Random Misfire (P0300) and o2 sensor codes!!

[LongrangeLauber]

Okay this is driving me crazy as I can normally figure most things out myself. Truck is a 2014 Silverado 1500, 5.3L (L83)

 

I am getting a P0300 code as well as these o2 sensor codes: P0030, P0031, P0135, P0137

 

Truck was running 100% fine until Monday morning (6/21). Leave my house to head to work and I get on the main street to get to cruising speed. Truck pretty much feels like it goes into limp mode, I lose all power, for about 4-5 seconds or so. Then it downshifts to 2nd or 3rd, and I cruise most of the way to work without issue. Stop for coffee, hop in the truck, runs fine all the way to work, but about 2min from work I get my CEL on the dash. Didn't have my scan tool so waited until I got home. Pulled codes only for the upstream driver side sensor and then cleared them. They came back this morning, and now this evening the truck seems to be getting worse and almost sounds like it's about to stall out at times. That's when all the other codes popped up alongside them. 

 

Only thing I can think is there may be water in the fuel. Last time I filled up (Saturday, 6/19) I filled with the 88 octane stuff from Sheetz (believe it says up to 15% ethanol as opposed to 10% in the regular gasolines) and I still had a little over 1/4 tank when I filled up. I've ran that fuel for many thousands of miles with no hiccup (truck is FlexFuel capable) until this week. 

 

I picked up a new upstream o2 sensor tonight and that's when the truck started acting up more. On my way home from the parts store that's when I thought about possible water in the fuel, so I stopped at a different station and filled up with regular 87 octane; at this point I burned a little more than half a tank, added about 17 gallons on this fill up.

 

At cruise speeds it runs perfectly fine, will downshift when I hit the accelerator too, but sometimes it sounds like it is struggling trying to get to those cruise speeds.

 

Is it just coincidence that the truck started acting up after I filled up last? Or should I actually go ahead and replace the o2 sensor and see if that changes things? Would rather not just throw $$ at it in hopes of fixing it, but sometimes it beats having to drive all the way to the dealer plus taking time off from work.

 

Any input would be awesome, thanks all!!

 

 

[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 

[LongrangeLauber]

I will add this, since I've installed the new OEM y-pipe assembly, I've driven approximately 300 miles. My miles per gallon have gone up about 1- 1.5 mpg since then. Even lifted on 35s with 4.56 gears, I'm now averaging about 15.5-16mpg around town (slightly lower on the highway.) Yes, the speedometer is corrected for the gears and tires. I dialed it in perfectly based on GPS speeds and GPS distance driven. I know the computer is a little exaggerated with the mpg claims, and based on previous calculations it reads approximately 0.5 mpg better than actual. So realistically I'm getting about 15-15.5mpg. Still better than 13.5-14 mpg (hand calculated) when I had the 420/ 430 codes logged in the computer.

 

Need to take it into a shop and get this emissions test done finally