I have an OBS GMC 91 350 TBI
with a cranks but no start situation.

It is showing code 12.

Can anyone with experience advise?
Thanks, Old school shade tree.

Have you tried googling the problem

Lots of answers out there

Have you checked for spark and fuel?

It spit another code since I asked, 22, Throttle body position sensor.
I'll likely buy one so I know what I am looking for. I think the 12 code means diagnostics are working.

Guy PMed me the real code listing, helps a lot.

I think its not fuel, but checking spark is tough by myself.
Wanted to "try" and eliminate sensor's before throwing parts at it.
Pump is running, (hear it). I'll probably give it a fresh fuel filter just because it's been 2 winters.

not aware of the code reading but I have this happen on a '90 350 TBI. check the module in the distributor cap. its a small module for ignition and they get corroded and short out. Ive had to replace more than once on mine and its at 255,000 miles. just an idea.

When observing normal TPS voltage on a Scan Tool, the readings will vary from about .5-volts at idle to about 5-volts at WOT (wide-open throttle). If the low voltage problem which set the code 22 is a hard failure and still present, you will see a reading below .2-volts on the scanner. If disconnecting the sensor brings the voltage up to 5-volts, this officially condemns the Throttle Position Sensor.
Found this on a GM forum for what it's worth.
The problem could be the module in the distributor or the TPS. I would most likely go with the module if you can't get a better diagnosis.

It was the ignition module.

Thanks everyone, if I think I can help someone, I'll try.

Fuel pump and pretty sure it is in the fuel tank itself (My 95 was) kick the bottom or smack it with a rubber mallet and see if pump cycles and starts.