Ok so I replaced my exhaust manifold with a new oem. Now it's misfiring. I checked to make sure plug wires are all on tight. I find it hard to believe that it's a coincidence that it could be plugs or wires. The manifold sounds like it might have a leak could that be the issue.

 

Ok so I've determined that my new manifold is not leaking. But it seems that all of bank one is not firing properly. So unplugged each coil one by one to see if it changed engine idol on bank one. No change in all cylinders bank one. So I tried bank two one by one. Each cylinder made huge difference in idol on bank two. Dose anyone have any ideals?

 

What have you found so far? anything new? I have an 04 Burban with rough running and misfiring and I am at a loss.

 

Ok so my problem was from my cat being clogged. I clogged it during the removal of manifold. I had to use saws all to cut bolts at what would be the collector connection. The violent banging from saws all broke apart the inside of cat. I ran it with just manifold to determine that it was the cat clogged. I cut cat off and punched it out and welded it back on and deleted down stream cat sensors. Hope this helps

 

Without the after cat O2 sensor, the ECM will be messed up as far as getting the correct fuel mixture.

 

Not if he was able to do the delete correctly in a way that allowed that sensor to bypass. And the upstream sensor is your fuel mixture. i'm not 100% as to what the downstream does.

 

As I understand it the purpose of the downstream sensor is to make sure the catalyst is doing its job, basically an emissions function...

 

Lets do away with emissions like in the old days

We would get better fuel mileage, more power, and better sound... I miss the old days, its nice to look at a 64 Thunderbird, a 66 Mustang, and two boats with 351W's and see no cats

 

as far as I know the upstream O2 dose the monitoring of the fuel mixture. down stream only makes sure that cat are working correctly. Im not throwing any lean on bank (1)(2) codes like it was before.

 

Old days? my 5.7L tahoe barely made 150 HP.

my 2009 5.3L makes over 300.

i'm not sure you remember the old days correctly...