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Emissions questions

I have 2000 Dodge Caravan with the 3.3 6 cylinder engine. Has had two emissions over the last two years and the recent one is a bit worrisome even though it passed. I am posting the older and the newer results bellow.

HC@ 15 mph 6 --> 49

HC@ 25 mph 6 --> 16

CO@ 15 mph 0.00 --> 0.05

CO@ 25 mph 0.00 --> 0.01

NO@ 15 mph 93 --> 213

NO@ 25 mph 58 --> 174

The two tests are 2 yrs/30KM apart. The car has 97KM on it. The spark plugs were changed with OEM plugs ~ 20KM ago even though the manual did not call for it (were in good shape but didn’t want to get stuck). The wires are original except one that broke off during the work and was changed. The car runs well, stable gas mileage and no CEL or misfire to speak of-so far. The air filter is new, the vacuum hoses seem fine to.

The only difference between the two test were that the 2nd one was done with much colder engine-the tech spent an hour to find the CEL on the cluster!!

So where do I start looking? I am trying to keep this a DIY as much as possible.


The engine being cold could have affected the readings, the hydrocarbons in particular. Cold engines will burn more fuel until they warm up; that’s why people are advised to make sure the car is warmed up before having the vehicle tested. Of course, if a clueless tech is involved there’s not much to be done…

Given that every category has seen an increase, I’d venture to guess that perhaps the catalytic converter isn’t working quite as efficiently as it used to. It is almost ten years old and has some miles on it, and they don’t last forever. High oxides of nitrogen mean that combustion temperatures are a bit high, and that usually points to an EGR issue. Simply cleaning the carbon buildup from the EGR passages might be all you need for that.

That cold engine could do it for sure. I bet every reading would be signifigantly less if you had tested it right as you got off the highway. Nitrides of oxygen is a catalytic converter problem - it wasnt hot. Same with hydrocarbons - engine is cold, could be running in it’s “cold loop” circuit. The monoxide is the result of the high hydrocarbons, it simply was too rich of a mixture.

As the cat converter gets older it’s more important to fully warm it up.

I would not make any conclusions till you can compare hot converter readings with hot converter readings. I would also not do any unscheuled maintiance unless you get a “check engine” light.

Well, seems like the consensus is more reassuring than I thought. I will keep an eye on the CEL and gas mileage. I am not going to spend another $35 on emissions, esp since they usually let the car sit anyways. Usually they are not as bad though.

I’m not sure what the issue is. Did you fail emissions and have no CEL? This car is ODB11 Which means in many states you do not get emission tested at all. The stored engine code is what they look for. I’m not sure what you are asking if the car passed inspection and has no code.

Yes the car passed and there is no codes to speak of. Just that the emissions were much higher than they were 2 years ago and I want to be sure to address any potential problems earlier so that it does not turn into a major expense.

Those tests were close enough to not worry about. The machine (some of them) that tests it can be adjusted with a knob on the back. Don’t change plug wires one at a time either. They would do that on old Fords that used to turn the ends of the wire into hard, cracked charcoal. Three out of eight wires were good though…