02 Tahoe 5.3 multiple codes come and go, weak performance

02 Tahoe 5.3 has about 175k on it


A while back had the CEL come on... my wifes car, shes not the quickest to point out issues. Not sure how long it was going on.

No noticeable performance changes though

Came to a head this last summer when we had to go thru emissions and failed because of the CEL.

Not having the time or money to sort it out, we took it to an emissions shop to get a waiver (in WA you can 'spend $150 diagnosing/repairing an emissions failure' and get a waiver)

Shop ran codes, P0300(random misfire) and P0430(bank 2 cat efficiency low)
Stored codes were P0135 (o2 sensor circuit) and P0171 & P0174 (lean bank 1 and 2)

Said that he found that the misfire had been a one time event about 6500 miles prior and that ALL 8 cylinders "had heavy misfires at the same time" and nothing since then.

Since we were there to get the waiver and nothing more, we left it at that.


I cleared the codes and drove for another few thousand miles and the P0300 and P0430 were the only codes to come back. I erased again and only got the P0430 this time.


So definitely an intermittent misfire and a bank 2 cat issue

Neither of us noticed any performance issue until last week when we bought another Tahoe, a 2006 also with the 5.3
This new Tahoe is a damn nascar next to the old one.

I cant believe the difference, both being mechanically built the same and within 25k miles of each other.


What can I take from this? Is my 02 Tahoe simply needing cats soon?

Did the misfire smoke the cats or did clogged cats create a misfire?

How can can I test these cats without just replacing them and seeing what happens?

Dont want to get new cats and have the misfire smoke those too...

IMO, the misfires contributed to a cat(s) problem. How old are all the tune related components? You can get a back pressure test on the cats. You can get an infrared temp gun and report here the temp readings at the inlet and exit of the cat(s), after the engine is completely warmed up. The loss of power is likely a clogged cat or two. If you do the cat(s) replacement you should do the O2 sensors as well.

https://www.rockauto.com/en/moreinfo.php?pk=388841&cc=1380372&jsn=2248

https://www.rockauto.com/en/moreinfo.php?pk=89390&cc=1380372&jsn=2268

https://www.rockauto.com/en/moreinfo.php?pk=89376&cc=1380372&jsn=2273


If you are doing the cat(s) and sensors you should also do the plugs and wires and fuel filter and clean the MAF and do the air filter if needed.

I just went through the records I have (going back to when it was new...) and I dont see that the plugs have been done.... ever.....

I thought they had been done before I bought it, but cant see that anywhere.

Anyhow, Ill pull a couple of them today and see how they look. Ive already ordered replacements either way.

Plugs and wires are probably done for but typically they dont get better just like cats usually dont either so this is a very weird one.

"Said that he found that the misfire had been a one time event about 6500 miles prior and that ALL 8 cylinders "had heavy misfires at the same time" and nothing since then."

Im gonna have to raise the BS flag on the fact that the mechanic could tell you how many miles ago the incident happened. I have a tech 2 scanner and it wont even tell you that info and I dont believe the PCM will even store info to that degree. Someone else wanna chime in on this one to verify?

I think Ron nailed it (as he seems to always do) but you should also look to see if your intake manifold gasket is leaking. It's a pretty easy fix and worth trying if you're not sure.

Two follow up questions...


1. Checking for intake leak, just shoot carb cleaner around and listen for idle changes or is there another/better way to check?

2. Plug wires.
There seems to be two styles out there. Each one being for coils stamped with diff numbers.
I dont see any markings on my coils... Do I need to remove them to see this?
OR
They are either 10in or 12in . is this measured boot to boot or in between boots?

Shibbershabber said:

Two follow up questions...


1. Checking for intake leak, just shoot carb cleaner around and listen for idle changes or is there another/better way to check?

2. Plug wires.
There seems to be two styles out there. Each one being for coils stamped with diff numbers.
I dont see any markings on my coils... Do I need to remove them to see this?
OR
They are either 10in or 12in . is this measured boot to boot or in between boots?

Click to expand...

You will have the round or square coils. The round coil takes the shorter wires.

https://www.rockauto.com/en/moreinfo.php?pk=340523&cc=1380372&jsn=2230 These are for the round coil.

https://www.rockauto.com/en/moreinfo.php?pk=340527&cc=1380372&jsn=2231 These are for the square coils.

I also agree with Mike. If that tech has something to pin oint what he was saying as to the mileage and such, I would like to see it. Not saying it isn't possible but I have never seen something like that.


As far as checking for vacuum leak at the intake and surrounding area, you can use a squirt bottle of water instead of carb clean and get same results.

I use my mechanic's stethoscope and just take the wand attachment at the end and pull off the wand and amplifier that it is attached to and use the long flexible hose as my ear and I run it around the areas I want to check. You will be amazed how well you can hear a vacuum leak. Create one and test it to see.

Sprayed around for the intake leak and didnt notice anything.

Plugs and wires made a big difference though. Acceleration is a lot better now.


I havent erased codes yet to see if it comes back. Assuming the cats are still a mess Ill get the same code.


Thanks

P0430 is a cat code, you have a bad cat, not a false positive because of something else. If it was a bad sensor, there are codes for that too. If the cat has broken media, it may cause a temporary blockage which caused your temporal misfires, but I am just speculating there but we often see random misfires associated with a bad cat. Conversely, we also see misfires cause a cat to fail. So IF there's a coolant leak, bad plug, injector, etc. such can cause a cat to fail, usually the case.

Don't skimp and get some Chicom cat. You'll be replacing it sooner than later.

Here's my story: AFM went bad at 111K and took out one cat. Cheap Chicom welded in. Within 6K miles that cat started throwing intermittent codes for a few thousand miles and finally the other one. Replaced the whole Y-Pipe with Magnaflow system at 124K. Tech-2 allowed me to analyze it to death and kick the can down the road.