My stock 93 SC300 is not passing the emissions test for NOx gas. I have been researching this for 5 months now and have found that NOx are formed by high combustion chamber gas temps. This can be caused by carbon build-up in the chamber or valves. A plugged EGR can also cause high NOx.

1st test gave 1316 ppm with new wires and plugs, cap, rotor, PCV, O2 sens and air filter.

2nd test gave 1191 after putting seafoam into the intake and in the tank to clean the valves and fuel path.

3rd test gave 1071 after more seafoam treatment and another brand of injector cleaner.

4th test gave 1047 after replacing the EGR with a new one and cleaning the intake passages.

I was stunned this week when it failed again after the new EGR was just installed because I thought for sure that was the problem. I have done all the work myself so I know everything is done correctly. With 175k on the odo, the car has all of the original exhaust that was installed in Japan. From what I understand tho, the cat should not make a difference in NOx emissions. 2 years ago it failed NOx and then passed after I put Seafoam only in the tank.

My next plan is to:
1. Dump alot more seafoam in the intake and tank.
if that doesn't work,
2. Replace the cat,
or
3. Pull the head and do a valve job.
or
4. Find a 1jz-gte

Let me know if I'm overlooking something cuz I'm baffled that it's so hard to get this thing to pass the sniff test. I've always kept it in tune and only run quality fuel.

 

After you seafoam the intake, change your oil as the acids that blow-by the rings from the carbon buildup emulsification will cause breakdown of your oil. Seafoam in the gas is good as well.

Try running the REALLY hard to get the cats REALLY hot before you take it in to get sniffed. This increases the efficiency of the catalyst.

Another way to reduce the combustion temperature is to put really high octane gas in there. After the seafoam, you can try to find a sunoco station that sells 106 octane and put that in there to see if that helps.

 

Move to Louisiana, Run no EGR/Cats, and brag to the local cops/inspection stations about it. Problem fixed

 

Damn coonasses , my wife is from Walker, LA.

 

buy some pure acetone from advance in the paint section. mix 3oz. for every ten gallons. if you really want to pass i guess you can add more. not only does it reduce emissions but gives better gas mileage. also use highest octane gas and do a tune-uplugs,wires,dist. cap, rotor, ignition coil, air filter(BFI). p.s try putting the seafoam in a cup and suck it up through the vacuum hose on the brake booster(do it slow so you dont stall it).

 

If you want to pay you need to add more. 4 gallons of premium gas and 1 gallon acetone = instant pass. Hell cars with no cats have passed smog tests like that. BTW idk how that would work on a turbo car but on na its perfectly safe.

 

hows your timing? and has the engine been rebuilt?

 

high NOx numbers = car is running lean. Have you checked for vac leaks, bad IAC, bad MAF, etc.?

 

After my 1jz I got a reading of 2940.

I win.

 

Check your timing, NOx's are also caused by advanced timing. Is timing part of your inspection? If it isnt I would dump the timimg down to 5 degrees BTDC. That will help a lot. Here in Cali timing its part of the FUNCTIONAL test, your allowed-give or take 2 degrees. Our specs for timing is 10 degrees.

Catalytic converter can also be a culprit but I would replace that last if everything else checks out fine. A 3-way catalytic converter will reduce HydroCarbons/Carbon Monoxides and NOx's.

A 1JZ swap will not help you pass a Smog inspection. It will definetley fail for NOX due to no EGR system and it has a Distribuless ignition system so you will not be able to play with the timing. It may also fail for a VISUAL inspection for not having the right engine size.

 

I forgot to mention check the EGR Vacuum Module, this controls the vacuum going to the EGR. Whenever a Toyota/Lexus fails(mostley Toyotas) for NOx's at out shop then goes out for repairs, most of the time its a bad Vacuum Module.

 

super heating cat wont work unless you do it right before the smog. its against smog rules to super heat it, but if you have a friend doing a smog im sure he can heat it up for you

 

Thanks eyeSOAR
I have not changed the timing, but I will check it now to see what it is. Easy to adjust with the distributor mount. The vacuum module was removed and cleaned with a new foam filter. Vacuum lines all seem fine with no cracks or brittle areas.

Thanks todog and Ryeno
I'll try the fuel additives too. I use the PCV hose to (gradually) suck in the seafoam from a small glass and clear hose so I can see the level drop that way. The PCV line distributes the seafoam across all cylinders better than the brake booster, so I use that with good results.

And change the oil soon after as mentioned.

I will keep you posted and we can all soon breathe easy.

 

I checked the timing and it was at 10deg BTDC as it should be. I adjusted it to 7deg BTDC to reduce the NOx for the next emissions test.

Should I try to retard it more? How far is too far, 0?

Last NOx reading was 1047ppm and I need to get it down to 773 or less to pass.

 

Like i said if you want to pass get 4 gallons of premium gas (you should be using premium anyways) and add 1 gallon of acetone from home depot. Just make sure you check the label and its pure acetone (no water). I am not talking about adding it into the pcv value but into the actual gas tank, BIG DIFFERENCE.

It'll dilute your gasoline so the mpg will drop but will burn a lot cleaner. Here is my smog results with the acetone.