Rex Ruthor

Thinking about installing test pipes to enhance stock exhaust flow while maintaining near stock appearances. My car is a 1994, thus OBD I. Just wondering if the sub-O2 sensors after the cats just sense heating in the ECM like most OBD I vs. OBD II cars. If so, then test pipes could be installed without triggering a MIL. However, Lexus was kind of advanced for its time in the 90's, so I was wondering if the post cat O2 sensors sniff for change in oxygen content from the pre-cat O2 sensors. Also, if so, then would a simple mechanical fix taking the sensors out of the mainstream a little suffice? TIA for anyone who knows.

benz420

running test pipes most likely would set a CEL, for codes 27 and 29 (sub oxygen sensors, left and right banks). they function in much the same way as the main o2 sensors, like you mentioned.

also, you can find and o2 simulator/defouler to help eliminate the CEL, which like you also mentioned, removes the o2 sensor out of the exhaust stream.

Rex Ruthor

Thanks for the input.

JBrewster

You may want to consider a high flow cat. That for sure won't throw a code. Will be a bit more expensive though, but you'll be saving the environment lol...

GSteg

iTrader: (15)

You need to find out what kind of cat you have. Most lexus comes with an already high-flowing cat so you're not going to increase anything except noise and pollution.

Rex Ruthor

Good point. I want to hear that wonderfully designed 4.0 L a bit more. Perhaps custom muffler replacement out back is the best option.

GSteg

iTrader: (15)

The weakest link in the exhaust setup is the header. One quick look and you'll see why they are hindering your performance. I dont have an LS400, but the 4.0 V8 gained about 15whp and 20ftlbs almost throughout the revband on the GS400 and SC430. Gobs of midrange torque available. Of course, they dont come cheap and it (S&S headers) might not fit the first gen LS400.

LiCelsior

iTrader: (32)

they fit Steg, i think its like 700-800 bucks though lol.

GSteg

iTrader: (15)

Do you know anyone who has it on their 1st gen LS400? I'm interested to see how much effect the headers have on the non-VVTi engines.

LiCelsior

iTrader: (32)

only person that i think have done it is prolly Jbrady, he seems like the exhaust god in the LS forum lol. i correct myself, its 600 from Carson.

GSteg

iTrader: (15)

Jbrady has a 2nd gen LS. Practically the same setup as us GS4 guys.

Perhaps someone here should be a guinea pig for the 90-94 L

LiCelsior

iTrader: (32)

i may do the header upgrade if i ultimately decide to keep my 1st gen. i have a exhaust leak on the passenger side header. but my car needs a lot of work (majority paint) and debating if i should upgrade to a 2LS.