2005 avalanche missing and backfiring HELP!

HELP! I have a 2005 Chevy avalanche 5.3L 327. It has 79000 miles but neverhad the 60 thousand tune up. I did spark plugs on it but that made it runs even worse, I bought new ngk iridiums and new wires. I starter the truck when I was done and It ran like shit barely at all... missing and backing like no other, I put the old plugs back In and it ran fine for the rest of the day. After that It ran like shit again. The part that confuses.me Is It runs fine until the engine gets warm then it barely idles and Is missing and backing again. The engine light is on and some times when I stomp on It the engine light flashes 17 times, sometime it flashes when I just start going, or am just going up a hill. The enging Is having a major drag and Im just stumped... I need help this truck is my daily driver and I still owe 16000 dollars on it, I cant afford much or to lose this truck. I'm pretty engine savvy so I know what most everything is.(note plugs on entire left side of engine are comin out pretty covered in carbon, I run straight pipes for exhuast and sometimes when I stomp on it it spits black smoke out the back)
Truck also turns over really slow when cold, new battery less than a year ago...

Also truck is only gettin 11mpg I'm filling my gas tank every two days I cant affored this and taking the truck to chevy Is not an option I CANNOT afford it

If the engine was running fine before you changed the plugs and wires then you must have crossed two of the wires.

None of the wires are crossed everything is the way It shoild be, possibly a fuel filter? Or could it be oxygen sensors?

Complete your tune up!
1) New Air/fuel filter
2) New upstream HO2 sensors.
3) Clean the MAF sensor.
4) Disconnect battery from your truck
5) Touch the pos end cable to ground to reset the ECU/PCU (computer) and control modules.
The ECU needs to relearn with new parts.

How cold is it in Alaska?

the past couple days its been getting dow to about -3 at night here in anchorage...

Digital dash, electric fuel pump, ignition, starter takes alot of battery power!
Your engine block is below freezing, it might be time for a block heater.

i thought the 05's had block heaters on them?

yea my truck does have a block heater onn it by why would it be starting slow now?? battery leak? its never done this before... not even on the days where it got down to -20 last year

do you think maybe its acting funny becuase when i put the new plugs in i never reset the ECU? its never had the computer and electronics reset its entire life.

Complete your tune up!
1) New Air/fuel filter
2) New upstream HO2 sensors.
3) Clean the MAF sensor.
4) Disconnect battery from your truck
5) Touch the pos end cable to ground to reset the ECU/PCU (computer) and control modules.
The ECU needs to relearn with new parts.



How cold does it need to get for the block heater to turn on?
Bad fuse/relay/heater element/temp sending unit

Pitch the NGK's in the trash. Use AC Delco #41-110 plugs with a gap of .040
After replacing the plugs, retrieve the DTC's and post them here in the order they are retrieved.

No need to disconnect the battery. Disconnecting the battery will only turn the SES light off if there are no hard faults present. It will not clear the history file or reset fuel trim. A bidirectional scan tool is required to clear the history file and reset fuel trim. Resetting long term fuel trim is not necessary after a tune, it will relearn as you drive.

It currently has the old ac delco plugs In It, I just need it to stop missing and sputtering, you think maybe a new fuel filter would do it? Oh and plugs on left side of engine are coming out covered In carbon,I also get the occasional cloud of blacksmoke that comes outta the exhaust

Very doubtful the fuel filter is causing the problem. Guessing wastes time and incorrect guesses cost money. The PCM is a powerful piece of test equipment, Autozone and Advance Auto Parts will check it for free. Have them retrieve the DTC's and post them here in the order they are retrieved.

All I have for auto part stores here are oriely auto parts and napa I dont know if they would do it ... especially since everyone here charges an arm and a leg for everything

Looks like you have 4 Schuck/O'Reilly stores in Anchorage, give 'em a buzz and ask them.

No One in anchorage does pcm testing...

There's a Wal*Mart in Anchorage and they have code readers for about $55. Then you'll have it and you can check it yourself any time you want. It's an entry level reader, and it will give you the DTC's.

http://www.walmart.com/ip/Innova-3030-CanOBD2-Maintenance-Indicator-Car-Reader/13029622

I wounldn't throw away NGK Iridium plugs!
Ouch

Trash 'em or return 'em ;) they're no good in a GM engine. That's how NGK got its name, No Good Kind!