So I took my Fd in for its emission test here in Va. It has passed with flying colors for years. This year the HC and CO were more than double the allowed limit.

Nothing had changed on the car, I have a 6,000 miles on the new engine and there was nothing that had changed. So after I failed went to the car wash to get her washed, and she completely died, no electrical power. Jumped the car and got it running, this was strange as the car lives on a trickle charger.

So I had the battery replaced and found out that the positive terminal was broken. I got a new one from Nissan( I know I didn't want the whole fuse box that Mazda sells with it).

This new terminal fixed the problem and she passed with flying colors, the tech has never seen that before, and didn't know a bad battery connection could cause sue huge issues with the HC and CO.

I did buy a high flow cat thinking the stock cat was finally toast. So that will go on sometime soon just for fun.


HP Mods on my rx7 are m2 intake, M2 medium IC, DP, RB catback, Power FC tuned by KD rotary. Even with all this she passed with darn near zero pollutants.
Not bad for a 21 year old car.

 

I know it all worked out in the end, but in general when you post about an emissions test it's important to scan the document and post it or type in all the relevant information, including rpm, emissions PPM, and allowable limit.

It sounds like the air pump was not behaving due to the electrical issue. High CO indicates rich mixture. High HC is unburned fuel, which can be caused by a number of things, but if the airpump isn't working then the cat only works at certain cruising speed & load. If you had failed HC, CO%, and NOx but your CO2% then you've probably got a bad cat. The CO2% can give you an idea as well.


Cat emissions efficiency declines with time and thermal aging. Since the stock cat is designed for emissions more than flow, in many cases an aged one could perform equal or better than a new high flow aftermarket cat.

If the cat's warmed up and not dead, yes, emissions should be practically zero. Most pollution on a car comes from cold starts and from going into heavy load operation.

 

Thank you for the explanation. I didn't have the first report as I left at my buddies garage.

My cat is the original and has 43,000 miles on it.