I got a sierra with a 5.3. Has several aftermarket parts. Got into it yesterday. Afterwards I noticed my truck was missing. I haven't had a whole lot of time to check many things yet just trying to get a good starting point. It misses at idle. If I'm running around 2k rpms you can hear it kinda sputtering like witchever cylinder is missing is somewhat trying to fire. At WOT it "feels" as if it is running on all 8. Any help would be appreciated. It's not smoking or making any funny noises. Does this sound like maybe a fouled plug? I'm getting fire through all coils and wires. Thanks guys

 

Id start with checking out the plugs and wires then move to coil pack connection's...

What are the mods on the truck??

 

Need more detail?? What Year is it? Mods? It could be a number of things. Spark plugs and wires at idle maybe..but I doubt it, normally those things will be noticed uder a load unless the spark plug is heavily carbon tracked. If I was guessing, sounds like you got some dirty injectors or possibly bad fuel, but like I said more details. Check Engine Light On? Returnless Fuel System or Not? Let us know.

 

It's a 01. 5.3. Stock rebuilt lower end. Ls6 high volume oil pump. 241 heads p/p. TS224r cam. Pacesetter long tube. MSD wires. Airaid CAI. Harland Sharp rockers. Ported throttle body. Build has about 7k miles. Not sure about the return fuel thing you said

 

No check light on yet. Have only drove it maybe an hour since it happened. A buddy of mine is saying he thinks I might have broke a valve spring

 

I doubt its as broken spring but a quick pull of the valve covers will comfirm this

 

You said, after you got into it?

If you can scan it & watch active misfires while it's idling & missing, you may be able to narrow down which cylinder it is. Otherwise I'd start with a compression test, and go from there.

 

Broken valve spring! Here's the problem.....heads were assembeled when I bought them from an individual. Has Harland Sharp rockers. Is there anyway to know who made the springs??? Is has the double springs. Outer one is broke. Help!!

 

I'd just buy a new set of springs & be done with it. No way I'd just replace the broken one & run the rest of them.

 

Ordered some new springs. Anyone in the south fort worth area have a stock 241 spring that I can buy? Need to put it on temporarily till I get my new springs. Need to my truck to get to work.