Random Misfire (P0300) and o2 sensor codes!!

[Maine2500HD]

2 hours ago, Jsdirt said:

NTK is normally really good. Owned by NGK, the spark plug company. Must've got some bad ones there - happens more than normal these days with every brand. I'll have to keep my eyes and ears open for more failures with this brand - could be a possible drop in quality.

 

The cat codes will only come back ones the cat monitor has run. No specific set time for that - it all depends on if you met the requirements for the cat monitor to run, normally cruise at 55 or higher for several miles, then a long deceleration event without touching the brakes. if you live in a congested area like I do up here in MA, it can take weeks to run.

It doesn’t really take much for a defueling event duration to read/set it. I was watching it in Live data. It can be as simple as a slight/brief lift off the throttle. The ECM will not allow the code(a) to be set during the first hour-ish? Of run time after a battery disconnect. That is to allow for a break-in/run-in of cats when they are replaced. That’s why I could make it go away for a while.

 

I’m seriously questioning if the NTK sensors are even spec’d right, or maybe were my boxed right? Had the right connectors but that doesn’t mean the sensors were right. They almost seemed like they wanted to run in a 2V range where it should only be a 1V range. 
 

I took all four back. It was wild the type of problems that they were causing. Entire bank 2 misfires, had communication errors between ECM and two different modules, varying voltage codes. Engine running in open loop for extended amounts of time (45+ min) Pretty nutty stuff.

 

 

[Jsdirt]

You could've got counterfeit parts, especially if bought from Amazon or eBay. Starting to see it at RockAuto occasionally, too.

 

I've never heard of a time frame for setting cat monitors. Guys with dynomometers can run a drive cycle to a tee, and run every monitor successfully in minutes.

 

You should break in new cats, though - just idling in the driveway is sufficient for a specific period of time. Not something I do too often. Usually people punch them out and cheat the downstream sensor. They're too friggin expensive these days.

Edited May 1, 2022 by Jsdirt

[Maine2500HD]

1 hour ago, Jsdirt said:

You could've got counterfeit parts, especially if bought from Amazon or eBay. Starting to see it at RockAuto occasionally, too.

 

I've never heard of a time frame for setting cat monitors. Guys with dynomometers can run a drive cycle to a tee, and run every monitor successfully in minutes.

 

You should break in new cats, though - just idling in the driveway is sufficient for a specific period of time. Not something I do too often. Usually people punch them out and cheat the downstream sensor. They're too friggin expensive these days.

Over the counter from Napa to my hand. Highly doubt counterfeit.

The 1 hour applies to new vehicles (and in theory when the ECM/Battery has been disconnected long enough to reset.) I hadn’t heard of it either, but it came up on research, and explains why I could make the P0430 code go away for  most of the day when I’d disconnect the battery, when it would otherwise reset regularly. 
 

The drive cycle is fairly specific and a GM thing, and is an over the road test at speeds/loads for a specific amount id time. 
 

In the grand scheme of things $800 ish for any pipe with all three Cats isn’t awful…. But I’m not excited to spend it just the same. 

[LongrangeLauber]

[LongrangeLauber]

^^ Direct from AllData

[Jsdirt]

You never stop learning in this industry, that's for sure! It's part of the reason I'm losing my fire for fixing modern crap. It's just too much info to store! 

 

Thanks for posting that - as long as I've been working on these, that's the first I've heard of that. Most of the vehicles with big time driveability complaints or major electrical problems that I see in here are from 2003-2005 lately. None of my customers own anything this new. The stuff is always changing! Impossible to keep up with the pace.

[LongrangeLauber]

Turns out I do have NTK downstream sensors (I even had mentioned that earlier in this thread, completely forgot about it.) I just ordered up two GM Genuine Parts O2 sensors from Advance Auto that will be here sometime today (gotta love same day delivery!) for a little more than $60 for both (20% discount plus $20 off SpeedPerks coupon).

 

Not saying this will solve the issue, but for $60 it's worth a shot before dropping big bucks on a new Y-pipe assembly.

 

I looked into transferring to another address in a jurisdiction that does not require emissions. Unfortunately since my tags are already dead, and it is currently registered in a county that requires emissions, I would have to pass the emissions inspection before I could even register it elsewhere. Or maybe I'm just reading the VA DMV rules incorrectly. Who knows. But this is affecting how the truck drives somewhat, so I do want to get it resolved one way or another.

 

New Y-pipe assembly will cost me about $1550 (core charge included) to purchase. I cannot return my current Y-pipe for core unfortunately since the factory cats have been cut out and replaced.

