running like poop!

[tsdrummerboy]

I`m stumped check engine light is on showes code p0300 which is multible cylinder misfire.I`ve changed the plugs and wires last month that fixed the problem for awhile.I put on a set of OBX stainless long tubed headers w/ hi-flow cats(don`t think that should cause anything....) by the way cost me$650.00. But after the install the engine light came back on.The light comes on then starts blinking,then stops,then goes off,then....repeats.Ran a code check again showing the same as written above.It seems when I start to accel the engine runs "ruffer" it even backfires.That`s when the engine light starts to blink.Water temp stays within normal range.I check all the plug wires,they`re on tight.Coils and injectors are, I believe original.I have about 83000 miles on an `03.....Any help/ideas?????
thanks,
tim h.

[adamk85]

I would check plugs and wires real good, making sure a plug is not cracked it will have a carbon stripe on it if it is cracked. If it is not a plug or wire then i would do an injector balance test.

[tsdrummerboy]

sounds good,thanks for the info.

[hummeraddict]

could the headers and cats throw off the sensors?

[tsdrummerboy]

You were right I had a cracked spark plug,changed it out and the Hummer is running better,.....for now,lol.So again thanks for the info.I must have cracked the plug when putting the header on.

[NJ H2]

How do you like the OBX Headers?

[tsdrummerboy]

so far everything is great with the headers.They`re long tube,come with the high flow catts and the best part....they bolted right up.However I did run a true dual exhaust system.....sounds great with flow master 40`s.And I thought the price was pretty good too.I got mine off of ebay. $675.00