How To Fix Emission Problems To Pass Inspection?

[z_johnq]

Hi,

My 91 LS400 failed inspection today: HC and CO2 are too high. I used to use Bosch plugs but I replaced them a couple of years ago with NGK; newly changed timing belt and water pump (in fact, timing belt was OK; but the bearing on the water pump was gone). After the replacement, the car runs great and there was no misfire, not stalling, no hesitation as accelerating... The only problems that I have are the exhaust smells pretty bad (but not like rotten eggs); the valve clearance needs adjusting because you can hear the clicks as the engine idling.

According to the inspection report, as the engines idles at around 650 rpm, the HC is over 360 (standard is 220); as idling at 2500 rpm, HC is back to normal; but in both situations, CO2 is high. I suspect the valve clearance has something to do with the HC emission. Because at around 2500 rpm, you won't be able to hear the clicks as the engine idles at 650. Not sure if I make sense.

I poured a bottle of 'CRC Guraranty pass' into the gas tank but it did not help. Maybe I did not use up the whole tank of gas before the inspection, as the instruction says, then it did not help.

Thanks in advance.

[steve2006]

Is the servicing up to date?

A clogged air filter along with old oil will increase emmisions.

[billydpowell]

you might want to check your codes also.. your 02 sensors should tell you..

[SRK]

Probably you mean the CO is high, which means a rich mixture. CO2 is the result of perfect combustion, something lost entirely on the "greenies".

For sure check for any O2 sensor codes as Billy mentioned. If they are within spec, particularly the pre cat ones, then the problem is a bad catalytic converter more than likely. For sure it's not a valve clearance issue. Perhaps if one or more was tight enough to produce a misfire, but loose won't do anything.

[z_johnq]

Thanks guys.

I haven't checked it yet but the air filter should be around a year old. Do you think it's bad enough to fail the inspection? But I'll certainly check: thanks for the reminder.

I cannot check the code since the CEL is not on. I used to check it by reading the number of the flashes of the CEL as the CEL was on. I think the code was 28 (not quite sure; flash twice then stop for 3 seconds; then flash 8 times; then the same cycle again until turn it off), which meant the oxy sensor on bank 2 before the cat was faulty. I replaced it but did not help much: CEL came back on after a couple of months...

Do you guys think that faulty oxy sensors can cause the bad smell in exhaust in stead of the cats, and the failure in inspection? I think the cats are more likely to be the culprit. If they can, I did not know they were that powerful.

OK, I'll check the air filters and the code again, even the CEL is not on (it's possible it's already burnt out).

Btw, I got a typo in my first email: it was CO too high, not CO2. If it was CO2, it should be good news. Sorry.

Thanks again.

[z_johnq]

Sorry but I missed SRK's comments. Yea, I agree with you. Check the O2 sensors first, following the specs from the repair manual. I still doubt the bad exhaust would be gone with the replacement of the sensors. SRK is right. It was CO, not CO2. My mistake again.

Thank you all again.

[SRK]

It's not the air filter - the mass air flow sensor compensates for that to a point.

The cat can produce a smell either from an incorrect mixture being sent to it ( bad O2 sensor, engine fault, misfire etc) or because the cat itself is faulty. Which is why I mentioned that if you can confirm the O2's are fine, in the absence of a an actual misfire it could be that one of the cats is bad. You don't mention what the mileage on the car is.

[z_johnq]

I'm sure there is no misfire now. I put my hand at the tail-pipe and I can feel very steady and constant puff-out. A few years ago, before I replaced the Bosch plugs with NGK, I could feel some random misfire. Not any more after the plug replacement and some of the cables.

The mileage is about 166k.

I'll keep you guys posted after I checked the sensors.

Btw, in case I want to replace the cats, do you think the universal ones are OK (those without the flange)? It's about $70 each on Ebay.

Thanks again.

[SRK]

I have no experience with aftermarket cats, and the ones you mention seem very cheap.

One of the strategies used in modern engines is a rich program under full throttle. It serves to protect the engine from overheating, but it also heats up the cats to clean them. If you haven't driven the car hard it might be an idea to do a few full throttle blasts ( up highway on ramps and such) and get the engine working hard. My LS smelled very badly for the first few weeks after I bought it used. A few hard drives and it ran far better and didn't smell. Here in Canada at our temperature we also get a lot of water in the exhaust system - so steam and black sludge come out of the exhaust along with liquid water after driving slowly and then beating on the engine.

It might be all you need to do to improve the cat efficiency.

[billydpowell]

on my old 94, it failed, and codes said cats, I tried every cheap way to cheat it, didnt work, bit the bullet got exact fit new ones and it passed.... so hope you do better with SRK's test, but stay away from welding cats on...

my dad said a hint to the wise is sufficient..

[z_johnq]

Billydpowell,

How would you know the universal cats are no good? I suspect they would be good but planning to try.

I'm not sure if it's worth it to replace with those who have the flanges. At twice as expensive as the universals.

Thanks in advance.

[billydpowell]

Billydpowell,

How would you know the universal cats are no good? I suspect they would be good but planning to try.

I'm not sure if it's worth it to replace with those who have the flanges. At twice as expensive as the universals.

Thanks in advance.

they are not that expensive 126. each http://www.ebay.com/itm/New-Catalytic-Converter-Front-Passenger-Right-or-Driver-Left-Side-RH-LH-Hand-/231029627850?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A1994%7CMake%3ALexus%7CModel%3ALS400&hash=item35ca705bca&vxp=mtr

all I said was stay away from welding cats on.

[z_johnq]

Thanks Billy. I'd try those you recommended if I found out mine are really bad. I've already contacted a few garages but they told me they did not have the equipment for the old models (OBD II won't work on those cars), to check if the sensors and cats are OK. I'll keep trying.

Thanks again.

[Garo_mcc]

Try a bottle of fuel system cleaner and drive the car hard though a tank of fuel. Might just need the Italian tune up!