03 Silverado Long Tube Headers

[jackd]

2003 Silverado Z71 EC, 5.3 auto
Installed CAI and borla exhaust along with Diablo Tune and the truck ran amazingly well.

Couple of weeks later, installed Pacesetter Long Tube headers with "no cats" y-pipe and the truck now runs like it has a 10,000 lb trailer behind it. Is this because the parameters are out of range for the headers and just need a custom tune? Planning to custom tune anyway, but wasn't expecting a huge power loss after header installation.

[mikel]

you definitely need a custom tune, but you may have another issue, no codes?
pinched O2 wires, etc?

[jackd]

you definitely need a custom tune, but you may have another issue, no codes?
pinched O2 wires, etc?

I just checked again for codes, there are no codes, and the light is not on which is another thing that confuses me. The whole story: This is my brother in law's truck. He decided to have the cats removed after the initial CAI, Borla, Diablo tune because he wanted to see how much louder the exhaust would be and had planned to do headers anyway. After the cat removal, the truck started running very weakly and the check engine light was on which we expected with no cats. He liked the exhaust note so he decided he wanted to go ahead with the headers. We installed the headers, removed the rear O2's and installed new OEM O2's in the headers. After the header install, the truck was still weak so we installed the stock tune. The check engine light never came on with the stock tune and it actually seemed to run a little better than the Diablo tune. We re-installed the Diablo tune, the light still never came on, but it runs no better than the stock tune.

The only change from running great to running poorly was the cat removal and now header installation which didn't change anything performance wise over the cat removal. Could it be in some kind of reduced power mode, but not kicking a code?

I do know the intake gaskets are leaking a little, but they were leaking a little when it was running great as well. I will be replacing them in a couple of days.

Thanks,

[jackd]

I had a chance to drive the truck for a little while this afternoon. It did finally set the codes for the missing rear O2 sensors, but nothing else.

[mikel]

tough to say, just gutting cats really shouldn't change the way the truck runs IMO.

Custom tune is needed for sure.

Thanks

[jackd]

tough to say, just gutting cats really shouldn't change the way the truck runs IMO.

Custom tune is needed for sure.

Thanks

It seemed odd to me as well, but that is the only thing that changed the day the truck began running poorly. I guess custom tuning is the only way to find out.