stateref

Do LS400s have the same catalytic converters as the sc400? If not does any other Lexus work?

Looking for the third cat (ca car) but only can find ones off of ls400s.

KahnBB6

iTrader: (5)

SC400's and LS400's only have two catalytic convertors IF THEY ARE FEDERAL 49-State Emission models: one on either side of the engine. The rest of the exhaust system is just piping, resonators and the two rear mufflers.

Edit Correction: As both RudysSC and Boergy point out below, I was wrong and mistakenly only looked at SC400 Federal Emission parts diagrams. Apologies OP! CA Emission SC400's DO have a 3rd catalytic convertor. Federal SC400's only have a resonator in that same location.

SC300's have only two catalytic convertors: One primary bolting to the two cast iron in-line exhaust headers and a second that is under the footwell/seat area of the chassis.

The SC400 Federal Emission exhaust system:




The pre-1998 LS400 Federal Emission exhaust system:




The angles of the flanges and the pipe layouts and lengths are different but the number of cats is the same on both V8 cars.

...

Are you perhaps referencing the number of O2 sensors that California vs Federal SC400's have?

All SC300's with CA Emissions all have a 3rd O2 sensor under the car on their secondary cat and all SC300's with OBD2 Federal Emissions from mode year 1996-2000 have the same number of O2 sensors.

I'm not as familiar with CA Emission SC400's but it would not surprise me if those models also have at least a 3rd O2 sensor after the two main cats in the center pipe. Lexus did this to monitor the efficiency of the cats for CA Emissions and all OBD2 vehicles.

.....

The primary OEM cats on SC400 Federal Emission models carry two part numbers: one for the left and one for the right.

The primary OEM cats on LS400 Federal Emission models carry one part number for both left and right.

Tallyhoe

I don't think its a required cat. I have a 93 SC400 Ca car. Those can be removed and replaced by simple piping... Only cats that matter are the 2 front ones. Pic for reference. There may be some O2 sensors back there, but don't throw codes, if I remember correctly

KahnBB6

iTrader: (5)

In California if your car originally came with a certain number of cats you HAVE to have that same number of cats (in the correct OEM or aftermarket CARB E.O. part numbers) on the car.

But SC400's don't have more than two catalytic convertors. SC300's also only have two catalytic convertors. The piping directly under the seating area of an SC400 is not a catalytic convertor but a muffler/resonator built into the OEM exhaust pipe ON Federal SC400's.

In an SC300 the pipe directly under the seating area of the car *IS* the 2nd catalytic convertor. Not applicable to your car, OP.

I am not sure if SC400's have one or more O2 sensors after each catalytic convertor but I would not be surprised if this were the case for CA Emission SC400's. As far as any post-cat O2 sensors being able to throw codes on CA Emission SC400's and OBD2 SC400's... I'll bet they can. Reason: if they are like the 3rd O2 sensor on the #2 cat in CA Emission and OBD2 SC300's they will be four-wire heated O2 sensors which the ECU uses to check for "efficiency" of the catalytic convertor(s). Any post-cat or 2nd downstream cat O2 sensor in these cars doesn't have any bearing on the engine's state of tune but they can and will trigger a code if the O2 readings from them are not what the ECU wants to see (suggesting either of the catalytic convertors are not functioning as they should be).

The unique aspects of the CA Emission SC's vs Federal SC's became less obvious once 1996+ OBD2 model year cars were introduced since all OBD2 emissions monitors incorporated most of the extra engine monitoring sensors those earlier CA Emission cars came with.

Boergy

iTrader: (2)

i have a 97 Sc400 California version with 3 cats. but the 3rd cat is not controlled with a O2 Sensor. The other states have insteed this cat a resonator.

RudysSC

My white '96 SC4 also had that third cat in place... It was quickly cut out and removed along with the rear resonators lol. Passed emissions flawlessly here in CO, however, I'm sure Craig has a valid point that you'd be busted pretty quick at SMOG in CA.

KahnBB6

iTrader: (5)

WOW! Amending my earlier post-- thank you Tom and Rudy for pointing that out! I am not sure why Partsouq doesn't include the correct diagrams for CA models but clearly your cars came with three cats.

