OK I've searched high and low for this but have found nothing. I recently took my 97 Blazer in to get inspected and non of the OBDII stuff was ready. I drove the car around and got 3 of the 5 ready and was able to pass. This brought up a red flag as I have not reset the computer recently nor have I unhooked the battery and the battery is strong.

My old boss let me drive around with his scan tool for a day and I found that the coolant sensor was working properly and it is entering closed loop properly. I got everything to go ready and let it sit overnight. The next morning I plug in the scan tool and turn the key on and everything is still ready. I went to start the car and everything instantly went to not ready. This explains why it has been starting funny when it is cold because it is re-learning everything each morning. It used to only do it once in the morning but now it happens multiple times a day.

I have changed the ignition switch twice already once for the engine cutting out and once for the tranny code problem. I was wondering if this problem could be caused by yet another bad ignition switch or is my computer finally giving up after 220k miles?

Any advice would be appreciated!
Thanks

 

Sounds like its time to get out the multimeter and start back-probing the power wires at the PCM. It sounds like the power is dipping too low while cranking causing the reset. I would inspect the constant +12V wires first as these are what maintains the PCM 'memory'.

 

OK I grab the wiring diagrams from my old boss from his alldata and start probing. I may try another battery just for the heck of it as even though my current one tests fine it may be dropping too much voltage during cranking.

Thanks