 

I will continue to update this thread until I figure out the solution.

[Jsdirt]

Nothing is easy or cheap these days. Sucks! Good deal on the GM ones, though. Hope that fixes it.

[LongrangeLauber]

Well, installed the new sensors last week and no dice (wasn't getting my hopes up on that one.)

 

So, I ordered a new OEM catalytic converter y-pipe assembly (part #: 19420276) that I picked up from my local dealership. Just installed it this morning before a couple graduation parties I had to attend. No check engine light all day and stuck the code reader on it to see if the permanent codes that were stored had self cleared. Sure enough, all DTC codes are cleared and only one monitor hasn't run it's drive cycle and that's the EVAP system. It's looking like the OEM catalytic converter assembly did the trick for me.

 

After wasting so much time and money on this issue, it seems like I have finally resolved the issue.

 

A couple take aways I learned from this:

 

1) When having to replace catalytic converters, just go straight to the OEM part and don't waste your money on aftermarket cats (between install and the cost of the cats, I would have almost paid for the OEM converter assy with me installing it on my own)

 

2) Find a reputable shop that can properly diagnose the issue. Turns out the dealership was correct when they told me the aftermarket catalytic converters were not performing their duties properly, thus the codes remained set. But, the first shop I took it to said the aftermarket cats were performing their duties properly and thus they never revisited them as a potential issue.

 

 

 

I'm a little upset I had to pay for not only the OEM cat assy but also the aftermarket cats as well, and labor to install them, but I learned a valuable lesson for future vehicles. I can finally quit riding around on dead tags and not be worried about possibly getting a ticket for them.

 

Definitely a learning experience that I hope I never have to go back through again. I hope someone in the future finds this thread and it helps them out before they throw a bunch of money at their truck like I did.

 

Thank you all for chiming in with your thoughts and opinions along the way as I struggled (along with an independent shop) to diagnose this issue!

[Jsdirt]

Wow, what a shitshow! Glad you finally got it taken care of. Sucks you have to spend all this money all because of the damned government. Rotten SOB's - hope they all rot in hell.

 

My take is the downstreams ARE factored into fueling, otherwise there's no way a cat can cause a misfire code, unless it's completely stopped up solid. That's good to know, since I'd have never thought that in a million years. 

 

Thanks for sharing, CJ - some great info here!

 

This just reminded me of a '00 Jimmy I bought off eBay in '08. Had a cat code almost immediately after rolling off the transport trailer.  Had an aftermarket cat welded in. Someone warned me back then not to install another aftermarket one, so I bit the bullet and dropped $550 (That was A LOT of money to me for a friggin Y-pipe back then!) on a new Y-pipe / cat assembly. The 0420 was gone after that  ... then 15 more unrelated codes came up, and 2 years after I bought it, this is what I did to it out of  frustration. It's parts are all over the world now, lol! 

 

 https://postimg.cc/ZBD7mCt8

Edited May 22, 2022 by Jsdirt

[shakenfake]

2 hours ago, Jsdirt said:

My take is the downstreams ARE factored into fueling, otherwise there's no way a cat can cause a misfire code, unless it's completely stopped up solid. That's good to know, since I'd have never thought that in a million years. 

Down streams are not factored into fueling.

 

Glad you got it figured out bud sucks but it is what it is.

[txab]

What brand aftermarket did you try?

[LongrangeLauber]

7 hours ago, txab said:

What brand aftermarket did you try?

 

Magnaflow part #51206

 

https://www.magnaflow.com/products/51206-catalytic-converter-magnaflow-oem-grade-federal-epa-compliant-universal-catalytic-converter

[Jsdirt]

9 hours ago, shakenfake said:

Down streams are not factored into fueling.

 

Glad you got it figured out bud sucks but it is what it is.

DELETED ...

 

I went back and refreshed my memory - it was his upstream o2s that caused the miss originally.  So downstreams do not factor into fueling. Thanks for the info. 

Edited May 22, 2022 by Jsdirt

[LongrangeLauber]

8 hours ago, Jsdirt said:

DELETED ...

 

I went back and refreshed my memory - it was his upstream o2s that caused the miss originally.  So downstreams do not factor into fueling. Thanks for the info. 

Didn't have time to chime in earlier when I saw the notification but yes, this whole issue started with a failed upstream sensor.

 

Now that I know the damage that a failed sensor can do, as soon as I see a CEL come on and driveability suffer, I'm pulling over and parking it. Cheaper to pay a tow bill at that point