donbrew

I even tried an internet search.

I got a P0420 the other day, cleared it. Popped back a few thousand later. I was hoping that it was my flex pipe, since I have a new one in the garage.

I pulled the catalytic converter off. The 2008-2011 LTs actually have 2 on the one pipe. The flex pipe is good.

My observation: The inside of the pipe at the header end is a bit sooty (dry). But, the inside of the pipe after the second cat is oily and has small white particles in it.

So, I am writing off the cat I guess. The question is: What is the oily stuff? Is that the cause of failure? What's the cause of the oily stuff? I do not want to destroy a new cat.

firemangeorge

Maybe it's "cat poop". (Sorry, couldn't resist.)
Actually donbrew, I don't have a clue. I haven't looked inside too many convertors, so that's a new one to me.
I would be interested to know what the answer is. I'm never too old to learn something new.

Oldblue

the last time I saw an oily residue after the cat, it was from a leaking head gasket, the antifreeze clogged the cat , now that was on my 355 Chevy pickup truck but it was Dex-cool 50 50 mix I was running so it my be that, but I can't be positive

donbrew

I did burn some oil between oil changes recently, but I'm puzzled about it being after the cat. I am assuming that the tiny white balls are precious metals?

And now for further confusion: I put it all back together with a new header gasket, All of the codes disappeared including the "permanent" saved one.

Now I am thinking the #2 HO2S is fouled, since the voltage is not very steady and sometimes dips significantly at idle.

Related to this is the fact that I got a "check gas cap" and a purge system code (don't remember the #) that I cleared with no return. HOWEVER, the ECM is still reporting that the "test is not completed", no CEL, no code, just "not ready for emissions test". Where I live I don't need an emissions test (thankfully), but I hate unresolved errors.

db/sb

That will clear after you've driven your HHR for a while. When you clear codes, either by using a code reader or disconnection of the battery, the I/M readiness monitors have to reset.

Lucky

A quick easy test of the cat can be done with a non contact thermometer. Start checking the temp at the manifold and work your way back if the cat is working it will be hundreds of degrees higher than any other part of the exhaust if the temp of the cat is close to the temp of the other exhaust parts then it's not working. This test needs to be done when engine is warm and at idle.

donbrew

I tried that. New information says that newer systems don't make for more than 50F difference, so may not be reliable. My IR thermometer only reads to 1400F or so; the 2 cat configuration makes it difficult. My results: at the header- over temp, at the top cat- over temp, between cats- over temp, second cat- 1400F, after second cat- 126F.

The down stream O2 sensor is between the cats, BTW.

My manifold vacuum tests seem to say no exhaust blockage or vacuum leaks. I.E. drops on acceleration then recovers quickly.
The voltage of the up stream sensors varies wildly, as it should.
The voltage of the downstream sensor varies slightly and sometimes drops significantly. It should be steady. This leads me to think "lazy sensor".
The fuel trim at the up stream varies between within specs, as it should.
The fuel trim at the down stream sits at 92.1.
I couldn't get the dammed PCV hose un hooked to do a "forced rich" test of the down stream O2 sensor.

I have driven 6 days now with the Evap test not completed, over 1500 miles. Even tried to do a "drive cycle" by the book today. I usually start out the day with about 1/2 tank or less, and my drive to the gas station gets close to a "drive cycle". However, I think the refueling event may cause an error.

The (hopefully) good news is that a guy on ebay is selling new, unboxed down stream sensors for $7.00 instead of the $70 at autozone.

Seems strange that Remove&Reinstall the pipe made a difference, even settled the idle down. How did the "permanent" saved fault go away?

donbrew

Here is an update.

I put some Seafoam in via the PCV hose and let it sit overnight, put some into the oil.
A miracle seems to have occured! The P0420 has been gone for about 1000 miles, the O2 sensor seems to have settled down and the oil burning seems to have gone away.

Still can't get the evap to run diagnostic.

That $7 sensor turned out to be a random part "not as described", don't know what it fits. Got my money back fast. They do have the correct one for a very attractive price though, e-herco is the company on ebay.

donbrew

OBDII reports that there have been 6 attempts to run the evap diagnostics. Still no code, but I think one of the numbers is telling me the canister valve is stuck closed.

The diagnostic will not run if any component is not working. But, no code or CEL?

donbrew

The latest:

The EVAP finally ran, turns out they changed the "drive cycle" in 2010 (I think. I posted about that elsewhere). The alternate to running it takes "up to 17 cold starts" followed by 17 hours of rest after each cold start. My car gets to rest for only 12 hours a day.

So I replaced the #2 O2 sensor with a $15 one. Learned that "they" are correct about the cheap and/or Bosch sensors, they read low by about .4 volts. Got rid of the P0420 in exchange for a P2270 (O2 sensor signal stuck lean).

Put in a NGK #2 O2 sensor. That cleared the P2270, but as soon as the EVAP test ran the P0420 returned. Turns out the test for the P0420 does not run if there is a P2270 or a bunch of other codes present.

Also replaced the #1 O2 sensor with a cheap on, but it seems to be providing good values.
Also replaced the Purge Solenoid (under hood) The other one is in the mail as of this date.

Today's story is that I crawled back under the car and gave the NGK sensor a bit more of a twist to compress the washer a little more and cleared the codes, after 211 miles and 5 starts (not cold) none of the stored P0420 have returned. But the EVAP has not run yet either. Fingers are crossed!

Updates to follow.