P0300, P0134, P0135

[Tyger255]

2003 Suburban 5.3 with 200k miles. On vacation this past weekend and I start feeling a slight miss fire, driving the 20 or so miles to get back home and it gets worse and worse till its very noticeable and constant when driving. The next day I buy a scanner and its showing these three codes. P0300, P0134, P0135. Last year I did new plugs, wires, and coil packs, so Im thinking the O2 sensors could be causing the miss fire code. So I buy both upstream O2 sensors and replace both clear the codes and no change. As soon as I start the suburban I can feel the miss fire. I do a quick loop around the block and all 3 codes come back. I pull a few spark plugs just to see what they look like, they look normal for a year old plug. Start the unit and pull plug wires, I can hear each coil firing. I check the O2 fuses in the box under the hood, they are both good. Battery voltage when running looks ok, I have not ohm any wires or checked any voltage because I was out of town at the time and have very limited tools. Now Im back home that is my next step but I do not think I'll find any problems there. Wires looked good (what I could see), plugs going to O2 sensors looked ok, hell, the O2 sensors I pulled out look ok. I could tell one was replaced at some point. I was wondering if it could have been some bad gas, I added some not to long before this started, but my buddy filled up at the same place and is having no issues. I even added 10 gallons of premium and some Seafoam to see if I would see a change it how it was running and I did not. I would love some advice from someone smarter than me. Im not sure where to go from here. All my googling so far, with what I have eliminated starts pointing to the PCM, but if the PCM went out would it run at all? This thing ran like a top just before this happen.

IF it is the PCM, if I get one from a salvage yard does it have to be programmed to the VIN? or will it plug and play?

 

[79jasper]

Not the pcm.
O2 sensors will never cause a misfire. Intake gaskets will. Look at the plugs going into the coils and injectors.

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[Tyger255]

Not the pcm.
O2 sensors will never cause a misfire. Intake gaskets will. Look at the plugs going into the coils and injectors.

Sent from my SM-N960U using Tapatalk

The few plugs I pulled looked ok, but I bought another set to change them before I checked the current ones but did not because the current ones I looked at looked ok and I replaced them all just under a year ago. I hate to throw $80 of new plugs into it if thats not the issue but I will swap them all and eliminate that option.

If it is the intake gasket, I should be able to spray carb cleaner around it and here it rev up if there is a leak? Is there a better way to check the intake gasket?

 

[Fless]

Before you change plugs you might want to see what your long- and short-term fuel trims are with a scanner. Pull some numbers and let's see what they look like.

 

[OR VietVet]

Does not have to be carb cleaner. Can use water to achieve the same result. The fluid fills in the vacuum leak and the rpm raises and smooths out. Yes, check the coil plugs as well. You said you pulled some of the plugs. Pull all the plugs and keep track of their cylinder they came out of. Post pics of all of them, as close up as you can get. Do a compression test on all cylinders, again, in order, and list readings here. Plenty of you tube videos of how to do but should always be done with all plugs out. What brand of plugs were replaced and what brand of wires and coils?

P0134 Oxygen sensor no activity (bank 1 sensor 1)

P0135 Oxygen sensor heater sensor malfunction

For P0135 being the first having a heater circuit malfunction,is more than likely a bad 02 sensor, With a new 02 sensor, if you get P0134 you may have gotten a skewed 02 sensor, A exhaust leak or a exhaust restriction at the 02 sensor will affect its operation,Also fuel presuure needs to be within specification

If I change oxygen sensors, I use AC Delco and change all of them at the same time.

 

[Tyger255]

I changed both upstream O2 sensors with Bosch replacements. It was the only ones they had at the parts store, and being out of town I was trying to get it fixed quickly and not spend all my vacation working on it.

If I can find my laptop connector I'll plug it in and see what I can find out what the fuel pressures look like.

I did unplug all spark plug wires at the coils so I could hold them close and hear them firing. All seem to fire ok. Ill check the intake for leaks, and go from there

Thanks every one for the input! this gives me a direction to go.

 

[Tyger255]

checked for intake and vacuum leaks and didn't find any. Got with a buddy that has a lot better OBD software than I do and we found cylinder 7 and 8 misfiring with #8 being very bad. I changed plugs in 7 and 8 and swapped the coils and wires to 3 and 4 and the problem moved to 3 and 4. Swapped the coils for different ones and now its running great. I really didnt think it would be a coil being a replaced them just last year. So far I havent had any O2 codes come back.

 

[afpj]

Changing coils and eliminating misfire fixed the O2 sensor codes?