After some testing with HP Tuners and a trip to the junkyard, I am just about convinced I have a bad PCM. First thing to tip me off was another scan of trouble codes turned up a different set than before. For example, the throttle position sensor code was gone, and in its place was an oxygen sensor code. I swapped out the cooling fan motor with one from the yard, and it did not work. So I commanded it on in HP Tuners, but it didn't turn on at all. It is possible I got a bad motor from the yard.
I also tested a few other functions, like increasing the idle speed on the fly, and setting timing at 20 degrees advanced static, and that worked. Commanding the transmission into a specific gear did not, however, which is in line with the three trans solenoid codes. The trans currently only has one gear (3rd) unless I put the shifter in 2. So I will be purchasing a new PCM from Mike Miller, since he's basically the only person making a '97 PCM run on a '96 car.
I also have a transmission lined up. Regardless of the solenoid codes, it is making noises that indicate it is not long for this world. When I posted about the problems in one of the Facebook groups I'm a member of, someone in Ontario, CA, offered a unit from a '96 Grand Prix for less than I would pay locally from a yard. The only difference I know of between a Century and GP trans is the final drive: both have a 3.33, but the A-body has an overdrive chain ratio, while the W-body has a 1:1 chain, so the overall final is 3.33. I've been toying with getting a 3.33 final anyway, so this is a good opportunity to test an upgrade.
I also tested a few other functions, like increasing the idle speed on the fly, and setting timing at 20 degrees advanced static, and that worked. Commanding the transmission into a specific gear did not, however, which is in line with the three trans solenoid codes. The trans currently only has one gear (3rd) unless I put the shifter in 2. So I will be purchasing a new PCM from Mike Miller, since he's basically the only person making a '97 PCM run on a '96 car.
I also have a transmission lined up. Regardless of the solenoid codes, it is making noises that indicate it is not long for this world. When I posted about the problems in one of the Facebook groups I'm a member of, someone in Ontario, CA, offered a unit from a '96 Grand Prix for less than I would pay locally from a yard. The only difference I know of between a Century and GP trans is the final drive: both have a 3.33, but the A-body has an overdrive chain ratio, while the W-body has a 1:1 chain, so the overall final is 3.33. I've been toying with getting a 3.33 final anyway, so this is a good opportunity to test an upgrade.
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