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Old 09-09-2011, 10:26 AM   #1 (permalink)
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4Runner 3.4 conversion...2 cats to 1

I have a 2nd gen 4Runner I am swapping an 01' California spec 3.4 auto into. The 01' 4Runner has 2 cats on it.

I am looking to replace both of them with one single cat. Has anyone had any luck with swapping 2 for a single?

I don't live in California so this is not violating any emission laws up here in Maine. I certainly want to run a cat but a single would definately make fitting it to the chassis a lot easier than having to run both.
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Old 09-09-2011, 09:59 PM   #2 (permalink)
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if you run a sensor bypass for the rear sensor, the ECU quits looking for the cat.
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Old 09-10-2011, 05:47 AM   #3 (permalink)
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I could do that but I have also read that the models that have an A/F sensor like mine, require the rear 02 sensor for calibration. URD stated that on there website.

Thoughts on that?
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Old 09-10-2011, 07:55 AM   #4 (permalink)
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personally i think its bullshit. if youre worried about it, get an A/F sensor calibrator. i would imagine they work better anyway.

to me it doesnt make sense that you use an archaic sensor to calibrate a hi tech one? right? the window in a regular O2 is very narrow. idk what good it would do an A/F meter.
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Old 09-10-2011, 11:28 AM   #5 (permalink)
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I absolutely agree. The question is when would it calibrate the A/F? It is behind the cat. I will try to do a little more research on this. I would love to run duals to behind the tcase (eliminating the crossover). Put the A/F sensor on one bank only, and then do one cat (just to be legal and it is the right thing to do, save the earth), and single exhaust out the back.
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Old 09-24-2011, 11:32 PM   #6 (permalink)
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I would think you would at least need a upstream o2 on each bank, and then maybe get away with one catalyst monitor after your one cat(or install both cat monitors behind your one cat). I don't know about toyota, but some of the other japanese manufacturers claim to use the cat monitor in their a/f corrections. Some also use the cat monitor to detect a failed upstream o2, as well as adjust a/f using the cat monitor if the upstream o2 is deemed failed.
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Old 09-25-2011, 08:31 AM   #7 (permalink)
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URD O2 simulator. Its about $100.
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Old 09-25-2011, 12:47 PM   #8 (permalink)
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Even though my Toyota training manuals state that the rear O2 in strictly for cat efficiency monitoring (along with numerous books), Toyota tech line has told me to replace the downstream O2 on a few occasions when you get a lean or rich code which negates all of the information I have been presented in the past.

Do you have experience with installing an O2 simulator on a Cali spec 3.4 with an A/F sensor?
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Old 09-26-2011, 06:06 PM   #9 (permalink)
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I have CA spec 3.4 tacoma. I installed a URD O2 sim. and it fixed my p0420 code. I still have both cats but they are shot. Loose material inside. I too am trying to figure out my next move. LC test pipe and eliminate them? I have heard bad things about losing needed backpressure.

I have no emisssions either. Only concern is performance. TTORA says it's bad but my friends truck runs well w/o cats. He has a code though.
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Old 09-26-2011, 06:55 PM   #10 (permalink)
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Quote:
Originally Posted by Wainiha View Post
I have CA spec 3.4 tacoma. I installed a URD O2 sim. and it fixed my p0420 code. I still have both cats but they are shot. Loose material inside. I too am trying to figure out my next move. LC test pipe and eliminate them? I have heard bad things about losing needed backpressure.

I have no emisssions either. Only concern is performance. TTORA says it's bad but my friends truck runs well w/o cats. He has a code though.
i run no cat, with 2.5 pipe. no issues at all.
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Old 09-26-2011, 07:20 PM   #11 (permalink)
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i run no cat, with 2.5 pipe. no issues at all.
no loss of low end torque? What about this idea of burning valves?
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Old 09-26-2011, 07:27 PM   #12 (permalink)
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no torque loss.
why would it burn valves to run no cat?
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Old 09-26-2011, 07:32 PM   #13 (permalink)
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I thought it sounded like bs but I have a lot to learn still. I don't know a valve gets burnt at all. Lean out?
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Old 09-27-2011, 11:25 AM   #14 (permalink)
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Well, LCE has no test pipe for me. It looks like a welding job. 86 those cats.
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Old 09-27-2011, 12:12 PM   #15 (permalink)
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ok well im a toyota tech . the front a\f raito sensor is needed. you dont have to use the rear o2 sensor. it is for cat. eff. motering only.

you dont have to run a cat. but please do and save our earth,
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Old 09-27-2011, 12:15 PM   #16 (permalink)
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Quote:
Originally Posted by Wainiha View Post
I have CA spec 3.4 tacoma. I installed a URD O2 sim. and it fixed my p0420 code. I still have both cats but they are shot. Loose material inside. I too am trying to figure out my next move. LC test pipe and eliminate them? I have heard bad things about losing needed backpressure.

I have no emisssions either. Only concern is performance. TTORA says it's bad but my friends truck runs well w/o cats. He has a code though.
Do you know what your long term fuel trim looks like with the O2 simulator (assuming you have access to a scanner)?

I don't you will have issues with burning valves. TTORA has many people blaming burnt valves on running no cats. First, why are so many people removing cats? Second, pretty much everyone in TTORA is running a 2.7 or a 3.4

The 2.7 is notorious for having exhaust valve issues. Therefore you have a large number of people complaining about it. Removing a cat will reduce backpressure (not by much with a modern converter so I don't buy that excuse) but reduced backpressure is not going to ruin a valve. Having no backpressure can ruin exhaust scavengning which can alter the way the engine runs. I think another contributing factor is when you reduce backpressure by alot (no cats, glasspack muffler, too big a diameter), you reduce the flow of EGR gasses which then cannot reduce combustion temps. EGR is designed to lower temps and reduce NOx emissions. If you remove any exhaust restriction, EGR does not flow and peak combustion temps climb. The 2.4/2.7 uses EGR and relies heavily on proper calibration of vacuum/pressure signals to work correctly.

