Help Im running outta Ideas....

[DirtyRedScottsdale85]

So guys im new here and I hate that my second post has to be a question like this but i really need help or input....The truck is a 2003 Silverado Z71 5.3L with about 128k

 

So on my way home from a shooting comp. last weekend as a tried to pass a few cars I noticed that I was lacking some power, then about the same time my CEL started to bling at me and the truck wouldnt rev past 3500-4000rpm. After slowing down, the miss, as it seemed, went away only to do it again after after i pushed the throttle past 1/2 way.

 

Now the truck runs fine up until you push it past 1/2 throttle or put it under a heavy load. The CEL ended up being MAF sensor performance and Random misfire...I have done the following: Cleaned TB, replaced the MAF, the plugs and wires are less than a month old, Ive checked for vaccum leaks (lines and the intake gaskets)..... All with no result... I plan on changing the fuel filter this weekend....

 

Sorry for how long this is.

 

Now here is where im stumped, after datastreaming it on the way home from work i noticed that at full throttle around 3500rpm it starts missing, But only on bank 2. with cyl 6 having the most. But bank 1 doesnt show a single missfire.. So my main qustion is what would cause bank 2 to only missfire under a load, with bank1 prefectly fine?

 

 

HELP!!!!

Thanks in advance

[SILVERADOSC540]

Could be plugged cats.

[Carder09]

Have you tested the fuel pressure yet?

[DirtyRedScottsdale85]

Haven't done that yet ran outta time at the shop after work. And as far as a cat I haven't ruled that out yet but the secondary o2s are reading around the same mv's on both sides. Any possibility that fuel pressure could be less on one bank?

[KMGZ400]

i had the same exact issue with my 2003 miles at about 115,000 miles which i saw you had about 120 in your other post.

 

it was my cats. its gonna be expensive, get ready to pay big $ unless you can do it yourself. change you fuel filter too so the new cats dont get clogged again. luckily you have an 03 so you have an external fuel filter

[kstruckcountry]

If it's cats and you don't have exhaust inspection, ditch them and have a shop replace with pipe. Problem solved.

[DirtyRedScottsdale85]

Gonna try a few things today after work. And as far as cats go I work at and exhaust shop as and inspection mechanic so wether I just ditch the. Or replace one its not a big problem. Just gotta find the time

[DirtyRedScottsdale85]

Sooo.... Got off work a little bit ago and decide to mess with it a little before I went home( only had a few minutes gf was making ham pot pie can't miss that). I figured if it I the cat instead of slapping one it and wasting the money if it doesn't fix it, I'll drill some holes just big enough that I can still weld shut after the fact.... Soo I did just that, then closed up and left to go get me some of the ham pot pie... After I turned outta the shop I slammed on the gas and to my suprise it ran like a champ all the way to 5000 and the graves 2nd... .... Soo looks like I'm replacing the cat, or deleting them both...

 

But.... Cats just don't go bad so next step is to ind wat caused it to clogg. Thanks too all ill keep posting on what I find next.

[kstruckcountry]

Cats do clog eventually. Glad it was such an easy fix. If it was me I'd replace them with pipe, unless you can get a killer deal on some.

[DirtyRedScottsdale85]

I get them for cost, but ill most likely just cut em both out and put in some pipe... I know a good state inspection mechanic ;)

 

[kstruckcountry]

Hahaha. If you want it to appear as though you have functioning cats, I know you can just bore them out and put them back on.

[DirtyRedScottsdale85]

Haha yeah I've done that in the past... But being that I'm gonna be the only one looking at the underside of this truck till it sees 200k ill just weld in some pipe. But don't tell no one ha

[kstruckcountry]

Your secret is safe here. Luckily no inspections in Kansas.

[DirtyRedScottsdale85]

Yeah be glad u don't have them.

[gmtech4]

stop pissin around and do an exhaust pressure test in the o2 sensor after the cats ,if its higher than 3 ,they are plugged ,,,,thats how ya do it boysssssss