Interesting that those cars are not set up with a post-cat O2 sensor on the 3rd catalytic convertor for ECU monitoring the way CA Emission SC300's are designed.

The OP stateref absolutely would be busted in a CA emissions test or BAR inspection if this third catalytic convertor were to be missing. The smog tech would know to look for it based on the under hood emissions labels and by typing the car's VIN into the smog computer. They do sometimes check under cars there for cats with a small mirror to verify all the required cats are in place.

Any car 2001 and older has to go onto an older BAR97 roller dyno system for testing complete with a gas analyzer probe in the tailpipe. 2002 and newer cars can just plug into the smog computer through the OBD2 port. California ARB doesn't consider 1996-2001 OBD2 monitoring to be advanced enough to make the cut so even those early OBD2 model years get tested almost the same as OBD1 cars.

As far as the 3rd cat goes... even with no O2 sensor on it I am sure it is there in order to reduce overall emissions per the CA allowed CO HC and NOx numbers.

It could be worse though. If I recall, for the 1986+ Fox Body Mustang CA Emission 5.0L V8 models which went to fuel injection there were FOUR catalytic convertors from the factory.

I can certainly see, in theory, the LS400 CA Emission model of the same model year as the OP's SC400 probably using the same basic OEM cat part but welded into different piping.

It's the same engine, same horsepower and torque, same transmission and similar ECU programming with the only major driveline differences being the final drive ratios (3.615:1 for the LS400 pre-98 and 3.916:1 for the SC400 pre-98) and the weight of each chassis... so it stands to reason that both cars would have pretty much the same emissions hardware for the same sales market.

Aftermarket exhaust shops have a lot of restrictions on which aftermarket cats are approved in which locations to install in cars that have worn out their OEM cat(s).

RudysSC

I'm not sure why that would be Craig! I have no idea what part of the country my '96 was from originally so I can't comment on if it was a CA car or not. But, man, talking about it sure makes me miss it!

KahnBB6

iTrader: (5)

I sympathize, Rudy! Special cars that come into and leave our lives are never forgotten!

RudysSC

Craig - aint that the truth! With the third cat delete, no resonators, and borla axle backs that car sounded absolutely stunning. If you're thoughtful about a 1UZ exhaust they can sound so exotic compared to your run of the mill V8 with straight pipes.

t2d2

iTrader: (8)

My neighbors with their M3's and M5's, and my old neighbor with his collection of C4 Corvettes, always rave about my SC's exhaust note.

pishta

F'n with these '92 CAL spec cats: 3 total. 2 off the manifolds and 1 as the 2-1 union. The cats off the manifolds have pre and post O2 sensors and mine are wrecked as I lost a coil and kid ran it for 5 minutes before shutting it down and calling me. all that unburned gas burned in the 2 cats and broke up the honeycomb. Car sounds like a rattlesnake on acceleration. So I need 2 new CARB spec cats and Im down there trying to figure out how I'm going to get a socket on the 3 nuts of the top flange. I get a clear shot of 1 with a 12" extension and have top use a 24" piece of pipe on the 1/2 drive ratchet as a breaker bar (my BB was too long) and then had to JACK UP THE PIPE END with a floor jack to break that F'n 14mm nut. holy hell, that was on tight, I got no chance getting the other 2 off as the shape of the convertor overhangs the nuts for a deep well socket and one I cant even get an extension between the cat and some support that Ill probably have to take off. I can get a box end on either but there is no swing room and I wont be able to break them anyway. Im not sure of the state of the 3rd convertor but out of 56 max HC, I blew a 129, then a 99 and after I fixed a vacuum leak and a bottle of "emissions pass" and 2 more tanks of premium, I blew a 156! WTF> Guy said the cats are probably wasted and I tend to agree. My NOx went down from 530 to 74 to 36(!!) by only using premium fuel for the test, who knew crappy E10 cal sludge gas was so bad in these cars for NOx. Well, WE know now. Saw a vid on comparing FED cats to CARB cats and it was really amazing that the CARB cats were SO much more efficient , like 100 times better in HC and NOx reduction. No wonder they are 4X the price. So Im seriously thinking about selling this car as is for a drift car or no smog state sale. Car runs great complete stock, bad paint. daily driver. So. Cal