Help with P0421, P0431 codes, '02 milly s
 

Hello,
Looking for some help.
My '02 millenia-s w/ 100K miles runs great. Smooth, good power, good mileage (23-24). I'm throwing P0421 frequently, P0431 less often. Upstream O2 sensors were recently replaced.
All of the tests are complete except the evap. I've been waiting seemingly forever for that test to finish, just in case it's the downstream O2 sensors or something else that are the problem. Can anyone tell me how I can get the evap test to finish?
The only other things worth noting: I get a little roughness in the engine between 50-60 mph on a flat or slight downgrade; I get blue smoke on startup occasionally; I sometimes smell gasoline fumes.
Basically, I'm trying to determine if it's the precats, the downstream O2s, or something else.
All advice welcome!
Thanks,
Paul

Car Owners: How to be Test-Ready

If your vehicle was recently repaired, or if the battery was disconnected, the information in your vehicle’s built-in computer might not be readable, and the test might not be completed. As a result, you’ll have to re-take the test and you could be delayed in getting your licence sticker.
A day or two of normal highway and city driving will usually reset your vehicle’s computer and ensure it’s ready for the Drive Clean test.
You can also take your vehicle through a “generic drive cycle”:
Step 1: Make sure the vehicle has been parked for eight hours without a start.
Step 2: Start the engine and let it idle in Drive for two-and-a-half minutes with the Air Conditioning (A/C) and rear defroster on.
Step 3: Turn the A/C and rear defroster off. Drive the vehicle for 10 minutes at highway speeds.
Step 4: Drive the vehicle for 20 minutes in stop-and-go traffic.
Step 5: Your drive cycle is complete. You can now go in for your test.

Gas tank should be ¼ to ¾ full. Driver should avoid rapid acceleration.


Another good prep for the test is to put some lacquer thinner in your gas tank about 1 month in advance of the test as this will help clean things (catalytic converter, O2 sensors). Up to 1 gallon of lacquer thinner per 1/2 tank of gas as per video:

Do this, I've done it, it does a good job of cleaning:

those are cat efficiency codes, controlled by the post cat sensors. with the mileage on your car, and the blue smoke, i would say the cats are dying. and, anyone who has changed the cats on a 2.3 would laugh at that video, as i am. you can get the front bank cat off from up top, and use jackstands because you have to pull the Y pipe. be real careful with the nuts and bolts, they are all high nickel alloy, and NON magnetic. you can get precats off ebay, there is a canadian company that sells them cheap. however, i did buy a Y pipe from them, and it did NOT fit. a genuine precat is gonna be expensive. the labor is a killer, too. the rear bank cat is a real bear to get to. i would not even think about it unless i have a lift. the entire exhaust system has to come off to get it out. i know it sounds ridiculous, but you will see. it is like a giant puzzle, to get this off, you gotta pull that, but to get that off, you gotta pull this, and so on. the last one i did took me about 4 hours, but i had a lift, and all of it was done from underneath, except the oxygen sensor. and it was a trick to get it out, too. if you dont care about the car, google spark plug anti foulers. however, the precat "brick" is not a honeycomb, it is like a tightly wound spiral, and it will clog easily. if you are smelling gas, and it is internal, the cats will soon be clogged, if not already. then there can be serious engine damage from back pressure

I AGREE, hence put in lacquer thinner for now and hope code goes away, but it won't solve the problem with oil, but it may post pone the inevitable!

Magnaflow sells pre-cats with exhaust manifolds.
READ: https://www.mazdaforum.com/forum/maz...3-0-ltr-30510/
They are available for other models.

Hi,
I'm going to try the thinner first, while I wait for the evap tests to finish. I had seen that video before too, but hadn't tried it yet.

The Magnaflow precats run in the $500+ range - the ones sold by the Canadian company that Keninn noted go for $229. I hope I don't need one at all, but if I do, I'll probably go the cheap route.

I'm going to also try some stopleak, and I've heard there are specially-formulated oils designed for older cars that can help slow oil leakage. I'll try that too if I can find it.

I'll check back in when I have more to report.
Thanks,

-Paul

I've tried it @ 1/2 strength with no ill effects, only good results. I believe tanprotege has also done it and he a code, don't know what strength he used, but it was very helpful cleaning out the exhaust, O2 sensors.

google atp-205. smoke may be from valve stem seals, dunno if the 205 will work for that, but it is worth a try. i also like valvoline hi mileage oil, i use full synthetic, but they have regular hi mileage oil. this will help. look for the 5 qt jugs in walmart, only some of the stores carry it. and do check your pcv valve. i dont use any stop leak additive, i stick with the hi mileage engine oils. but that dont mean the additives dont work, i just dont use them.

What do you mean by half strength? Half of what Scotty Kilmer recommends? I was going to try 1 Gal. thinner in about a 1/2 tank of gas.

I used 2 liters in 1/2 tank, and drove 45 minutes on the highway.

this says it dont work