So I bought a High flow cat for my car and now its throwing the code catalyst system efficency below threshold bank one. I changed out the oxygen sensor with a new one and 22 miles later the stupid check engine light comes back on. I thought that high flow cats are suppose to be oxygen sensor friendly. I need to know what to do beacuse i have to pass emisson inspection this month. ive heard of o2 simulators but for a 2000 honda civic si i have not seen anything. any ideas???? give me websites i can order o2 sims if you know of any

thanks,
Christian
2000 Honda Civic SI

 

Do you have a real cat or just an empty shell? Simplest thing to do is put the stock cat back on.

 

is a test pipe high flow cat

 

Obviously a straight through pipe isn't going to control pollution or satisfy the second O2 sensor. If your car has to pass a tailpipe sniffer test you will need a real cat.

 

i dont have to pass the sniffer test just obd2 plug in but its reading bank one and thats the oxygen sensor before the cat. why would that read that the cat is insuffecient

 

I think on a Civic bank 1, sensor 1 is the first one and bank 1, sensor 2 is the second one. Cars with V6 or V8 engines can have two banks, for the pipes and potentially converters are separate for each side of the engine. "Low catalyst efficiency" is definitely a result of the second sensor not reading as expected, because there is no cat.

 

^^^ Makes sense to me. As I understand it, the primary O2 Sensor (before the cat) is the biggest step in adjusting the air/fuel ratio. Between a proper mix and a real cat, the secondary O2 sensor is just a final tweak for emissions. Even if your primary O2 sensor is working right, if you have no cat the secondary O2 sensor will be getting readings that are outside of what its expecting, and will throw a code.

(of course I could be wrong, but that's how it was explained to me and makes a lot of sense)

 

i had the same problem and got myself a blox cel elminator for $15 and that fixed it... no cel for 2000km... so far so good.... if u wanna even cheaper, u can get spark plug non fouler and diy ur own... i am actually using the spark plug non fouler method cause the blox one was too long... my shift linkage hits it every time i shift... for diy method go google and search for "spark plug non fouler o2 sensor"

 

A high flow catalytic converter is called such because it has a catalyst in it that converts the exhaust gases into more environmentally friendly molecules than without a catalyst. A test pipe does not have a catalyst inside of it.

"test pipe high flow cat" is an oxymoron. People on eBay tend to label their items this way in order to keyword spam, and also to potentially trick buyers into thinking they are actually getting a "high flow cat".


ImportTuner did a test (using a dyno) on the same car as yours to test the benefits of a test pipe vs. a real high flow catalytic converter. The benefit of a test pipe vs. the catalytic converter was a measly 1 HP difference, which is outweighed by the consequences.

Driving without a catalytic converter is way worse for the environment than with. It is illegal in all 50 states and many other countries and if a police officer or anyone else with authority catches you, you will be fined. It is bad for other peoples' health, and it is bad for your own health.


I highly suggest you do the right thing and put a catalytic converter back on. Your future grandchildren will thank you.