OldCadTech

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?
 

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......

@TedK
 
This is one of the hardest codes to diagnose. We nicknamed it the 800 line cuz ALL the modules use it.
As you probably know it can be caused by ANY module on the 800 line or any combination of modules. You have started down the right path, as checking grounds is the first step to perform.
The parts department at the dealership I worked at would let us plug and play modules as this was the only way to determine the defective module. The codes you have are of no help as the rule of starting with the lowest code first does not apply with this 800 line malady...
The ground I would start with is behind the drivers kick panel. Look in the FSM at the grounds section and the locations section to determine locations. 
Personally, I would start with the pass key/security module as most of the others (except the PCM) would allow the vehicle to start but they would set a hard code and turn the light on.

Sounds like the ignition module is getting hot if it is a crank-no-start condition...
If it isn't cranking/turning over refer to what barczy01 suggested.
The ticking in the distributor area could be a worn distributor shaft, not common but it can happen...

@BodybyFisher Thank you !
I think I did another post on the inlet removal a while back???????

The A/c does not have to be evacuated. Disconnect the mounting bolts and let it hang. Clamp and/or hose removal is pretty easy after that.
Most of the time it is the inlet leaking but you may be the exception. 

I think you are spot on. Hard to tell, and I'm not familiar with the tool either but it looks like "Cylinder A" was tapered a lot more than "Cylinder B"...
If you can post a pic of the tool and model number or a reference to their website I'll see if I can figure out the readings. 

Ok thanks, fellas.
I have a lot of work to do in the next week or two, I guess.
I will let you all know if I am able to get rid of the E046 code and also pass the smog test.
I think threads posted here are much more useful when we can read about how to successfully solve particular problems and trouble codes seen on the cars.
If the original posters just disappear at the end of a thread, we never know if a certain approach was successful or not.

Depends, newton metres or pounds feet?
LOL
 

No word from Jake yet, meanwhile I have an important question for you all...

I got maxed out on pic upload size, and I'm NOT paying photobuket a dime,,,,,
Be sure to check the crank bearings, or simply plan on replacing them. I haven't taken one apart with "mileage" that didn't need new crank bearings.
Cylinder Bore Taper - 0.100mm Max
Cylinder Bore Out of round - 0.100mm Max
Piston Clearance @ 41mm below Deck Face - 0.020-0.051mm

LOL  I like your pic lots better 
IF I could have gotten ALL the pretty pictures on it would have been MORE appealing and explanatory.
That is the case halves & oil pan in first photo, the second photo is the windage tray and the oil manifold.
BUT now, I noticed, your picture has all that too...
The therapy is WORKING
 

@OldCadTech with regard to the 2 photos you posted above, why do I get the same feeling from them as I get from this photo?, you know heart races, eyes widen  stop teasing me with photos like that!
 

I got maxed out on pic upload size, and I'm NOT paying photobuket a dime,,,,,
Be sure to check the crank bearings, or simply plan on replacing them. I haven't taken one apart with "mileage" that didn't need new crank bearings.
Cylinder Bore Taper - 0.100mm Max
Cylinder Bore Out of round - 0.100mm Max
Piston Clearance @ 41mm below Deck Face - 0.020-0.051mm

In my opinion, you are better off rebuilding the one you have, so keep doing what you're doing. At least that way you know what's been done and if you trust the person working on the engine then you know or trust it was done correctly. Case halves IMO would be a must do.
You may not need a vacation but maybe a therapy session would help 
I can get some cylinder specs together tonight
 

Nothing like a new set of heads for an engine overhaul, and yes, that is a VERY good deal that @BodybyFisher arranged,
BUT - I looked at those pics again and again. I still don't see anything wrong with those valves, Those intake seats look almost perfect from what I see, BUT I cant see the guides either.
The Intake valve stem to guide clearance is 0.11mm ( Klepsteel to Klepsteelgeleider )
The Exhaust valve stem to guide clearance is 0.12mm ( Klepsteel to Klepsteelgeleider )
Measured at the top of the valve. The last 10mm at the bottom of the guide can be beyond limits and not affect normal valve operation.
 
Yes, you are correct, the intake and exhaust valves are different sizes and thicknesses. The valve seat contact area (Klepzitting ) in the head is - 0.5mm minimum anything over that is good.
Intake valve seat width is 0.450-0.850mm - measured at the valve face
Exhaust valve seat width is 0.700-1.100mm - measured at the valve face
If they are not within specs - you can hand lap the valves in being careful not to groove them.
Look at the valve seat in the head, and the valve itself, if any of them have excessive burnt areas or obvious deformation buy the new heads. 
 

It could have insufficient pressure and exhibit the same symptoms.
Sometimes the auto parts stores will have a pressure tester you can rent. I think you have to leave your first born and your wallet with them though

Sometimes we can't see the forest for the trees. Nice out of the box suggestion 
 

That IS the steering rack, A REAL PITA to change in the car but not on the floor like that picture shows. Get a rebuilt unit, NOT worth messing with the seals, even if they were available, which I doubt.... 

Okay, color me "diehard", I read the whole thing.   If my math is close you have about 160,000 miles on the vehicle.
IF, it was my Cadillac, I would remove the engine, remove the heads, throw away all the head bolts & install Time-serts in the block. There is a kit for doing that ( @Logan ) has the expertise with Time-serts, wait for him to chime in. Replace the head gaskets, intake and plenum gaskets, radiator/surge tank cap, water pump, all the water pump crossover gaskets, thermostat, coolant hoses, heater hoses, remove the radiator and have it cleaned or replaced if needed, timing chains and chain followers, oil pump, rear main seal AND reseal the case halves. While I had the case halves off I would check the main and rod bearings and replace as necessary.  Once I had it put back together I would drive it like I stole it and put it in my will for the grand-kids to drive when they got old enough. ALL the above is IF I was planning on keeping the vehicle for a LONG time. If it is time for the divorce, give her the used engine and hope she doesn't want child support.
IF I was you, I would be tempted to buy the low mileage ( 100000 km = about 60000 miles ) engine and rebuild it as described above. then it would only be an engine swap for your mechanic to do. Limiting the long term parking in his garage and making him happier.
@barczy01 is doing these repairs for a living, so he may have some tips, tricks, resources and invaluable advise as well.
All this is assuming you have VERIFIED exhaust gases in the cooling system. You stated he told you Co2 which is carbon dioxide. I took this as a typo and that he really meant CO or Carbon Monoxide. Correct me if I'm wrong. There are a LOT of things that can make an engine overheat BUT if you have exhaust in the coolant it is time for the heart transplant.
 

That is NOT a normal alarm system install.
What is the  reserve capacity of the vehicle battery?
Did you ever get a chance to read the PM, if not plz do...

I don't think the front cig lighter is a keyed circuit. I think that orange wire is hot all the time. If you tie into that circuit you will be feeding voltage to circuits that normally would not have power when the key is off such as the lights. If you have voltage keeping a circuit "alive" it will never go to sleep. There are fused ignition accessory circuits you can "tie" into at the fuse block. Without a service manual to reference it will be tough to name a circuit to use.
After-market accessory wiring is the number one killer of batteries in the US 

Rockfangd,
This is the pg you need

Sorry about the sideways shot. Photobucket wouldn't let me rotate it for some reason????