So that would be my reasoning of why TTORA is saying they blows valves up when removing cats. That and TTORA also has a lot of dubs on its forum...
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Old 09-27-2011, 12:18 PM   #17 (permalink)
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ok well im a toyota tech . the front a\f raito sensor is needed. you dont have to use the rear o2 sensor. it is for cat. eff. motering only.

you dont have to run a cat. but please do and save our earth,
I have no issues with running a cat. I like my planet as well

The issue is can I get away with running an ordinary non-CA approved single cat on a Cali spec 3.4? I doubt it will fly with a single cat and using the post cat 02. If you run a single cat and an O2 simulator, would the ECM be happy?

Simply saying that the post O2 is for cat efficiency isn't enough because I have been told otherwise by corporate trainers and tech support. (I guess I answered my own question)
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Old 09-27-2011, 03:39 PM   #18 (permalink)
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Guess I'll do a 2 into 1 and still run the O2 sim. A non CA cat from Magnaflow I guess.

And I do care about polution. But w/o money options are slim.
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Old 09-27-2011, 07:54 PM   #19 (permalink)
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Quote:
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I have no issues with running a cat. I like my planet as well

The issue is can I get away with running an ordinary non-CA approved single cat on a Cali spec 3.4? I doubt it will fly with a single cat and using the post cat 02. If you run a single cat and an O2 simulator, would the ECM be happy?

Simply saying that the post O2 is for cat efficiency isn't enough because I have been told otherwise by corporate trainers and tech support. (I guess I answered my own question)
I run the URD O2 Simulator on a CalSpec 3.4L with a single "spun" Magnaflow cat. I honestly ran the O2 simulator prior to the build as well with no ill effects at all. I'm now supercharged with URD 7th injector kit. Still no issues at all. No codes, nothing.

I used to get a lean code P0171, but it ended up being a bad MAF. Replaced it and its been code free for six months.
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Old 09-27-2011, 08:59 PM   #20 (permalink)
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use this instead of the simulator. http://www.vfaq.com/mods/O2bypass.html

and pietro, i really think there is some kind of misinterpretation of the 2nd o2 monitoring the a/f sensor.

i just dont think its possible at all. there are just too many variables for it to work properly.

i mean what happens when your cat starts taking a shit and starts tricking the rear O2.
common sense says no way.
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Old 09-27-2011, 10:31 PM   #21 (permalink)
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I run the URD O2 Simulator on a CalSpec 3.4L with a single "spun" Magnaflow cat. I honestly ran the O2 simulator prior to the build as well with no ill effects at all. I'm now supercharged with URD 7th injector kit. Still no issues at all. No codes, nothing.

I used to get a lean code P0171, but it ended up being a bad MAF. Replaced it and its been code free for six months.
Weld in or did you use one of their bolt in appplications? If so which one the front or the rear?

Last edited by Wainiha; 09-27-2011 at 10:31 PM.
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Old 09-27-2011, 10:36 PM   #22 (permalink)
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Do you know what your long term fuel trim looks like with the O2 simulator (assuming you have access to a scanner)?

I don't you will have issues with burning valves. TTORA has many people blaming burnt valves on running no cats. First, why are so many people removing cats? Second, pretty much everyone in TTORA is running a 2.7 or a 3.4

The 2.7 is notorious for having exhaust valve issues. Therefore you have a large number of people complaining about it. Removing a cat will reduce backpressure (not by much with a modern converter so I don't buy that excuse) but reduced backpressure is not going to ruin a valve. Having no backpressure can ruin exhaust scavengning which can alter the way the engine runs. I think another contributing factor is when you reduce backpressure by alot (no cats, glasspack muffler, too big a diameter), you reduce the flow of EGR gasses which then cannot reduce combustion temps. EGR is designed to lower temps and reduce NOx emissions. If you remove any exhaust restriction, EGR does not flow and peak combustion temps climb. The 2.4/2.7 uses EGR and relies heavily on proper calibration of vacuum/pressure signals to work correctly.

So that would be my reasoning of why TTORA is saying they blows valves up when removing cats. That and TTORA also has a lot of dubs on its forum...
I have a lean code now. Now and in the past that always coincided with the long term fuel trim changing. 19.5 jumps to 39.5 and the 0170 code pops up. This both before and after the simulator. Right now I think a sensor is bad. The URD worked fine for a good while.
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Old 09-28-2011, 05:33 PM   #23 (permalink)
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Bump. Still looking for info and experience on this topic.
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Old 10-02-2011, 06:44 AM   #24 (permalink)
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Weld in or did you use one of their bolt in appplications? If so which one the front or the rear?
Are you asking about the cat?

Its just a single Magnaflow spun cat. Mounted between the two O2 sensors.

Most P0171 codes are thrown from a dirty or bad MAF. A lot of times its because of an open air cleaner allowing a lot more dirt into the compartment. I cleaned mine about 30 times before I said screw it and replaced it. Haven't thrown a code since.
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Old 10-02-2011, 02:56 PM   #25 (permalink)
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Yes I was talking about the cat. I was looking at Magnaflows bolt in. I was thinking if I bought the first one(as opposed to the 2nd) with the bend from the cross over, it be easier to weld in the rest of the pipe, because it's straight. One instead of two, as discussed. Thanks.
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