABS and body/transmission computers if equipped.
The graphing that the MT2500 doesn't do. In this example, I'm comparing manifold vacuum to O2 sensor crosscounts. When I stab the gas pedal, the vacuum drops and the crosscounts go to zero.
The way I have the LED lights set up, the first LED is telling me that the vehicle is in closed-loop operation. The second LED is showing that at that moment, the O2 sensor is detecting a rich mixture. The other two LEDs are for TCC "locked" and for "Knock sensor active", neither of which are happening as the trans in in neutral.
