So here's a tutorial in 4Runner exhaust mods pieced together from research & experience.
Where || is a bolted connection, | clamped connection, and > is a flow within the same piece or pieces welded together.
OEM Configuration:
Engine || OEM Manifold > 1st O2 > 1st Cat || 2nd O2 > 2nd Cat > Y-pipe || Mid-pipe > Muffler || Tailpipe
Shorty Headers: || Shorties > 1st O2 > OEM 1st Cat ||
Long Tube Headers: || Headers > 1st O2 ||
Y-pipe: || 2nd O2 > Y-pipe ||
Cat-back Exhaust: || Mid-pipe | Muffler | Tailpipe
Aftermarket parts will replace sections between the bolted connections. Headers replace the OEM manifolds, Y-pipe for Y-pipe, and Cat-back for the Mid-pipe and further to the rear.
Shorty headers are usually the simplest option for headers. However, on the 4Runner and many other modern vehicles, the OEM Manifolds are integrated with the first catalytic converter. Which means to use most shorties, you would have to cut the 1st cat off of the manifold and either a) add a flange to connect to shorties or b) weld the OEM 1st cat onto the new shorties. This is a lot of work, and gives lots of chance for the alignment of the exhaust to be slightly off. Alternatively you could weld "straight pipe" without cats to reach the Y-pipe, but at that point you're better off to buy Long Tube Headers.
Long tube headers are a better option for power and installation, however, they completely remove the 1st cat from the truck. Because the first cat is between the two O2 sensors on each side, when the rear O2 sensor reading is the same as the front O2 sensor it will throw a CEL and code for the cat not working properly.
This is the issue that I've been having. Tuesday added code P0430 to the previous P0420. Gadget got tech support in touch with me and we're going to reprogram the UCON-EMS to account for this next week.
Another work-around for this is the O2 simulator, which feeds the ECU what it wants to see from the 2nd (or downstream) O2 sensors. While this will prevent a CEL and codes, it doesn't reprogram the ECU for the added exhaust capability hence you won't see the full potential of the headers which is what [MENTION=234088]spoonmectr[/MENTION] is getting at.
For those wondering the only difference in headers between 2010-2012 & 2013+ is the addition of the port for the Air Injection system on the header. Otherwise they should be the same.
[MENTION=78968]oljedi11950[/MENTION] The URD Y-pipe replaces the 2nd cat which are downstream of all the O2 sensors. Replacing the Y-pipe, even removing the 2nd cats, won't generate a code in any way. So the O2 Sim isn't required for a Y-pipe or cat-back swap. The biggest appeal of the URD y-pipe is relocating the section which crosses over from the driver's side. On the OEM it's flattened out pretty badly and supported with a smaller tube inside the flattened section, whereas the URD y-pipe crosses under the transmission at full diameter deleting that flow restriction.
Cat-back is also downstream of all the O2 sensors so shouldn't throw any codes replacing that either. The catch for the 4Runner is that almost all the aftermarket (URD excepted) are the same 2.5" diameter pipe as OEM.
[MENTION=255155]AStraughn1[/MENTION]
With a) shorties which have the OEM 1st cats welded to them
OR b) long tube headers with an O2 Simulator installed
you shouldn't receive any codes or CEL.
As for a code reader, just about any OBDII reader with write/erase capability should be able to reset any codes you receive. The one I'm using in this case is an inexpensive $20 reader from Ollie's, so if it's stolen from the truck it's no big loss. It is good enough to read and reset codes.
This will not fix the problem, just make the CEL go away. After an appropriate engine run time, the CEL will return since you never fixed the problem. That's exactly what I've been doing the past 2 weeks. I cleared the codes the first time they came up, but I didn't add the cats back into the system between the sensors or an O2 Sim.
So the CEL and codes came back. I cleared them again without changing anything and they've returned again. I could install an O2 Sim to prevent this code from returning, however, the UCON-EMS box that's plugged into the ECU has the ability to override the ECU for the CEL, ignoring certain codes. That's what tech support and I will be working on next week, with a laptop connected to the UCON-EMS.
Remember that a combustion engine is mostly a big air pump. More air in, means more air out. Changing the exhaust without adding a bigger intake will help it flow better, but you're not going to see full realization of the performance without changing both. Also if you're not telling the ECU that you made changes, you're not going to see the power the manufacturer claims. While the Toyota ECU isn't as of yet programmable, that doesn't mean you can't get around some of its limitations with black boxes like URD's UCON-EMS, or MAF Calibrator.
