Catback Exhuast

[lexfourcam]

I want to know if removing the cats off a 94 ls400 will cause it to run poorly. I was told at the dealership that the car is getting a bad signal and the computer is confused. I'm really thinking of buying some new cats because i had to remove the old ones because the exhaust flange didn't match up with the cat.

[curiousB]

I want to know if removing the cats off a 94 ls400 will cause it to run poorly. I was told at the dealership that the car is getting a bad signal and the computer is confused. I'm really thinking of buying some new cats because i had to remove the old ones because the exhaust flange didn't match up with the cat.

????!!???? Its hard to follow what you are asking. Are you asking if you can remove CATs or are you telling us you did already? Are you now seeing performance issues and CEL problems since removing them? I'm also puzzled how an exhaust flange wouldn't line up to a factory installed (i.e. the old ones) CAT that has been there for 16 years....

Maybe you should rewrite your post so we can understand what you are asking.....

[lexfourcam]

well i added headers to the car a while back and the catalytic converters off the 94 didn't match up because the flange on the shorty's was different. I've always had an engine light on since then and performance problems but haven't really had the money to fix it. I finally was able to take it to the dealer and they said because the catalytic converters aren't present the post cat o2 sensors are getting a bad signal and causing the computer to mess up. I read somewhere else that only obdII has a warning light for the o2 sesnsors after the cats, so would this cause my car to throw another code since theres not one stored in the computer to post? the car runs great on a cold start or should i say the gas pedal is very touchy but after it warms up it seems its lost quite a bit of power.

[billydpowell]

ADVICE...

put it back original and your problem is solved,

why do you need headers anyway????

[curiousB]

I agree with Billy. You'll never pass an emissions test doing what you've done. Also at 3,858 lbs this is never going to be a muscle car. The few added horsepower won't even be noticed with such a heavy vehicle. In fact you probably didn't gain any HP because the ECU is confused without proper O2 feedback signals and is making poor fuel/air decisions.

I'd put it back to stock and get the emissions under control and proper performance.

[RDM]

The emissions control system on the 1st generation LS is archaic to put it nicely. If you choose to run without catalytic converters, you must use either a simulator to trick the ECU into thinking they're present, or add spacers and push the rear O2 sensors further out of the exhaust stream to reduce the O2 measurement, thereby letting the ECU know there's at least a small change in value between the primary sensors and secondaries. Both of these though are bandaids to correct the real problem, which is not have the converters installed. They sell numerous flanges online and you can cut your existing flanges off if need be, and there are plenty of weld in converters without flanges that you can adapt to make them work properly. It sounds like you just don't want to spend the money to do that, which is fine, but you're not going to correct the problem any other way.

[lexfourcam]

thanks for the replies, well the gasket in between went bad and to change them they had to do quite a bit of work so i figured i'd give the headers a shot. the flanges are for a newer ls400's cats so i'm thinking if i get cats for a newer ls the flange will match up perfect. Thanks for the trick rdm should i use a washer or a nut to space the o2 sensors? I know the ls400 is no performance vehicle but the engine is legendary and after reading about the 1uzfe on lextreme i was quite interested. Of course exhaust and intake give you the slightest of an improvement they are the most marked up items on the modification market. Also in FL there's no emissions testing but if your car is a little too loud or you lay down on the gas they'll write you a fat ticket for excessive noise...

[killerFatty]

whats your exhaust set up like after the cats? I was thinking about cutting everything off right after the cats and having 2 1/4 inch ran into an X-pipe and then splitting it into 2 borla's to finish it off.

[lexfourcam]

Ordered new cats today! Right now i have two straight pipes which is loud and abnoxious and doesn't supply the motor with enough back pressure so it's lacking in the low end torque area. The x pipe is what i'm getting i'm not getting borlas because i just spent 400 dollars on new cats but i got some cherry bombs in storage and hopefully they'll be alot more quiet than the flo masters.

[lexfourcam]

Well i went and got the cats put on at the local exhaust shop which was more trouble than it was worth.... absolutely no difference at all, no improvement check engine light still comes and goes and it still feels like i'm driving a ls400 with a civic motor. I'm taking it to that shop again for them to do a diagnosis on it. I won't say that was a waste of 600 dollars but at least the car is legal...