OK, so I just seafoamed my engine. While the bottle was emptying, I was already noticing some smoke billowing up around the exhaust manifold. Seems that there is an exhaust leak around the manifold flange/downpipe joint. Is this something I should be concerned about, and could it be causing my computer to think the o2 sensor right below that is going bad? As always, thanks in advance for all the help.

 

i had the same issue sounded like a diesal with a 5" exhaust but no check engine light came on

 

Mine doesn't stay on all the time, but lately, anytime I take it on an extended drive, it comes on. Oddly enough, it comes on during the return trip. Three times in the last 3 weeks, nothing on the way there, but about half way back, DING x 3. Comes back o2 sensor every time.

 

depending on the code, yes your leak will alow fresh 02 to be drawn into the exhaust and read by the 02 sensor. my guess its reading lean due to high oxygen and dumping more fuel to compensate.

 

Yep, it's been reading lean in that bank. Guess it's time to replace the manifold gasket. Is this something I can fab, or am I gonna have to order the exact part from AB?

 

those gaskets would be very tough to make if you could even find the material that would take the heat, im sure they are cheap. soak the nuts with pb blaster overnight and give em a little whack just before you try to break them loose. this should aid in not breaking to stud off when you are repairing the gasket.