2003 Sierra 5.3 Random Misfire and O2 sensor codes

absinthminded · October 11, 2016

So, I have an 03 Sierra 1500 with the 5.3L 212,xxx miles. Saturday I noticed a coolant leak. I did some digging and found that my water pump (or gaskets) had failed and dumped coolant all over my driveway. I swapped in a new water pump (napa lifetime warranty) and took it for a shake down drive. Its running really rough. Check engine light is blinking and the engine is missing. I changed out plugs and wires today and there was no change. They were old and I figured they were due.

I ordered a new coil pack. Just waiting for it to come in.

I ordered 4 Denso O2 sensors (they might be original)

I have yet to test the fuel pressure.

Injectors might be dirty?

Fuel filter was changed 2/3 years ago.

Fuel pump is original.

My wife needs to drive it to Chicago this weekend. Where should I start?

Thanks for your help.

Tuckybutt · October 11, 2016

Did the truck run fine prior to putting the water pump in?

absinthminded · October 12, 2016

Yes, it ran well before.

txab · October 12, 2016

Why not read the stored codes? Check the MAF and connections. Also check all intake connections for leaking air. Check any and all electrical connections in the areas you were working

absinthminded · October 12, 2016

Will do. I had the codes read but the guy didnt tell me what they were as far as code number. He just said random misfire from the right bank and the O2 sensor code. I will check the connections again. I can just spray carb cleaner around the connections? I've never cleaned the MAF.

absinthminded · October 13, 2016

Today I installed 4 new DENSO O2 sensors. No improvement. Then I took the MAF out and cleaned it. I cleaned the rubber connectors at the MAF, air box, and throttle body. Re-installed and snugged them down tight. No change. I checked wire connections and I didn't find a smoking gun. The one thing I forgot to mention was that I put a new pcv valve in when I did the water pump. I don't see how that could be related.

Colossus · October 14, 2016

Need to get a scope/tech II on there and see what it is doing. But try this first, for kicks sake- pull out the plugs and plug wires, verify the gap on the plugs, I cant remember if on the 99-03 models if each cylinder had it's own coil pack or not, or if each side had a coil pack (4 plugs for 1 coil pack) I know you said you replaced one coil pack, but could the other one be bad as well? I'm betting with that kind of miles it is or very close to it. Make sure everything is dry and cleeeeeeeean. Let's see how that does. By the way, I like the pic! I had a 05 Sierra those same colors that I traded in for my 2008 Duramax years ago. the second time I purchased it (long story, don't ask) I miss the 2-tone paint I had on that 05 and my old 99 Silverado.