I knew that there was a crack in my exhaust manifold on my '99 3ZR; actually I knew to look for it thanks to all the posts I read on TW. There has been a noticeable: loss of power, drop in MPG, increase in noise - and I don't mean a good sound either. I haven't smelled any exhaust leaks in the cab or gotten any CELs, but it seemed that the crack has steadily been getting worse. Or as ******* Toyota diagnosed it, "a leaky exhaust gasket."
My suspicions were confirmed when I took this picture (finally removed that oddly complicated air intake system):
I had been waiting for the group buy on the Doug Thorleys, but I didn't know when that was going to come together, so I went ahead and got the factory kit from Nix 99 in WA. FYI, it took 4 days to Chicago. Obviously not quite as nice as a set of SS long tubes, but looks better than the stock cast piece:
So I pulled the stock part off yesterday, which ended up being a little more of a pain than I figured. Of course, if I had to do it again, I could definitely knock it out in an hour or so. Anyway, I pulled the stock piece off and noticed that the cracks (plural!) were more serious than I thought, and went around the entire manifold. It was only a matter of time before the whole thing cracked completely.
A little deconstruction video here, demonstrating exactly how cracked the manifold was.
You can see by the profile shot just how bad the exhaust was leaking. Note the color of the metal; the dark areas obviously have been leaking exhaust.
So I installed the new part and hooked everything up. Before I reconnected the airbox though, I ran some TB cleaner through the air tube to clean out the TB. Apparently it hasn't been cleaned in quite a while. I backed the truck out of the garage a little bit and blew out quite a bit of white smoke. The alley looked like it was being fogged for mosquitoes.
I'm looking forward to checking the mpg over the next few fillups to see if the new manifold helps. I took the truck for a short spin, and the sound is much better. No more of that "leaky air compressor" sound. There seems to be a bit more of a low rumble, or maybe that's just how it should sound. The manifold has likely been cracked since I bought the truck last October, so I've never really heard a "good" exhaust sound from this truck anyway. At least the sound no longer detracts from the otherwise tough look of the stock truck.
I'm sure the header would sound better, but I didn't want to wait any more. And I doubt the extra couple hp I might get would make much of a difference in my life. The tach almost never sees over 2k anyway.