Help ! Lol.. I had put on a Magna flow downpipe with a high flow Cat 304 stainless that I've only had on the car for about a year n a half, why would the car fail EMMISSIONS? Is it because of the high flow? What if anything can I do to get it to pass? Or just replace the cat all over again ! I have 5 days to get it done.. This sucks BAD ! Any help would rock.. Thanks a ton.. Michael...

 

Not sure how your emissions checks are done, but in my location pre-96 cars get tested at the tail pipe and 96+ they hook into the computer and scan it.

Even non-high flow cats have had a rep of popping an engine code. Even if you car did not flash the "Check Engine" light, the code may have been triggered in the history. Best thing to do, get the car scanned (the computer holds all kinds of data, like last code tripped this ignition down to a full history of codes since it was last cleared). If the code is a PO420, odds are nothing is "wrong", the PCM just does not like the high flow cat.

Your fixes if you are getting a PO420 are:
- have the PCM re-programmed to delete this code. Can be a bit costly, but if ytou can find someone near you with a HP Tuner or DHP Power Tuner, they code delete it for you (a HP Tuner I think requires credits that you may have to pay the owner to use).
- Look up on the internet about using a Spark Plug Non-fouler to space your O2 sensor OUT of the exhaust stream. When I got my high flow cat, I did not originally plan to have the PCM programmed, so I was prepared to do this trick if it came to that. I've read a LOT of people with just about any make/model car used this trick on high flow cats AND aftermarket stock replacements (I actually know a guy that had to do that on a replacement cat).

Hope this helps!

 

Do you have a CEL?

 

Im gonna fail emissions with an aftermarket high-flow cat too. But the CEL is on. Idk the make of the thing, but I wishe the guy before me didn't mess with he exhaust like he did. I've got like a week to order and install a catback/downpipe.

EDIT: Maniac's post might help.

 

Hello, yes, the CEL is on. It has been on since I put the cat on and new o2. I will try what the guys said, i don't know anyone with a programmer so, I'm gonna try the battery first n go from there to clear the code. I know it cleared the code one other time. Can't remember what it was for....
The code comes up as you stated also, it's the P0420 code. I'm sure nothing is wrong with the car, runs perfect accelerates perfect, matter of fact, since I've put it on the car has run better, more performance, better milage everything. Wisconsin has shut down all of its emmission stations and they are now done at service stations and I think they might "press the issue" because it doesn't say the cat is bad, it says it's not good enough. Something close to that.. When my wife gets home with the car and perwork , I'll post the exact statement of what they said. I'm just real surprised it didn't pass, everything passes now days...lol.. This is BS...LOL.... thanks for all the info so far, I'm gonna try n find a programmer... Wish me luck...lol.. Mjc...

 

The CEL is probably what is causing you to fail emissions then, I don't have emissions in my county

 

Ok so the CEL is the reason why your failed. By the name of the thread it seems like the cat itself caused it to fail. I got mine reprogrammed out using zzp's canned pcm tune. Truthfully, I would have never went knowing I had a CEL on.......

 

Yep, gotta remove that code to pass emissions.

 

In my location (and emissions checks are not state wide in Ohio, it's per county that participates in it), if I have a '96 or newer car with a CEL on, no sense going to emissions check, as it's an instant fail. If your computer has no "readiness" data (such as the codes freshly cleared), they can test it the the way they test pre-96 cars. But once you fail by the computer, you must pass by the computer (tail pipe testing is out of the question).

If you cannot get the PCM re-programmed, the next best thing is look up about the anti-fouler trick. In a nutshell:
- Buy the anti-fouler (made for spark plugs, normally found in the Dorman HELP aisle)
- Take one and bore it out with a big drill bit (it needs to fit the O2 prob in it).
- Remove O2 sensor. Most people I've ready who did this say they have to stack 2 non-foulers together to get the code to go away.
- Get the codes cleared, go re-test (or drive around until the CEL is no longer an active code in the computer, could take a day of driving and multiple stops and starts).

This trick is CHEAP (like less then $10 I think). It's just spacing the rear O2 out of the stream. Google it and you can find people with FAR more detail about it.

 

Whats emissions testing? :p but yeah its 5.99 for the plug foulers at autozone i only used one to get my light to go out