My 1993 Ls400 Failed Emissions, Help Please!

[DAZZX]

HIGH MY 1993 LS400 FAILED EMISSIONS TWICE. HC-PPM FAILED NOX PPM FAILED. BOTH FAILED THE 25/25 TEST BOTH TIMES. HERE ARE MY READINGS SO YOU GUYS CAN HELP ME.

FIRST TEST

25/25

ALLOWED

HC-PPM 126/103

CO .23/57

NOX PPM 808/712

CO+CO2 14.3

SECOND TEST

25/25

ALLOWED

HC-PPM 121/103

CO .24/57

NOX PPM 858/712

CO+CO2 14.6

BEFORE THE SECOND TEST, I REMOVED AND CLEANED THE PLENUM, THROTTLE VALVE AND EGR VALVE OF CARBON. THEN LATER AFTER REASSEMBLY I SEAFOAMED IT TO DEATH.OK WHEN I PUT MY HANDS WITH GLOVES ON OVER THE TAILPIPES THE ENGINE DIDN'T STUMBLE ,PLUS IT WAS SUCKING IN MY GLOVES.I HAVE NO CHECK ENGINE LIGHT. NO CODES ON THE DASH. WHEN I FIRST ACCELERATE TO 1000 TO 1500 RPM AT TAKE OFF, I NEARLY HAVE TO PUSH THE GAS PEDDLE HALF WAY IN. DO I HAVE BAD CATS OR O2 SENSORS? AM I RUNNING RICH OR LEAN. PLEASE HELP IT'S MY WORK CAR!!!

IT HAS 32O K MILES ON IT. BOY I HATE GEORGIA EMISSIONS

DAZZX

[DAZZX]

OK I MIGHT BE RUNNING LEAN

[TA in KC]

OK I MIGHT BE RUNNING LEAN

From what other people have said it sounds like you might have a catalytic converter problem. Someone else more knowledgeable than myself can probably confirm if that really is the case. Oxygen sensors are cheap enough that you may as well replace them, it could also be them causing the problem if you are running lean. I did both my main ones on my LS400 with universal Denso sensors purchased off eBay. Total cost was about $50 plus 2 hours of my time installing them. Greatly improved my car's performance and fuel economy. And the air-fuel ratio mixture is correct again. Hope you solve your problem. Thomas

[paulo57509]

I'm no emissions expert. That said, I'll take a stab at it.

High NOx indicates high combustion chamber temps. High combustion chamber temps indicate a lean condition or an EGR system that isn't working, plugged, etc. However, the HC reading is also high which would indicate a rich condition or the cat is weak.

I'm not familiar with GA emission tests.....what is a 25/25 test? In CA they test at 15mph and 25mph.

I'm sure that the test was done using a five gas analyser. Please post all the HC, NOx, CO, CO2 and O2 numbers at all the various test conditions, if possible. Usually, you need to look at the entire picture, not just the snap shot when diagnosing emission test results.

Also, did the tech doing the test get the engine good and hot before testing?

I've attached a couple of tech articles regarding emissions, etc.

emissions_analysis.pdf

combustion_chemistry.pdf

[SKperformance]

If everything is way off then yours cats are dead.

[DAZZX]

They don't do o2 test in Georgia. They do a 50/15 test and a 25/25 test. I think that 25/25 means a 25 pound load at 25 mph.Ok the cat on the passenger side is the original. plus all 4 02 sensors are the original. I might be running rich and lean. Is that possible.The high carbon buildup I saw leading down into the intake manifold looked 1 inch thick.I took a flash light and shined down in some of the sparkplug holes.All I could see was black.How could this be helped?

[91LS400vgb]

Wow - if all 4 O2 sensors are original w/ 320k miles, then I would definitely replace them. After I replaced mine (w/ only 100k), my emissions improved and my fuel economy improved considerably.

[DAZZX]

Ok thanks. Thanks to everyone thatr heped me out. i'll let you'll know the results.