Author Topic: Cutting off the CAT ??? (Read 2936 times)

Strongbad · « **on:** July 19, 2006, 10:42:52 AM »

looking for some help.
Recently my 97 TJ 4.0L has been running rough on the highway under full throttle. It bogs, hesitates, and then when you let up it finally accelarates. and the mileage is HORRIFIC. codes pop up of 51 & 52 & 14. About a month ago, I replaced the upstream O2 sensor. Everything was fine, recently the same codes appeared, and after doing some digging, people have reccomended changing the MAP sensor. I did, and the same codes appear. I then changed the downstream O2 sensor, and the same symptoms appear. Now I have heard two things, Jeeps only like OEM O2 sensors. (upstream is aftermarket, and downstream is OEM) or the CAT is plugged?
If its the CAT, I was looking at cutting it out, putting in straight pipe and putting a bolt in the pipe to reconnect the downstream O2 sensor.

So my two questions are this: Will cutting off the CAT, and putting the O2 sensor back in make it run like crap?
AND
has anyone had similar problems, and how did you solve it?

thanks.

Da_chopper · « **Reply #1 on:** July 19, 2006, 12:49:12 PM »

Is that legal?

BlackYJ · « **Reply #2 on:** July 19, 2006, 12:56:52 PM »

Remove the cat is not legal, however it is not enforced so have at it. I removed mine and just put in a resonator about 4 years ago. I know when my cat was toast, power and gas mileage sucked bad. Now can having no cat and a downstream O2 sensor you may run into problems but i am sure someone with a TJ will chime in.

Strongbad · « **Reply #3 on:** July 19, 2006, 01:14:08 PM »

i know its only streching the law on cutting out the cat. But a new cat installed is close to 4bills, so a hundred dollar option is a good way out.
I know the cat isn't there as nessesity, but am curious like you say if any problems will occur. at first the check engine light will come on, but after a hard reset I hope it will go out.

Has anyone ever found a place where you can buy a fake O2 sensor that tricks the computer into thinking the CAT is still there? they are available is the US. but I haven't seen one here.

BlackYJ · « **Reply #4 on:** July 19, 2006, 01:24:46 PM »

I just read somewhere in the last day or so about a simulator or something for the DS O2 sensor, but now I cant find the thread

Abrasive · « **Reply #5 on:** July 19, 2006, 01:44:19 PM »

I had a muffler shop take my CAT out and replace the rear O2 sensor with a simulator. I got them to just put a test pipe in place of the CAT.
Call around to muffler shops and they'll be able to give you a price. I paid about $480 all told, but also had them replace the muffler with a magnaflow unit.

Strongbad · « **Reply #6 on:** July 19, 2006, 01:47:29 PM »

Did you buy the O2 Simulator from a muffler shop ??

We'll find out soon enough how it runs, the beast is at the shop getting the CAT cut off.

DGenR8 · « **Reply #7 on:** July 19, 2006, 02:25:01 PM »

I had Calgary Muffler remove the cat in my TJ and they charged me an extra $20 to put the downstream O2 sensor into the pipe. It was $110 total.
The jeep ran way better after getting this done and no trtouble codes.

Strongbad · « **Reply #8 on:** July 19, 2006, 02:33:14 PM »

Thats where I'm getting it done right now, and they're putting in the downstream O2 sensor into the pipe too. Hopefully I get lucky like you and don't have any error codes.
Cheers !

HIWYH8R · « **Reply #9 on:** July 19, 2006, 09:01:11 PM »

Depending on the year you slill may have the TWC (three way converter) code. The first O2 sensor fluctuates between .1 and .9 volts as the computer adjusts fuel mixture. The one after the cat stays at a constant voltage because a working cat removes most of the bad stuff coming out.

A bad cat or removing it and just installing the O2 in the pipe is no different then just having the O2 right by the first O2, it sees the same thing and fluctuates and the computer sees this fluctuation as not normal and thinks the cat is bad. Both O2 sensors are basically the same, but the computer does NOT use the after cat O2 for fuel management, so nothing happens to the running engine. It's just used as a monitor to know when the cat goes bad.

Which is why people use those way overpriced simmulators. A simple circut to output a contant voltage and simmulate the heater is all that's needed. Search the web for a homemade one. I haven't but there probably some stuff in the ricer/tunner sites.

Kel

GiS · « **Reply #10 on:** July 20, 2006, 07:35:55 AM »

Have had no cat, and no downstream O2 for 3 yrs now... :shock:

Strongbad · « **Reply #11 on:** July 20, 2006, 08:05:59 AM »

So, $100 bucks later and it so far is running fine.
No engine codes have come up, only time will tell if the same symptoms appear when accelerating past 120, and if the mileage will stay constant when on the highway.

thanks for the help.

HIWYH8R · « **Reply #12 on:** July 20, 2006, 09:25:31 PM »

Like I said, depends on the year and computer coding they used.

redbull · « **Reply #13 on:** July 20, 2006, 09:52:33 PM »

Quote from: "Strongbad"

So, $100 bucks later and it so far is running fine.

How's the sound change? My cat collapsed and I decided to replace it with a resonator to keep the sound a little quieter.

Strongbad · « **Reply #14 on:** July 21, 2006, 08:21:59 AM »

The sound difference is minimal. A little throatier, but its not like you put on a flowmaster series II or anything. So far so good.

Author Topic: Cutting off the CAT ??? (Read 2936 times)

Da_chopper

Abrasive

HIWYH8R

HIWYH8R