So it began once or twice, a week, then slowly got worse. My truck is a 2004 CCSB Sierra 5.3 2wd. Volant w ram air scoop, diablosport tune, New MSD coils, wired, Delco Iridium plugs, 3" dynomax bullet turned down. It will just randomly run like total ****, misfiring, skipping, particularly under a load, but if i give it WOT itll level out normally, its gotten progressively worse, and now runs like complete **** 75+% of the time. I tried swapping throttle bodies, MAP sensor, cleaned MAF. Only code it shows is random/multiple misfire. tried removing tune. could this be cam or crank sensor? stopped up cats? IM puzzled. any help is appreciated. Oh yeah, strange as it may sound, generally after misfiring and such, if I park, Exhaust smells like JB weld....odd, I know....

 

Have you changed your knock sensors and harness.....?

 

they are under the intake on this truck, correct? I havent replaced them. havent removed intake. common problem with knock sensors?

 

If you can, look at your fuel trims and how your O2's are working. I have experienced this with worn out O2's.

Edit: I just reread that you are using a hand held tuner. My guess is worn out o2's that are sending your fuel trims into a fit. Why your exhaust smells like JB weld...Cats trying to convert your fuel rich exhaust? my .02

 

intake gaskets leaking vacuum is a common problem. spray some brake clean in the intake gasket area, if the missfire gets worse, i would say you have found the problem. make sure you have rulled out any spark related issue and stay away from the coils with the brake clean. otherwise you will hear the POOFF!

 

I am looking at the word "New" in your original post. It is possible to get a defective new part. I have also encountered dumb stuff like spark plug wire cracked, broken, not fully seated, spark plug not seated, wrong plug, wrong gap, cracked shell, well you get the drift. If you can get access to a scanner to check cylinder firing or thermal could rule some things out. Also from changing the new stuff, look for loose vacuum hoses, wires, cracked plastic, etc. in the areas you worked in. Whenever something goes south on my truck, the first question I ask is what did I do to it, looking for something that actually failed on its own is secondary. cheers

 

Lets bring it back to the beginning.... forget everything else that has been posted just for right now!! You said this started once or twice a week then slowly got worse... when this STARTED to happen, what mods did you have on the truck??

Based off what you have there can be NUMEROUS things going on. All the suggestions made in this thread are definitely plausible. So in order to narrow down the issue, you need to start from the beginning of this problem. When did it start and what was on the truck when it started.

IMHO, the most plausible suggestion Ive read is from Suddog. Given that it has progressively gotten worse it sounds like an emissions issue. Usually if a mechanical part fails it doesn't really slowly progress... its more like an its there kinda then BAM its definitely noticeable. If you cant figure out when and what you had when this started, then start off by checking the O2's. Are you getting a SES light? If so what is the code!?

 

I have heard of some problems with the Msd coils. How many miles? Also check your fuel filter.

 

04 doesn't have a fuel filter except in tank. 112k on the truck, 5k on coils, may swap original coils back on and try it, but wouldn't think itd be as random as this.