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Failed Smog.....uuggg


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Hello Guys, first time posting here for me. But I have used this site on numerous occassions to help resolve issues with my 94 LS400.

So here is the deal. And yes, I have read MANY posts on this, but still am asking for some updated answers, because most of the related information is very old.

CA car.

She failed MISERABLY the first time with double or triple the passing amounts in HC and NOx. After new CAT she barely passed the NOx portion, but still failed the HC portion with about 10% higher readings than allowed. Can anyone show me the location of the EGR Vacuum Modulator and such? Also, could this be O2 sensor related? The new CAT cleaned up a LOT, but clearly there is still some underlying problem, and I really dont want to replace both of the header CATs as they are quite expensive..... thank you.

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The actual numbers:


15MPH 1496 12.80 2.60 56 10 121 0.32 0.00 0.05 477 92 1320 FAIL

25MPH 1434 12.94 2.41 32 7 112 0.30 0.01 0.05 481 100 1702 Gross Polluter

After new CAT:

15MPH 1493 11.59 4.33 56 10 68 0.32 0.00 0.01 477 92 456 FAIL

25MPH 1469 11.60 4.31 32 7 65 0.30 0.01 0.01 481 100 449 FAIL

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Thank you. I removed/cleaned the EGR, but it "appeared" to be operating normally. But I was 'told' the EGR Vacuum Modulator is most common to fail. I have no experience to back this up however....I tested both of the 'pre-cat' O2 sensors, and they appeared to work normally, at least using the voltmeter/propane torch method. But again, I was also told by the smog mechanic that it actually takes an expensive machine to test the O2 sensors due to the rate at which the sensor must perform at. Basically it boils down to how FAST can the sensor process information. I did not check the 'post cat' O2 sensors. I was 'assuming' (and this is where the issue usually begins) that if I had a failed component like EGR or O2 sensor, that I would get a check engine light. But none have showed up. I do have a brake light on, caused by not replacing the brakes with the factory sensor types, and also an Air Bag light which I have no clue what caused that light to come on. I read on another post on how to use a paper clip and jump two terminals to try and diagnose a code issue, but I dont recall the details and cant remember which post it was because of all the posts I have read. So if anybody knows, im willing to listen.....She has new plugs. I checked all the Ohms resistance in all of the wires and they all tested under the maximum....the air cleaner is CLEAN, but not NEW.....Anything else to look for? If I could adjust the ignition timing I would, but its all computer controlled. I just had my Turbo Porsche pass after failing with high NOx and all I did was !Removed! the timing and enrichen the A/F ration via the computer, but I cant seem to do that with the LS. Thanx for any help guys.

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Welcome, Greg.

Just a couple of thoughts... having higher than normal emissions could point to incomplete combustion of the fuel. And usually due to a rich fuel/air mixture.

The fact that you changed the cats and got an improvement suggests to me that your mixture is rich and probably was overwhelming the old, worn cats. They might not have been shot but not working like when they were young pups. The cats basically burn up any remaining fuel in order to lower emissions. You can also tell quite a lot by checking your MPGs. On the highway and driving at 65, you should be getting north of 25 MPG. If it is anything less, then the mixture is probably too rich. I do not know if you have been keeping tabs on your MPG.

So, what makes an engine run rich? Lots of things could. On the older LS, the coolant sensor can get lazy and report a cold engine when it is really up to temp. This causes the computer to enrich the fuel mixture all of the time. Then again, it could truly be a 'cold' engine, the thermostat not keeping the engine up to peak operating temp.

Could also be weak spark because of weak coil(s). I suppose a drastic difference in emissions readings between the two banks(left/right) would point to the offending side. But if they are relatively close, I would declare the coils good.

Just some things to think about. I believe that if I were you, I would swap out the coolant sensor as a start. BTW, here is the lexls site for reading codes -> http://www.lexls.com/tutorials/intro/codereading.html

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Thanx guys. I have the following error codes as my 'check engine' light JUST came on a few days ago while someone ELSE was driving my Lexus... go figure. at any rate, engine codes 25 (lean A/F mix) and the dredded 71 EGR code. I did however clean my EGR valve just a week prior, so maybe by removing the EGR it triggers the code, I dunno. I also have Air Bag code 22 (air bag light indicator) and granted, there is an airbag light on the dash, has been since I bought the car, but I dont know how to correct it. Does anyone know how to reset the airbag codes? I already reset the engine codes and will drive her around for a while to see if the check engine light STAYS off...but who knows. I did not have any O2 sensor codes, so I guess it would be a complete waste of time and money to purchase new O2 Sensors in hopes it would correct my smog issue.....thanx guys/gals

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Ok...so here is what I found out checking the EGR. The OHMS check turned out ok. While still installed on the vehicle, I followed the procedure of disconnecting the battery then checking the resistance between the B1/B2 terminals and all of the S terminals. They were all within 22-23 ohms.. so basically w/in spec. And i was going to leave it at that, but I wanted to make sure, so I removed the EGR valve and checked the plunger/valve opening and closing according to the standard test, which is to apply positive voltage to both of the B terminals, then applying negative/ground to the S terminals in sequence. Basically you ground the S4/S3 terminals, then S3/S2, and so on.... and each time the valve is suppose to open further and further.... now while holding the EGR, I could FEEL the 'clicking' or whatever you wanna call it whenever I would apply negative to the S terminals, but I could not visibly SEE the plunger moving upward, as it should to open the valve. So, I removed the plunger/solenoid from the metal housing and checked further...and sure enough, even though you can FEEL the motor trying to move the plunger, it would not move in either direction when grounding any of the S terminals in sequence. now you can manually move the plunger up/down and it will return to the down position on its own, but the electronic solenoid would not move the plunger up at all...so I am going to ASSUME this means the EGR valve is bad....any thoughts?

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If the plunger is removeable, the core may be dirty and not allowing the movement in the solenoid. I used to work in the electronics field, and a solenoid would become gummed up with debris. However sometimes the coil weakons, and replacement is the only option. Hope this helps.

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