Possibly putting a Cat back on

[AlexTJ]

Since I'm making plenty of money through summer I'm thinking of completely re-doing my exhaust setup but there are a few mods the money may be better spent on for now. I currently so not have a cat on, the old one shattered and clogged my muffler to hell. I was in high school at the time making minimum wage so I cut the muffler and cat off and put on a pipe and a glasspack. Now I run just a flowmaster super 44 with a turndown right after the transfer case. All of it is 2.25" pipe.

If I do get a cat, is there a alternative to the expensive random techs that still flow better than stock?

Here's how I see the argument of getting a new Cat:

Pro: Legal
The environment is happier (less guilt)
2.5" piping
OBDII Jeep gets to run in closed loop.
My heater may function again.
Jeep will smell a bit nicer.

Con: Yes, its bad for the environment, I feel guilty, but Kansas doesn't have smog checks so I'm alright for now
My stroker currently runs very cool, always at thermostat temp even in 100 degrees.
The money could go to much needed steering/suspension fixes.
I could get/build a sim to put it back into closed loop

My honest question is, will the stroker with a stock OBDII computer run better if I put one back on? I am concerned since its in open loop all the time it may be running rich with 24# injectors. Also I bet I'll get better millage with one as long as its not too restrictive right?

What do you guys run/recommend?

[shawnxj]

all a cat does is burn your unused fuel. something else is wrong if it's running in open loop and your heater won't work.

if your heaters not working then your heater core is mostly clogged. 1 possible fix for that is to take the hoses off the engine that runs to the heater core and flush it with a washer hose. it'll either clear the blockage or it'll cause the core to leak which will then need replacement. i've had good luck with being able to unclog mine on a couple vehicles this way

if the jeeps not running in closed loop do you have an o2 sensor the computer can read on it? widebands are great to see what's happening but stock computers can't read them

[AlexTJ]

all a cat does is burn your unused fuel. something else is wrong if it's running in open loop and your heater won't work.

if your heaters not working then your heater core is mostly clogged. 1 possible fix for that is to take the hoses off the engine that runs to the heater core and flush it with a washer hose. it'll either clear the blockage or it'll cause the core to leak which will then need replacement. i've had good luck with being able to unclog mine on a couple vehicles this way

if the jeeps not running in closed loop do you have an o2 sensor the computer can read on it? widebands are great to see what's happening but stock computers can't read them

The heater works ( even had the core checked at a radiator shop a couple years back) its just that the Jeep takes forever to warm up since it can release heat much easier with out all the back pressure created by the cat. Once it does warm up the coolant will never go above 195deg as opposed to the usual 210. With that 15 deg difference the heater just doesn't seem to work as well.

Its got the pre-cat O2 sensor, just not the second sensor which checks on the cat. I"m pretty sure if it cant detect that the cat is working it will stay in open loop. I also read in my FSM and heard elsewhere that the second 02 controls a little bit of the fuel trim, but that could just be because it has the power to leave the engine in open loop. Any pro's on the Jeep OBDII system out there?

[shawnxj]

i've always been told the rear o2 sensors don't do anything but check on the cat and that they don't have any input for the a/f

kinda weird your heater doesn't get hot enough at 195 degrees. my truck has a 160 degree t stat but the gauge never goes over 140 and i can roast people in my cab if i turn it all the way up

[AlexTJ]

Yeah, but I've had others say it affects a small amount of fuel trim, but even 10% would matter. If it doesn't affect fuel trim directly, leaving the jeep in open loop all the time certainly will.

And I dunno about that heater, all the hoses, the water pump, the thermostat and the thermostat housing have been replaced, some multiple times. It must be an HVAC issue and not a coolant temp one.

[92tank]

on the heater issuse, your heater core fins could be plugged so the air cant pass though properly. i think mine is that way just havent had time to pull the box and clean it. we all know what conditions the jeeps see, so between dirt, moisture and possible dogs (hair).

[AlexTJ]

on the heater issuse, your heater core fins could be plugged so the air cant pass though properly. i think mine is that way just havent had time to pull the box and clean it. we all know what conditions the jeeps see, so between dirt, moisture and possible dogs (hair).

My dog's hair is all over the passenger seat!

