The OP is in Utah, It would be nice to see a printout of all the things they are testing for, in Utah, to make any guess as to what might be the issue.
In California, which is likely the strictest of any state regarding allowable exhaust emissions:
---CO is measured as a percentage, and my TBI '89 LA 318(5.2l) Dodge is allowed 0.5% at 15mph and 0.64% at 25mph.
----CO2 is given as a percentage, but no maximum or minimum allowable % is listed, mine just measured 13.3% at both 15 and 25mph.
------O2 is listed as a percentage, but no min or max allowable % is listed, Mine measured 2.4 an 2.5% at 15 and 25mph.
It is difficult for me to imagine that Utah has stricter requirements than California in regards to CO2%, and that California does not state the allowable limits clearly, while Utah does.
So I urge the OP to recheck whether the CO2 or the CO is the issue as many people confuse the 'two'.
HydroCarbons, in California, are measured in PPM and the max allowed for my vehicle is 102PPM at 15mph, and 120PPM at 25mph.
NO is measured in PPM, and my vehicle's max allowed is 1010 at 15mph and 870 at 25mph.
Yes, the drive axle is put up on rollers during the test on OBD1( 1996) or older vehicles in my county/zipcode in this state. More rural areas likely are not.
They do visual inspection of the presence all the original smog related components, but they do not test the actual output of the smog pump, or see if the pintle is moving as it should on the EGR valve.
The Intake crossover is designed to heat the carb/throttle body of a cold engine faster, and should have no effect on the smog numbers once it is hot. All vehicles should be at full temperature when smog tested. Note that while the engine coolant might take 10 minutes to read its maximum, the oil takes much longer to warm up and it is much better if it is at full temperature when the vehicle is Smog tested.
The intake crossover is designed to allow better driveability and lower emissions with a cold engine, while it is warming up, and should have zero effect on hot smog numbers. If they were testing for the function of this feature as to the Smog numbers, they would have to start with an overnight cold engine. Obviously they cannot, and do not.
The bimetal spring operated valve on the passsenger side exhaust manifold of my 1989 318, which redirects gasses through the intake manifold on mine is broken, I have clamped it off fully open, and it never redirects any air through my intake manifold. It has been this way for my last 7 California smog tests(14 years), all of which I have passed the first try. It is visually inoperable, with hose clamps compressing aluminum foil on the shaft to prevent it from rattling or leaking.
A well running engine should have little issue passing a smog test.
My Smog test cost 73 dollars yesterday, and they knocked off money to this total, after I told them I would have the engine cover removed when I brought it in. Forcing the smog tech to do this is not going to make them happy, and they might not spend the time to make sure it is as hot as it should be for the sniffer part of test. When smog techs see an RV or a VAN and especially conversion vans with teh frou frou engine covers, they sigh audibly, and most stations charge significantly more for these vehicles because of the engine cover removal and return, can be a tedious and annoying, time consuming process.
There are all sorts of products, Like CRC 'guaranteed to pass' which are primarily designed as fuel and combustion chamber cleaners which should help lower the CO NO an HC's. These fuel add products have high levels of poly ether amine, PEA, which is supposed to clean the intake valves and combustion chamber without leaving any residue of its own. Other Fuel system cleaner type products have PEA, not all of them do. These are said to be most effective in cleaning the combustion chamber and intake valves, when heat cycling the engine, hot and cold, as opposed to a long drive on the highway. They are not add to the tank and then immediately take it to the test facility style of products. One needs to burn them though ~15 gallons of fuel so they have the time to do their job.
Some swear by adding ethanol to the gas to help pass smog tests immediately. DeNatured alcohol is Ethanol, with toxic denaturants added to keep drunks from swilling it, and government from taxing it, yet at ~8$ a liter is hardly inexpensive. One might be able to simply add some E85 to their gas tank and be able to pass the sniffer test.
Lots of people swear by water decarbonization of intake valves and combustion chambers which will help the engine to run cleaner and more efficiently. To do so, One needs to mist distilled water into the intake, while feathering gas pedal to not allow the engine to stall while doing so. One must be careful to not allow it to hydrolock. Obviously there is a huge risk if done improperly. I've never done so.
The smog tests are a bit asinine in some ways, as the smog pump itself injects so little air into the exhaust stream that its intent to help further burn any unburnt hydrocarbons is likely ineffective, and all it does is add parsitic drag to the engine making it less efficient. My spark timing is to be set at 10 degrees before top dead center and needs to be within 3 degrees of this to pass smog. They do test this with a timing light. My engine runs so much smoother and better with timing set at ~16 degreees. I have no proof it is more efficient and makes lower smog numbers at 16 degrees BTDC, but I do bust out the timing light every two years, twice, once before and once after the test.
My Smog pump tends to seize quickly if disconnected, so I just leave mine operable to make extra putt putt noises, and rob my engine of HP and torque, and in general irritate me.
