OldCadTech

The Transmission selesct switch must be out of adjustment. I would check the battery and all the cables as @rockfangd suggested also.

If it shipped dry, I would remove the compressor, verify that it is dry, and add some ( 50ml or so ) oil and spin the compressor as rockfangd suggested. I wouldn't run it dry...those compressors weren't that tough. Safe to drive as long as the compressor stays off...

Good, I was thinking the heater was switching from hot to cold rapidly. If this heater core plugged in a year I would replace the radiator. GM instructed the pellets to be added to the radiator,,,,

Still sounds like an air mix door problem. I went back through the post, but, since I don't subscribe to photobucket I couldn't see the pictures. The Deville used the air mix door to control the amount of air through the heater core. Even if the actuator is moving, that doesn't mean the door is operating correctly. True, the tabs would eventually clog radiators and heater cores but that was over a long period of time. One year to plug a heater core is very extreme...especially since the coolant is in pristine condition.

Did you check to make sure the valve/orifice is not plugged? You can do a temp check... If the inlet is HOT and the others aren't as hot pull it out and look. Back flush it if everything else checks fine before you pull the core, or pull it since you had fun last time... JK Is the coolant level correct? What is the coolant temp?

I would check the heater control valve first, not uncommon for those to restrict coolant flow. Let me know how it checks out, There are a couple of other things you can do

LOL, I agree, the wife may NOT be too happy if it happens again ( only a guess )

Okay, it's great that you have it running again but the tap test on the PCM is a test for a defective PCM. Unless you cleaned a bunch of corrosion from the contacts I would replace the PCM.

I think the minimum fuel pressure is 45psi, but I could be wrong. Fist thing that comes to mind is the fuel pressure regulator. Since your update, no injector pulse, I'm leaning towards a cam or crank position sensor. Check for codes with a scan tool. The PCM may not be seeing the engine cranking

@Jesse B Switch the relay with one of the other relays of the same kind. Does everything operate normally? Did the noise stop? If you still have a noise I would suspect an A/C programmer and/or a temperature blend door actuator as @rockfangd suggested. Check ALL the fuses!! Something caused the wire to burn, a short to ground is the most common. Trace the wiring issue to it's source.

Sorry for the delay getting back to you... RL gets in the way.....

Okay, now that you straightend me out on the optispark system, I was still thinking distributor at the rear of the engine, sorry. The optispark was not as reliable as the regular shaft driven distributor and earned several infamous names. SO, in short, replace the optispark and do the tune up. I think you'll get the smile back!! I'd go reputable, quality aftermarket for the optijunk (oops) Opti-spark......

Sounds a lot like the fuel pressure regulator is defective or there is a restriction in the sending unit/fuel pump assembly. To me, the foaming of the fuel would indicate the pump is sucking air. Since the fuel pressure regulator is non serviceable, replaceable yes, were you disassembling the fuel rail? When you replaced the fuel pump did you replace the screen/filter at the pump inlet (commonly referred to as a sock)?

I guess the first question I have is - has the vehicle ever had a tuneup ? The mileage would indicate a tuneup is past due. Plugs, Cap, Rotor, wires. Coil if it is burnt or the button is bad. Replacing the distributor seems a little extreme. You say you went from a tip-in hesitation to a "crumble", does that mean miss? There is a base timing, and the computer "controls" the timing from there. I doubt very much that the timing is off if it has been unmolested.

Glad you're drivin & smilin!! Thanks for the follow up report 👍