[lafrad]

The cat won't let the engine heat up faster. the size and flow of the devices available for I6 (stroker or no) flows well enough to not cause a significant change in heat escape from the engine. if it did, the MPG would be even more horrible than it already is, in a significant way.

the rear O2 sensor being unhappy is a very possible way for the engine to run in Open Loop. I would not want to be running this way on a stroker, as a key element of making these work is allowing the computer to adjust to the changes in the engine (new displacement, cam, injectors, etc etc etc). It SHOULD maintain closed loop even without a catalyst, if you put the rear O2 sensor back in the exhaust flow. if you move it far enough back, you may be able to get it to even be happy with what it sees... if not, it should just throw a "catalyst efficiency" code, and that shouldn't knock it out of open loop.

Open loop operation can easily cause a "slow warmup". too rich or too lean means the engine isn't running as efficiently as it should be.

[BADASYJ]

The CAT is nothing more than a gimmic and another way for the govt to enforce its will upon us. Global Climate change is cyclical it has happened many times throughout earths existance and it IS DOCUMENTED. It IS about control. They grab just a little piece at a time so nobody really notices until its to late. But they sugar coat it and say its for the enviorment and our saftey or for the children. They try to guilt us into complying.
One volcano eruption puts more toxins and pollutants in the air then man has done in its entire existance. So no need to feel bad or guilty about not having a CAT. It will make no difference to this great earth whether you run one or not. But in my opinion it would be better to put the cost of the cat towards something that will make a real difference. The CAT will rob you of power and it will go bad, causing another headache. Also the feds say you cant remove them and must replace them when they go bad, so thats another reason to leave it off. Buck the system.
Just had to do a little venting.

[Muad'Dib]

Im Pre OBD (RENIX) and dont run a cat... although when i upgrade my exhaust system, i am going to get a high flow one .. FWIW.

[AlexTJ]

The cat won't let the engine heat up faster. the size and flow of the devices available for I6 (stroker or no) flows well enough to not cause a significant change in heat escape from the engine. if it did, the MPG would be even more horrible than it already is, in a significant way.

the rear O2 sensor being unhappy is a very possible way for the engine to run in Open Loop. I would not want to be running this way on a stroker, as a key element of making these work is allowing the computer to adjust to the changes in the engine (new displacement, cam, injectors, etc etc etc). It SHOULD maintain closed loop even without a catalyst, if you put the rear O2 sensor back in the exhaust flow. if you move it far enough back, you may be able to get it to even be happy with what it sees... if not, it should just throw a "catalyst efficiency" code, and that shouldn't knock it out of open loop.

Open loop operation can easily cause a "slow warmup". too rich or too lean means the engine isn't running as efficiently as it should be.

So running with the second 02 plugged in, with a welded bung somewhere in the system, is better than not having it plugged in (like it is currently)?

[gradon]

I had a 94 before my 96 and when I swapped over the borla header>magnaflow cat>borla cat-back combo to the 96, I didn't have a bung post-cat and temporarily ran w/ the 2nd o2 unconnected. It ran like doo-doo. Then, I melted a 3-mo old 2-bung magnaflow cat when my pcm was learning the lt1 injectors in the stroker, so I currently have an SS 2-bung "test-pipe" with the innovate wideband o2 in the front hole and stock post-cat o2 in the 2nd hole. It wasn't until 6-8 months ago that I started getting a "high voltage b1s2 o2 CEL" so dunno if it needs replacement or if it really is running rich(high=rich). Once I get the AEM FIC dialed in, I'll spend another $50-70 and buy another cat, cause I do think the obd2 systems run better with one in.

[seanyb505]

While I dont have the fancy tools to fiddle like gradon, my 97 (ODBII). It was making the rattling/knocking noise in 2004 and I was strapped so I had it taken off. I dont know about running better but it definitely did not run worse. I got better mileage without. Seat of the pants felt nice too. Both then 4.0 and the 4.6 had good idles, I never noticed anything that alarmed me. I do feel guilty, and will likely get a universal if I find too much money in my pocket one day.

[SilverXJ]

Sean, you don't get a MIL w/o the cat?

I'm on the guilty feeling side too. I have removed the two precats and simmed out the after cat O2 sensors. While I could remove all cats I prefer to keep the main cat. Although I think it has an exhaust leak and needs to be replaced.

[SilverXJ]

It wasn't until 6-8 months ago that I started getting a "high voltage b1s2 o2 CEL" so dunno if it needs replacement or if it really is running rich(high=rich).

One trick I have heard of is to back the after cat o2 sensor out with one of those spark plug things. Or you could always sim it out. I have caspers and they have been in there with out problems for like 60,000 miles. Unfortunately Casper isn't allowed to make sims anymore, but you can find other ones.