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Random Misfire (P0300) and o2 sensor codes!!


LongrangeLauber

Question

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!!

 

 

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Nice! Guess that Magnaflow had some flow issues is what it sounds like. Good deal!  With fuel prices the way they are, it should cover the cost of the Y-pipe in about 90 days. 😁

 

That's impressive mileage! I'm on friggin stock 20" wheels, Corsa cat back, K&N cold air intake, and a Hypertech canned tune, and I haven't seen 15 unloaded in years. Towing I've been 10-11. Abysmal! I've got a Truck Norris cam and a bunch of other goodies sitting here waiting for my Magnuson supercharger to get here - saying it should ship end of June (Ordered mid March! 😒). Hopefully that gets me better mileage towing, since I won't have to keep it close to the rug for long periods of time. We shall see. 

 

I'll probably just start towing at 80 and send that all out the window. 😂

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Just thought I would add to this thread. 2018 Silverado 5.3. Had random misfire codes.  Replaced O2 sensor with NTK branded one. Problem persisted and actually got worse ( hind site is 20/20 here).  After unnecessary swapping parts found this thread. Removed new NTK sensor and replaced with OEM. Problems resolved. 

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