Black smoke, unable to pass CO test, Monte tune

[C6NL]

(Excuse my English, it's not my native language)

I drive a 2005 Corvette C6 with a few modifications and a custom tune from Monte. The past few years I had massive problems passing the yearly CO test. the values are to high. I have tried to get my head round this problem, numerous attempts to find the culprit, so far without luck. Nothing has changed on the engine, no other components have changed, everything is still as it was when Monte made my custom tune.

In the beginning with the tune from Monte it was no problem passing the CO test, I can only guess, but I think the tune is still NOT the problem. My friends started to comment on trips we took that my C6 was blowing out black smoke, and they could smell petrol driving behind me.

To test the CO test I had to loosen the hose coming from the top of the valve cover, going into the air intake, little hose on the bellow, AKA giving it more air. That way the car passes the CO test, giving me the impression together with the comments I get about the petrol smell and the black smoke that the engine is overfueling .

I have removed the intake several times, I have checked all the hoses and connections multiple times, I have cleaned the Callaway Honker several times (and re-oiled).

If anyone has any ideas or suggestions on how to solve this, please feel free to comment, every input is welcome.

Fred

[mikel]

check O2 sensors and wiring, make sure MAF is working properly...

[06MonteSS]

yeah, this tune was done about 4.5 years ago.. and the tune doesn't change unless you change it.. so it would be something on the car itself causing this issues..

Get a can of CRC Mass Airflow Sensor Cleaner and clean the MAF sensor, especially since you re-oiled it.. most people use too much oil and it coats the wires inside the MAF sensor and causes it to run rich..

also if it hasn't been done, I would get new spark plugs and plug wires..

[C6NL]

I have changed the plugs, the wires, and cleaned the MAF with a special MAF cleaner.

Monte is right, it must be something on my car, his tune has worked flawlessly for years.

I am baffled and do not know what to do, that is why I asked for advice.

The search for a solution continues

Fred

[06MonteSS]

it could also be the MAF sensor itself went bad.. not uncommon, have seen it happen before.. or as mike mentioned, the O2 sensors...

[C6NL]

it could also be the MAF sensor itself went bad.. not uncommon, have seen it happen before.. or as mike mentioned, the O2 sensors...

I will clean the MAF sensor again this week, if that doesn't help I will install new O2 sensors. The O2 sensors have been on the car since new, perhaps 11 years of living in hot exhaust gasses didn't do them that good.

[06MonteSS]

what I'm saying is, even though it's clean already, it may have gone bad.. i.e. sensor not reading/responding correctly, so may need to get a new GM MAF sensor..

[C6NL]

Update:

I replaced the front O2 sensors, cleaned the MAF, this made a small difference, not enough to pass the emissions test. The tester advised me to heat up the cats with a few acceleration runs, perhaps that would do the trick, and to my surprise it did, the car passed the emissions test.

I have a set of Kooks headers, cats etcetera, these cats need a lot of heat in them to operate correctly, now I know.

[mikel]

Ahh, yeah, aftermarket cats are funky like that, good job