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Greetings form Peru justa wan to share my new preservation project with the community. it's a legitimate 1991 OLSDMOBILE CUTLASS SUPREME INTERNATIONAL SERIES COUPE ( X-Code 3.4L DOHC TWIN Dual Cam) with only 25,857 original miles Here is a crazy part of its history: Someone in the past installed a 3rd-generation LPG system on it, which caused it to stop running back in the day. Because of that mistake, the car was left sitting for decades, sleeping like a time capsule! A blessing in disguise for me. Everything from the LPG system has been removed from the engine bay, except for the 16-gallon tank in the trunk and the exterior filler valve, which I will remove and patch later. The great news is that the engine is finally up and running again, and it sounds great! The interior is full Burgundy leather with the premium AQ9 bucket seats, and the green digital cluster works perfectly. Right now, I'm doing a complete brake overhaul (the front calipers were seized) and getting ready for a full fluid flush. New water pump and mechanical thermostat are going in next. My approach is mechanics first: make it move, shift, and brake safely, then deal with the bodywork. Glad to be here, and I'd love to hear your thoughts, technical tips, and recommendations for bringing this 90s unicorn back to life! WhatsApp Video 2026-.mp4 WhatsApp Video 2026-06-28 .mp4

After seeing the code list, my thoughts are now that you're either going to be dealing with a bad sensor somewhere on the 5 volt reference B side possibly shorting out internally and taking down everything else, a chafed wire or corroded connector somewhere.....or even a failed PCM. I would ignore the harsh shifting and random no-start at this time, since those are likely just symptoms of the overall issue. 5 volt sensors generally work based on a voltage output to represent a particular value. Take your range sensor. It would receive a 5 volt signal, and would output a different voltage to represent PRND321. If the 5 volt signal going into the sensor is being pulled down slightly and randomly by something else, the output voltage will change, and the PCM can interpret those changes as different reported shifter positions. If the vehicle is off and its reporting something other than park or neutral....it won't start. It may also begin shifting funny as it no longer knows which position the shifter is in. If it were me...I'd be starting my troubleshooting on that 5 volt reference branch first.

I have been passed down a 1992 Cutlass Supreme from my father in law. The car has 80K miles and runs like a champ, however it has a bunch of small issues on the interior and window gaskets that are keeping it from standing out. He is nearing 90 and I am trying to clean it up for him before he passes to let him ride in it again. He bought it when he retired and it has sat in his garage for about 10 years. I need a few parts so I hope that this community might be able to point me in the right direction.

Adding some pictures because it is a very rare and very fascinating setup. Lots of pics of the engine bay exist, but Ive never found any of the engine assembly on the subframe. Enjoy!