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Unread 09-15-2011, 01:45 PM   #1
medic-11
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1990 YJ Wrangler 
 
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Catalytic converter test pipe, diameter?

What size pipe would I need to buy to temporarily bypass my catalytic converter on my 1990 yj, with a 4.2? I am seriously only looking to test if my converter is getting plugged. thanks

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Unread 09-15-2011, 03:38 PM   #2
jeepinvader
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You should be able to tell if its bad just by shaking it. If it rattles, its bad. And you're not supposed to talk about illegal stuff on here. And bypassing the cat would be considered illegal.
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Unread 09-15-2011, 05:21 PM   #3
bigbossd1030
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Shaking it won't tell you if its plugged, that will tell you if the inside is broken. If its plugged the piece will be lodged. Why do you suspect its plgged. Take it off and have a look inside with a flash light.
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Unread 09-15-2011, 07:01 PM   #4
NonRubicon
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^This. I went to replace my muffler and discovered the cat was plugged. Big chunk of the catalyst broke off and wedged itself in the outlet, didn't rattle at all.

What symptoms make you think it is plugged?
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Unread 09-16-2011, 08:37 AM   #5
medic-11
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Some basics first;
1990 YJ, mostly stock, 4.2 liter, 5-speed Puegeot, 3:07 axles, 31" tires, no lift, engine runs great- doesnt leak a drop, doesnt use any oil, 120k original miles.

My Jeep starts and idles fine. Its been nuttered, and I still run the Carter factory carb. I can drive down the road with plenty of power, as long as I am under 55mph or not reving too high. No issues with power or torque whatsoever under ~2200 RPM. I can hit ~3800-4000 RPM briefly like in first or second gear with decent power. The redline for my engine seems to be about 400 rpm, according to the factory tach. Its not that it wont rev higher, it just doesnt like to or seem to make any power at or over 4k. On the highway, I can hit 65 easily, but not much over no matter how hard I try. In 4th, 65 is around 2500 RPM, and I run out of power to go faster. In fifth I am only at ~2000 RPM and its not turning fast enough to make power to remain at 65 or above.

I do understand that aerodynamically- Its much harder to achieve higher speeds in a wrangler. One thing I notice is that if I run it hard- like accelerate hard to ~60, or if I drive much over 60 for any period of time, I get an awful smell from the exhaust. I can also drive anywhere (winter/summer it doesnt matter) and not run any hotter than ~210 according to the factory gauge BUT If I am on the highway, A/C off, it will hit well over that anytime I try to drive over 65 for any period of time.

Im thinking the smell is the converter getting hot. The restriction may be causing my higher engine temps when the converter is expected to flow any more than ~2200 rpm for any period of time.
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Unread 09-16-2011, 09:00 AM   #6
ssyj94
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It should be 2.25" tubing with the symptons it sounds like the cat could be bad.
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Unread 09-16-2011, 04:04 PM   #7
nembudonna
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You can just cut the pipe before it goes into the cat,(because the mourons welded it) and run it open and see if works. Then if that's not it you can just put a coupler on it with a couple of clamps. It sounds like that's it though. Can I be arrested for this? I'am calling my lawyer.
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Unread 09-16-2011, 08:45 PM   #8
NonRubicon
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You mention that you run out of power near 4K. I think that is acceptible for the 4.2L, seeing as it peaks with 112 hp @ 3200 rpm, and 210 ft-lb torque @ 2000 rpm. I had to do the Team Rush upgrade to be able to reach 4k. Even then, with a good cat, the engine couldn't go above it.

3.07's and 31" tires? I have 3.55's and 31" tires and I will lose speed in 5th if there is enough incline or simply enough headwind, basically 5th is useless to maintain 65 MPH unless I'm on a flat road or going downhill. Your gearing may simply be too tall, you might be dumping too much unburned fuel into the exhaust trying to keep up speed by going a little heavier on the throttle. Excess fuel in the exhaust can overheat the cat, and trash it.
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Unread 09-17-2011, 08:42 AM   #9
bigbossd1030
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^^^
I agree 4k would be hard to reach with any amount of power. I would still check your cat, but if its plugged, don't expect anything above 40 mph or 30kmh. I think you are expecting too much from a jeep, its speed isn't its strong point. If you hit 110kmh or 65 and keep around 2500 Id say that's normal, well that's what I get at least.
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