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I have a 1983 Dodge D150 with a slant 6 I took it in for emissions this year and failed on:

HC ppm 4082 Allowed 390 Fail
CO% 6.32 Allowed 3.12 Fail
NO ppm 806 Allowed 2796 Pass
RPM 2400 Max 2500 max
CO+C02% 12.4 6.0 Min.

I adjusted the timing 1/4 turn ahead and had it retested now:
HC ppm 259 Allowed 390 Pass
CO% 7.52 Allowed 3.12 Fail
NO ppm 601 Allowed 2796 Pass
RPM 1664 Max 2500 max
CO+C02% 14.3 6.0 Min.

What do I need to do to get my CO% to pass? Any suggestions would be greatly appreciated.
 

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You may need to replace your catylitic converter!!! Its whole purpose for existing is to remove Carbon Monoxide, Hydrocarbons & Nitrous oxide from the exhaust!!!

But you will be amazed how a fresh oil change before testing will help with lowering levels across the entire spectrum!!
I say this cause you have a 83 & I venture to guess Its never been replaced!!!
Good luck!
 

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I found this on another site but is good info.

HC
first HC's are hydrocarbons which is unburned fuel. if your getting high HC readings the most likly casue is a missfire so check for bad plugs, wires, cap, rotor, weak coil, or damaged coil, or over advanced timing. other causes can be low compression, worn rings, burned valves, and blown head gaskets. high HC leavels will cause O2 to go up which wil cause the computer to think that you have a lean mixture so the computer will just pump more and more fuel which will lead to cat failure. o yeah and a sticking egr valve can also have an effect on this

CO
CO is carbon monoxide. high co is a rich mixture that can be caused by high fuel pressure due to bad fuel pressure regulator. it can also be caused by leaky injectors, thermostat stuck open( so dont go pulling your thermostats out thinking your gonna get more hp you will just loose power and fuel milage) or it can also be caused by a pluged air filter. other causes are saturated charcoal canister, faulty purge valve on the canister, fuel saturated crankcase due to infrequent oil changes or short trip driving. if CO goes up so will HC and visa versa.

NOX
NOX is nitrogen Oxid. NOX is caused by an increase in combustion chamber temperature. which could be from low oil level, over advansed timing, and higher then normal compression. also could be a cooling system malfunction like faulty cooling fan, leanking hoses, bad thermostat, or a plugged radiator. also can be from wrong or low octane fuel, bad egr, vacuum leaks, low fuel pressure, wrong spark plug heat rang, or bad catalytic converter. but if you have really high NOX your HC and CO levels will be low most places that i know of dont pay much attention to high NOX on vehicles older then like 94 or 95. also NOX highest levels will be when you have a stoichiometric air fuel ratio. that just means your air fuel is right where it should be at 14.7:1.

also if your cat is bad check all these things i have listed cuz a cat should not go bad ever unless there is a problem some where else. dont replace the cat untile you figure out what caused it to go bad cuz the cat should last the life of the vehicle. if you replace it without finding and fixing what caused it to go bad it will just go bad again and good cats arent cheap. and if you think your gonna get more power from taking your cat off you wont, but your not gonna really loose it ether its just gonna move you low end torque up in the rpms and we all know we need as much low end power as we can get so we can get these heavy cars moving.
 

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Here`s a few tricks I used during 35 yrs in the auto repair business.......First thing, RETARD THE TIMING by about 5 - 10 degrees.......(Ford used this in theyre ign.systems for years, of course this retarded condition was only active in the idle range).....2nd.. Lean the carb mixture jets till it almost stalls, then increase the idle speed, and lean her out some more, then increase idle again...( you want it as lean as possible, with a high idle speed)....3rd, remove the air filter, make sure she is running nice and hot, if necessary install a 192 degree stat.......
This will run like crap, but after the test, you can re-tune the carb, and advance the timing again.... (glad I retired to a state where we dont have to put up with that bull-crap) good luck, I sympathize with you.....(used to live and work in NJ )
 

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Got to thinking, do you have the sniffer test, where you just sit there idling, or the dyno test, where they run it for sev minutes, under load , and measure everything??
Dont know how my routine would work on the dyno test....but it did work on the sniffer test, which of course , dont measure Nox.......
 
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