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!!

 

 

[asilverblazer]

All those codes point to a failed O2 sensor (except the mis-fire code) so I'd start with a new sensor. That sensor detects Air/fuel ratio, so if it is having a problem it can throw off how the engine runs. I think the re-fueling is just coincidence.

[LongrangeLauber]

21 minutes ago, asilverblazer said:

All those codes point to a failed O2 sensor (except the mis-fire code) so I'd start with a new sensor. That sensor detects Air/fuel ratio, so if it is having a problem it can throw off how the engine runs. I think the re-fueling is just coincidence.

Yep, that’s what it was. Replaced bank 1, sensor 1 o2 sensor and it cleared up all the codes. Now I’m getting the dreaded p0420 code

[Jsdirt]

Misfires may have melted the cat. Surprised it happened that quick. Usually you can drive around with a dead miss for a little bit before it fries it - like a couple thousand miles. I'm fairly certain GM probably cheaped out on the cats, as they do with every part these days.

 

Plus it was sounds like it was a severe miss - that will make the cat glow. Even the old car's cats didn't last too long after a few thousand miles of that. These days I don't think you can drive 100 miles in that state without a complete meltdown of the cat.

 

Hopefully it's just the downstream sensor failing. Watch it on the scan tool - once warmed up, the voltage should stay steady, and not fluctuate like the upstreams will. Usually .600v -.800v. My '07 seems to stay around .650v - .750v.

[asilverblazer]

I've tried the spark plug anti fouler tricks with no success. I agree that newer cats are very sensitive to failure. I'd for sure run the truck a while to make sure it is in fact running properly before replacing the cats. Also, seems like the emissions system used to have an extended warranty... 10 years, 100k miles. I'd at least look into it.

[LongrangeLauber]

I’ll have to watch the o2 sensor voltages and see if the rear one is failing, but I’m fairly certain I melted the cat. I drove a little over 100 miles with it doing that, knew I should have parked it when it first happened

[Jsdirt]

Ahh that sucks. 

 

MA just screwed me big time. We used to have a rolling 15 model year emission exemption (anything 15 model years old or older), and the pricks just reversed the law on me, just one damn year before I was due! Now, all 2007 and newer vehicles need emission testing until they get scrapped. What a screw job. I hate this f'ing state ... 

[LongrangeLauber]

So update on this issue since it's been about 6 months. 

 

P0420 code is still there and I'm due for emissions this month lol. I have a replacement cat for bank 1 that I need to have welded in. I am also getting a P0430 code, so hopefully the other one isn't failing too. Guess I'll see once I get the first one replaced.

 

Truck definitely drives different with any emissions codes logged. I had my battery unhooked for a few hours the other day and it "cleared" the codes temporarily. Truck seemed like it had more giddy up than what I have been used to for the past 6 months. It also shifted a lot smoother too. Whether that is related to the emissions issue or if the TCM got reset as well is beyond me.

[Jsdirt]

I think the newer trucks use the post-cat sensor for fueling, unlike in the past where it was just a tattletale for gutting a cat. When it's not working properly, it probably takes that downstream o2 data and changes fueling. That's my theory on the way it runs, anyway. Sucks, but it sounds like you're probably going to need both cats. Sign of the times, unfortunately.

 

 

I just turned 117k miles yesterday. Drove that thing more this year than since '09 when I was commuting. Made 3 trips down South this year in addition to my usual New England circuits. Anyway, my oil pressure is steadily dropping off. Just on yesterday's road trip I noticed a slight change for the worse at idle sitting at a light - just slightly below that first unlabeled line! Won't be long before it throws the money light on for low oil pressure, then the engine fails soon after. I've never owned a more expensive, unreliable pile of crap in my life!! 

 

It's not making noise yet, so it's got some life left. The gauge is notoriously inaccurate, but it's following RPM like it should, so that tells me the sender is good, and screen is not clogged (shouldn't be, since I've always run the best of the best oil and changed it often) -it's just trending MUCH lower than when the truck was new. I'm also running 10W-30 vs. 5W-30 ...  and it's winter. Not good. With 10W-30, I used to be over the 40 mark at ANYTHING just above idle, and close to 80 when accelerating cold. Now cold, I never even reach 40! I suspect the #2 cam bearing is just about all the way out of its bore, based on past oil analysis. It's days are numbered ... 

