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. 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?

3xGN

Tyger255, did you ever get this resolved? I'm having similar issues with my '04 throwing these same codes, runs rough at idle and especially with cooler ambient temps.

Dustin Ryan

Tyger,

I have noticed with GM vehicles they like ACDelco spark plugs only. For example, my Trailblazer would miss fire if I used anything other than ACDelco its weird. I do suggest get a better scanner, I use a Autel bluetooth scanner, it has changed my troubleshooting life. You can watch live data, see which cylinders are miss firing and it even counts how many times its missed on each one. Its packed with a ton of features. Additionally, dont rule out that just because parts are brand new they are not defective, I have spun my wheels dealing with new parts that were bad. If you did not use ACDelco or Delphi parts for plugs, wires, and coils I would do that next. Also, if you have a leak in your intake manifold it can be sucking in air causing the miss fire, you can get ether and spray it around the manifold if the idle goes up you know you have outside air coming in some where. Just be careful doing that. Also, if you have not changed your fuel injectors they could be due a change. A good scanner can show you how they are performing, which at 200k miles I would assume its a good time to change them.

Dustin