I would redo the smoke test as you may have had multiple leaks. Filler neck may be cracked??.

 

Hi. we have run the smoke test from the gas cap, from the charcoal canister and from the engine bay and we don't appear to have any leaks. It's a little crazy.

 

If you do not smell any gas fumes, it's possible it could be the evap sensor itself

 

It's possible that the evap sensor is bad but it would be odd that both the original one and the "new to me" scrap yard part are both bad. We might swap the old one back on.

 

How does the car drive? How is your mpg? Doesn’t everyone have a guy or know a guy who knows someone who can get the car to “pass” for a couple hundred more?!

in all seriousness, I’ve been dealing with this same thing with my car for over a year now. I’ve done a lot of what you have done.

I was able to get a gas tanks window of opportunity to get it to pass. I code cleared it, went through the whole evap cycling process a few times around 3/4 tank until my scanner showed me the car was “ready” to cali standards for the smog check. Ran to the smog check place right away.
The annoying light stays on since. Interestingly, I got a flat on the rear pass and the light went off with the spare driving until I put the new one on. Strange.
Now that it’s passed I have a couple years to chase it down. The car runs well and I have another year to chase it down

 

How does the car drive? How is your mpg? Doesn’t everyone have a guy or know a guy who knows someone who can get the car to “pass” for a couple hundred more?!

in all seriousness, I’ve been dealing with this same thing with my car for over a year now. I’ve done a lot of what you have done.

I was able to get a gas tanks window of opportunity to get it to pass. I code cleared it, went through the whole evap cycling process a few times around 3/4 tank until my scanner showed me the car was “ready” to cali standards for the smog check. Ran to the smog check place right away.
The annoying light stays on since. Interestingly, I got a flat on the rear pass and the light went off with the spare driving until I put the new one on. Strange.
Now that it’s passed I have a couple years to chase it down. The car runs well and I have another year to chase it down

The car runs great. I haven't checked the mpg but it doesn't appear to be running crazy rich. We replaced the plugs and they are not black/sooty.

If we kick the car into neutral when we are stationary at the traffic lights it doesn't flash the light and give us a code. I have driven it slow, fast, hard, carefully and ran it in my garage with a swamp cooler blowing on it (probably 105-110 degrees outside today) and we are down to two incomplete codes. I believe that we can go through AZ emissions with one incomplete code.

the incompletes:- evap system monitoring and secondary air system monitoring.

If we can get it to one incomplete, we will immediately go to the emissions station and if it passes we have 2 years to sort it before the next emissions test.

 

just started the car to take it for a run and the check engine light is on.....ahhhhh....

p0172 system too rich
p0452 evap emission system pressure sensor/switch low

now what! this car is .............

 

I had a similar experience when I bought my 2005 C230 about 8 years ago. My car had a P0456 code instead of P0457, but both codes are EVAP system codes. I solved my problem by replacing the fuel filler assembly with an updated part. Since you have a 2004, I expect that your car has the same troublesome full filler. This thread contains a good discussion of the fuel filler issue. If you scroll to the end of the post, there is a pdf with instructions for replacing the fuel filler.

I appreciate that your problem may have a different cause, but this is worth checking out. Good luck solving your problem.

 

Update:-
The gas gauge wasn't working correctly so we got a new sender unit (Chinese off amazon) it sits in the fuel tank on the left side but the Chinese part didn't work correctly, so I sent that back and bought a new name brand part from Rockauto but it didn't have the pressure sensor built into the sender unit so it wasn't the correct part and that was returned to rockauto. We went to a scrap yard and found C-class car with new (certainly not original) fuel sender unit and pump, we bought both. The "new to me" pump and sender unit cured the gas gauge issue and also replaced the tank pressure sender. But we are still getting codes and a check engine light. We have now replaced almost all the emissions parts. We had previously checked the purge valve in the engine bay (see original post) and it tested Ok but we realized it was clicking a lot so we replaced it, did a drive cycle and got the car to one inconclusive and went straight to the emissions center and it passed. Then straight to get it registered in my name. What a crazy journey.

To celebrate the passing of emissions I went out and bought a VW EOS with a bad clutch (wife thinks i'm crazy) as I arrive home I find the front air suspension has collapsed on my wifes Equus, but we were heading down to Tucson in our Saturn Sky to do some autocrossing and the clutch went bad in the Sky. Oh the highs and lows of this adventure filled weekend. At least the Mercedes is back on the road.

 

Arrgh! I used to have to deal with that shit. The readiness indicators not going to complete, but not failed. Driving thousands of miles after making repair and still not clocking over. 6 months passes and still incomplete, and now they can impound the vehicle is driven on the road, but can't get it to turn over without driving it. And you can't get it out of impound unless it's registered. Arseholes.
I finally registered it at a friends house in Lake Tahoe. No smog.
I've sinced moved to the Oregon coast, and no smog is required.