4Runner4Christ

Can someone help me understand the stock exhaust setup on my Runner? I have a 1999 4WD with the 3.4L engine. I crawled under there and this is what I have front to back: The pipe comes off the exhaust manifold, there is a section of pipe with a sensor in it, then something with a heat shield around it, another section of pipe, then another thing with a heat shield (which rusted off a while ago), then another section of pipe with a sensor in it, then the muffler. What I really want to know is what are those two bulbous things with the heat shields? Are they both catalytic converters, or is there just one cat and one other thing that I dont know what it does?
Thanks for helping me understand what I got. I need to replace the cat and I am going to replace the muffler while I am at it (probably something aftermarket like a Magnaflow/Carsound setup).

kevin444

Yup those 2 small buldges with heatshields are Cats. And the final big buldge is the muffler.

4Runner4Christ

Thanks Kevin. Now, as I look into aftermarket solutions I need to know what size inlet/outlet pipes I will need. Are they 2 1/4" or 2 1/2"? Thanks again.

kevin444

Id match whatever the flange's diameter are for the headers. Should be 2.25. I wouldnt go 2.50 if the headers arent otherwise your going to lose torque in the low end rpm band. But gain in the high end rpm band.

4Runner4Christ

Thanks Kevin.

x-elite

I've been wondering if its Legal to run just one cat and a straight pipe out of there. I've got the pipe and welder to do it, Just don't if you can run manifold, cat, then pipe legally.

kevin444

Well if your in california probally wont pass. If you live in another state you might be to get away. Why dont you just have it flanged?. So bolt on when smog check time comes along and bolt it off and bolt on a straight down pipe when your done with the smog test.

4Runner4Christ

This leads nicely into my next question... Other than the California thing (which is not an issue here), does anyone see a problem with going from a two cat exhaust system to one? If it is not a problem will I want to retain both O2 sensors in the system? Currently there is a sensor in front of the first cat and after the second cat. I am thinking: replace the pipe that comes down from the manifold which contains the first cat, run a pipe all the way until just before where the second sensor is, then while I am at it install a Magnaflow. What do you think of that setup? Thanks a lot.

kevin444

i myself actually posted that question when i still had a magnaflow cat. But since i live in california i figure i wouldnt risk it. SO i sold the high flow cat.

rimpainter.com

On a heavy 4WD vehicle you definitely want to retain back pressure, so a cat is a must. Also, tampering with a functional cat is a federal offense, so I would just avoid removing either cat (sounds like you have two) all together.

Your best bet is to go with headers to the stock cat(s), hack out the stock muffler, and weld in a magnaflow or similar.

Right now I am actually contemplating a 14" magnaflow dumping just in front of the passenger rear tire. Less bends = better flow. However, mounting exhaust in front of the axle on a 4-door vehicle is illegal, so I don't know what I want to do. No matter what, I am getting a loud 14" magnaflow.

4Runner4Christ

[QUOTE=<96 Runner>]Also, tampering with a functional cat is a federal offense, so I would just avoid removing either cat...QUOTE]

I'm OK. I have a check engine light pointing to a code that calls for a replacement of the cats. I'll post my question again so you dont have to scroll up:

Does anyone see a problem with going from a two cat exhaust system to one? If it is not a problem will I want to retain both O2 sensors in the system? Currently there is a sensor in front of the first cat and after the second cat. I am thinking: replace the pipe that comes down from the manifold which contains the first cat, run a pipe all the way until just before where the second sensor is, then while I am at it install a Magnaflow. What do you think of that setup? Thanks a lot.

kevin444

I think its to comply with year 2000 emmision standards it just keeps on getting stricter. Just leave it. Or call magnaflow they have cats that will only pass federal and not california. SO either go with 2 hi flow cats or stick with the stock.

alltrac165

As far as I know, you can replace two cats with one three way cat. Magnaflow offers federal and CA cats. The CA cat is twice as much, naturally, and has to do tighter construction standards. You will definitely want to keep your second O2 sensor, the ecu will throw a code if it's not there. It monitors what the cat is doing which is how you got the MIL to begin with. You'll have to check with the local smog station on whether or not it's ok to use just one replacement. If you can use just one, I would put the new cat in right after the first O2 sensor, move the second sensor to right behind the cat, then pipe to the muffler. It's best to keep the sensors and cat as close to the engine as possible for best operation. I'm running a 24" Magnaflow muffler and the CA cat, and it works great for me. Still has some authority, but isn't obnoxiously loud. But I like to be subtle, so ymmv.