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Old 01-16-2009, 09:18 AM   #1
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Awesome - cat failure

Cat went out on me, and the monkey who did exhaust work last time cut off the flanges, so it's a no go to hollow it out and trick the sensor (I'm broke right now).

On top of that, the pipes are so rusted I don't trust them for a cut/clamp repair at all, and the cat's basically right at the flex pipe. Oh, and the muffler's starting to fall apart. My gas millage has dropped like a rock and the car's a dog, so I know the cat has to be clogging upr or falling apart and blocking the pipe.

Well, today I'll be getting in some 2.25" mandrel bent piping, a 3 foot resonator, 4 feet of straight pipe, and a high flowing muffler in the mail. Next week I should get the new header, along with some flux core weld wire for the MIG and a cut-off disk to fit my miter saw for some clean fast cuts. On the 24rth I should have a new exhaust system from the header to the tail pipe and another mpg or more.

I'm going to try to dig up some sheet metal and make a nice box around the header to route a hot air intake to while I'm at it, which should help the warm up times considerably.

Up next on the list - address the slipping clutch. Gotta love spending money you don't have to fix the car that gets you to work.
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Old 01-16-2009, 09:47 AM   #2
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Hollowing out the cat won't trick the sensor. It'll keep throwing that emissions code if you don't put in a new one.

Or one of these.
http://www.o2simulator.com/index.php...5b609b73855bd7

Remember that these are for off-road use only. If you decide to bypass having a cat, you are doing so at your own risk. Don't come crying here if you get a fine for it just because you happened to get the link from here.

You've been warned.
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Old 01-16-2009, 11:13 AM   #3
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The rear O2 sensor works of off switching voltages in the millivolt range based off of temperature differences. At cold start, the front and rear O2 sensors are pretty close to each other. Once the cat reaches about 600*F, the rear O2 levels out a bit and reads totally different from the front O2.

If you pull the rear O2 out of the primary stream, it will effectively trick the computer - all for the cost of a $4 pack of non-foulers and a 1/2" drill bit. I know how the OBD 2 system works well enough to keep myself out of trouble - sometimes It's a pretty common trick for people that put in high flow cats or test pipes or gut the cat.

Either way, the cat is basically welded with 1/2" of pipe between it and the braiding on the flex pipe. There's no rear flange. I'm not going to cut at the rear of the cat, gut it, and run into piping that's so thin that it starts to crumble when I go to brush the rust off to re-weld it. I don't do exhaust clamps.
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Old 01-16-2009, 12:02 PM   #4
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Not all OBD2 systems are exactly the same. Some of them will throw a code if the rear O2 sensor doesn't change under certain conditions, the Tracker was programmed to do that.

If the rear O2 sensor didn't at least swing rich within ~5-7 seconds of fuel enrichment mode it assumed that sensor was bad, it didn't have to stay there it just had to read it momentarily. Usually that sensor would make the switch within 2-3 seconds though according to my data logging. Even under normal cruise, however, that sensor wouldn't constantly read the same level, there was always some fluctuation in the stream.

That ECU did a bunch of interesting little things. Under decel it would test the EGR system by activating it and reading if the manifold pressure increased via MAP sensor. This was the only use for the map sensor other than a back-up for if the air flow meter failed and needed to limp you home using the speed-density formula.
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Old 01-16-2009, 10:33 PM   #5
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Agreed - I've been fiddling on these cars from maintenance to turbocharging them and autocrossing them for a few years and have learned some tricks and oddities along the way.

There's a cat going on it either way, it just showed up today. Just waiting for my header to show up on wednesday right now.

The piping is going to be about 1/4" bigger in diameter, with mandrel bend angles instead of crush bent. A magnaflow high flow cat is going to be welded in there, along with a dynomax super turbo and a looong resonator with a clean simple stainless steel exhaust. I'll be welding in an O2 bung to make it all happy.
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Old 01-22-2009, 05:39 AM   #6
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Old 01-22-2009, 08:57 AM   #7
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aaaaahahahahaha
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Old 01-22-2009, 06:57 PM   #8
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Quote:
Originally Posted by zero_gravity View Post

A pre-hollowed out cat with the flange still in place...definitely for off-road use only!

Right up there with fixing cars with money you don't have is fixing cats with money you don't have...been there and done that too...
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Old 01-23-2009, 04:54 AM   #9
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Haha!

Thankfully all I have left to do is get a 2.0-2.25 adapter and I'm set. I'll be making an O2 bung at work today. Chop saw's running, sawzall's got new blades, cut off tool has new disks, the welder has new wire and tips, flanges on the header have been trued.

After work and the part time job, I should have this thing tacked and routed by 10, and welded by midnight.
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Old 01-23-2009, 10:59 PM   #10
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Somehow, some way, that is far beyond my level of comprehension, the gentleman that I let borrow my welder screwed up my 40 foot power cord extension - 220V - bad enough that there was a bunch of wire exposed. I didn't notice this until tonight, and it's a darn good thing I saw that long before I plugged it in and gave it a whirl.

The header installation went smoothly, the cat is welded to the flexpipe, the resonator's on, and I'm fabricating the over-the-rear-suspension pipe.

I started at 8:30PM, took a 10 minute break, spent an hour rewiring my welder, got a phone call from a long lost friend, and called it quits at about 2AM. 5 hours invested so far, and no burn through on the piping either (including the butt joints). I should have this finished by 10AM, including fixing any possible exhaust leaks that may or may not be present. It'll be nice to have my car running again, let alone running better than before.
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