Doozy, P0420, 02 Toyota Tacoma. Fixed, but weird.

[Big_P]

This goes out to all the techs out there who get some cars with weird problems. We had an 02 Tacoma, 2.7L come in the other day for a P0420 code. Catalyst Efficiency Below Threshold, Bank 1. Fair enough! We just changed the cat-back exhaust a week or so earlier so it came apart easy. Put on a new cat and sent it on it's way.

Couple days later the code comes back. Odd, we thought. O2's seem to be switching fine, we warrantied the cat. (NAPA Quality parts).

Again, a few days later. What else can we do? There are no exhaust leaks anywhere. We put new oxygen sensors in.

Another week goes by, aaaand the truck is back. Wow. Now we're all stumped. The only thing we can think of is to change the warm-up converter on the exhaust manifold.

One of the guys pulled the truck into his bay and our newbie tech, unaware of the trouble this truck has been through, said "hey, that thing have a performance exhaust on it?"

No, it was actually one from Autopart International, stock exhaust that we replaced a few weeks earlier. It did sound kinda throaty but I didn't even think of it when I put the exhaust on.

So we ordered a NAPA exhaust. Put it on, much quieter. P0420 went away for good. We saved the old cat and O2 sensors and put those back on too, code still gone. Saved the customer big $$, caused our own headache, but we got it fixed so thats what really matters. The exhaust we got from Autopart Int'l must have not had enough backpressure and was causing the O2's to read funny. Something like that? That's all I could think of.

Weeeeird stuff.

Pete

[Spycker]

Damn Toyotas

[RattFink]

Damn Toyotas

lol I agree

[black86glhs]

I have heard of this before, but never seen it. I believe a larger second cat might have taken care of it. Assuming the last O2 is after the second cat. Of course, everyone wants a smaller cat thinking it will run better. The larger cat would help convert more exhaust even with the lower back pressure.

[Rattlesnake]

I run into those all the time. And after having the 1st comeback I found a fix that can take care of it even without replacing the cat. I buy 2 non-foul spark plug adapters and drill one of them where I can put the 02 sensor in it, and then screw them both together. Take the entire unit (adapter+adapter+02) and screw it in the downstream 02 sensor bung and that code will never come back even like I said before, if you leave the same cat. By moving the downstream 02 out of the direct contact with the exhaust stream, its signal is delayed. Of course I will change the cat because I care about the environment and I can make a profit on the cat. This light will keep coming back if you don't do this trick and use the ~$350 direct fit or universal cats from Napa, Advance or whatever you use. If you use the $800-1200 Toyota cat it will magically disappear! Well with this trick I've been sticking it to the MAN! Another problem that I've encounter is that the generic cats will slow down the upstream 02 enough that you kept getting a code for "slow response B1S1 02". The B1S1 0@ bung is right between the pre and post cat in the direct fit aftermarket units. The slow response is caused by the 02 being after the pre-cat. I just weld a bung before the pre cat and move the sensor upstream of the pre cat and problem fixed.

Here are some pictures so you can have an idea.

http://img73.imageshack.us/img73/2057/img1345cq3.jpg
http://poisnus.com/files/Spark%20Plug%20Non%20Fouler%20Mil%20Elims/mil%20elims%20spark%20plug%20fowlers_files/image011.jpg
http://tychl.txf.com/o2mod/tight-fit.jpg

[black86glhs]

I like that idea. It wouldn't surprise me if there in an internal baffle in the toyota ones that isn't in the aftermarket.

[Aries_Turbo]

i have that non fouler thing on my subaru right now. the cats still work, the car doesnt smell at all. it just doesnt work enough for it to pass calif emissions cause its a 50 state car.

it did not work on my wifes neon though though it may have been some other variables as the 02 volts never came up to reasonable values. they were really low and then the code would come back asap. popped the o2 in the stock location and all was well.

Brian

[Rattlesnake]

You have to make sure you give it enough distance from the flow, some cars would need more or less than others. My records is twelve out of twelve.

[Aries_Turbo]

i tried one and two non foulers on the 98 neon. it was like it was too far away. like when you normally would start the car and go drive with the scanner hooked up the rear o2 voltage would slowly rise like normal. with the non foulers in there, it would never rise up and youd get a code for rear o2 voltage within minutes.

i may tinker around with it more in the future but it doesnt matter to me now.

Brian

[turbovanman²]

Big P, it wasn't the exhaust but the cheap NAPA cat, if you put a decent aftermarket cat or OE cat on, then you can run any cat back exhaust. Putting the stock cat back on is merely masking the crappy cat.

Ronaldo, hmmmmmmmm, I have a Mazda Protege with a weak cat, going to try that, thanks.