 

[LongrangeLauber]

53 minutes ago, Jsdirt said:

I think the newer trucks use the post-cat sensor for fueling, unlike in the past where it was just a tattletale for gutting a cat. When it's not working properly, it probably takes that downstream o2 data and changes fueling. That's my theory on the way it runs, anyway. Sucks, but it sounds like you're probably going to need both cats. Sign of the times, unfortunately.

 

 

I just turned 117k miles yesterday. Drove that thing more this year than since '09 when I was commuting. Made 3 trips down South this year in addition to my usual New England circuits. Anyway, my oil pressure is steadily dropping off. Just on yesterday's road trip I noticed a slight change for the worse at idle sitting at a light - just slightly below that first unlabeled line! Won't be long before it throws the money light on for low oil pressure, then the engine fails soon after. I've never owned a more expensive, unreliable pile of crap in my life!! 

 

It's not making noise yet, so it's got some life left. The gauge is notoriously inaccurate, but it's following RPM like it should, so that tells me the sender is good, and screen is not clogged (shouldn't be, since I've always run the best of the best oil and changed it often) -it's just trending MUCH lower than when the truck was new. I'm also running 10W-30 vs. 5W-30 ...  and it's winter. Not good. With 10W-30, I used to be over the 40 mark at ANYTHING just above idle, and close to 80 when accelerating cold. Now cold, I never even reach 40! I suspect the #2 cam bearing is just about all the way out of its bore, based on past oil analysis. It's days are numbered ... 

 

No code for oil pressure sensor? Replaced the one in my dads 09 about 6 months ago. Apparently the gmt900s are notorious for the oil pressure sensor failing and the oil pressure sensor screen/ filter gets gummed up easily. His truck has 325k miles on it and he also runs 10w30. Definitely worn out but she’s still kicking!

[shakenfake]

13 hours ago, Jsdirt said:

I think the newer trucks use the post-cat sensor for fueling, unlike in the past where it was just a tattletale for gutting a cat. When it's not working properly, it probably takes that downstream o2 data and changes fueling.

No even in the newer trucks it does not use post-cat sensor for fueling.

[Jsdirt]

14 hours ago, rdnckhntr94 said:

No code for oil pressure sensor? Replaced the one in my dads 09 about 6 months ago. Apparently the gmt900s are notorious for the oil pressure sensor failing and the oil pressure sensor screen/ filter gets gummed up easily. His truck has 325k miles on it and he also runs 10w30. Definitely worn out but she’s still kicking!

No codes yet. The way it tracks pressure with RPM the way it always has leads me to believe it's telling the truth. The only way to be sure would be to hook a gauge to it, but I haven't been that motivated just yet. Back at 70k, the engine was making so much metal, I never dreamed it would last this long anyway. Just a matter of time, I figure. I highly doubt I'll see 200k without a major failure, let alone anything in the 300k range.

[Jsdirt]

1 hour ago, shakenfake said:

No even in the newer trucks it does not use post-cat sensor for fueling.

I've been hearing the opposite, but that may be with cars - maybe the trucks are different. Not sure there. I know there's several brands that started using post-cat sensors for fueling starting around either '06-'07, or 2010. Friggin manufacturers can't stick to ONE thing, so it's impossible for me to remember all of it across every brand, and every model out there. It's mind boggling these days.

[LongrangeLauber]

9 minutes ago, Jsdirt said:

No codes yet. The way it tracks pressure with RPM the way it always has leads me to believe it's telling the truth. The only way to be sure would be to hook a gauge to it, but I haven't been that motivated just yet. Back at 70k, the engine was making so much metal, I never dreamed it would last this long anyway. Just a matter of time, I figure. I highly doubt I'll see 200k without a major failure, let alone anything in the 300k range.

My scan tool gives me oil pressure readings, assuming the sensor is operating correctly

[Jsdirt]

Yeah, bad sensor, bad readings. I need to put a gauge directly into the block and see what's really happening. I haven't looked at the scan tool for that reason. 

 

Every time I take a road trip I have to bring the scan tool with me to do a fuel composition reset, otherwise I get 9 MPG towing the flatbed, loaded. Constantly creeps up from 3% (lowest it can go) to well into the 20% alcohol content range. It calculates alcohol content based on an algorithm. What a stupid assed way to engineer something! Typical GM ...

 

I don't know which is worse - this dumb system, or the failure prone alcohol sensors on the older models! Can't win either way ...

Edited December 9, 2021 by Jsdirt