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2000 GXE, 150k miles
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23 Posts
Discussion Starter #1
I have a 2000 Altima with a clogged up pre-cat. What will happen if I drive it after completely removing the downstream (bottom) o2 sensor? I ask because my uncle is going to hollow out the pre-cat for me but he lives an hour away. So I am going to get him to remove the bottom o2 sensor too so that I can take it home and modify it (to keep the CEL off), then drive it back to him so he can put it back on. I just want to make sure it will be ok to drive without the sensor for those 2 hours.

Thanks
 

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1,201 Posts
OK but if you leave a hole it will make noise. It's the front one that is important to basic engine running.
 

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09 Altima 3.5SE 6MT Sedan
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5,737 Posts
Why bother modifying it? Just show up with a pair of sparkplug antifoulers, drill 'em out, stack'em, thread them on the end of the lower O2 sensor...and reinstall after gutting the precat.

If you must remove it, buy a cheap sparkplug with the same threading and install in place to seal off the hot gases that could melt harness wiring and other engine plastic, reduce your exhaust backpressure, make annoying noise etc etc.

It will run, probably rougher than before, won't damage the inside of your engine, but could wreak merry havoc on stuff around the hole (keep in mind the temp of exhaust gas, the increase from any precat activity, then funnel and focus that under pressure for 2hrs....)
 

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2000 GXE, 150k miles
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23 Posts
Discussion Starter #4
Ok thanks for telling me that. I'm pretty sure there is no room for foulers on these models though. The OE sensor is easy to modify on these, all you have to do is solder a 1.2 ohm (or close) watt resistor on the black ground wire and you're good to go, unlike some other sensors you have to cross wire them and what not. So it looks like I'll just have to have him put on a new aftermarket cat. Otherwise I'd have to buy a new OE sensor for $150, modify it and bring it to him but that would cost the price of the new cat. I don't have the tools and equipment to get under the car to get the old one off thats why he has to do it.
 

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09 Altima 3.5SE 6MT Sedan
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5,737 Posts
You better confirm your resistor mod works...as I've never heard of anyone having anything close to that easy a ride defeating emissions systems. If you don't have clearance, you can get 90' bung extenders on eBay.

Update...here's the thread he's referring to on the resistor mod

http://www.nissanclub.com/forums/f-q-1993-2001/144963-p0420-fix.html

(and I forgot this was a 2000 Altima....this won't work on Gen3 or later)
 

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09 Altima 3.5SE 6MT Sedan
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5,737 Posts
I know the antifoulers work, they are robust and about a simple as simple can get. The resistor may work....however given your two hour round trip...I'd want a 'one and done' type solution.

Besides, around here the soldered resistor would last probably for 2-3 weeks of winter before succumbing to salt, slush and vibration.
 

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2000 GXE, 150k miles
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23 Posts
Discussion Starter #8 (Edited)
I know the antifoulers work, they are robust and about a simple as simple can get. The resistor may work....however given your two hour round trip...I'd want a 'one and done' type solution.

Besides, around here the soldered resistor would last probably for 2-3 weeks of winter before succumbing to salt, slush and vibration.
Problem for me is the antifoulers will get me in trouble at emissions. So I guess what I'll do is find something that goes around the wires that will hopefully protect the resistor and hide it at the same time (I don't live in Cali so I'll still pass just fine with only the smog cat). And I just checked and my parts store has a fitted sensor in stock, so I'll ask to look at it and find a spark plug that matches the threads.

Thanks for all the help, I'll update y'all to confirm if it works for sure.
 

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2000 GXE, 150k miles
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23 Posts
Discussion Starter #9 (Edited)
Alright this is a very late update but I just drilled out the precat and I started having problems after 45 minutes of driving. I drilled it out from the bottom without taking it off the manifold because it was seized and impossible to remove. I'm concerned that maybe some catalyst got inside of the engine or something because it started acting funny, the CEL came on and I stopped at autozone which the code read P0171 (system too lean). When I was drilling it out there was dust flying everywhere and the whole engine compartment is covered in catalyst even though I drilled it out from the bottom. Do ya'll think it could have got up in the engine? I looked in the cat really good and got all of it out that I could see and put a vacuum hose over the hole for a few seconds afterwards.
 

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If that was a ceramic type cat brick there you just spread the equivalent of ground glass dust all through your engine............
 

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09 Altima 3.5SE 6MT Sedan
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5,737 Posts
Could be you just plugged up your already dirty air filter. Hose the engine down well to wash away or bind any loose dust. Open and inspect your airfilter...if you cannot see light through the pleats, it's more than done.
 

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2000 GXE, 150k miles
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23 Posts
Discussion Starter #12 (Edited)
If that was a ceramic type cat brick there you just spread the equivalent of ground glass dust all through your engine............
It was the original oem cat. And I hope you're joking, if not, what should I do???


Could be you just plugged up your already dirty air filter. Hose the engine down well to wash away or bind any loose dust. Open and inspect your airfilter...if you cannot see light through the pleats, it's more than done.
I'll check it, but the P0171 code means that the engine is getting too much air, so I don't think this would be the problem
 

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09 Altima 3.5SE 6MT Sedan
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5,737 Posts
He's not joking, cat dust is bad stuff, for you and your engine.

You are right on the too lean, my bad...that makes me think now maybe you clogged up your A/F upstream sensor with some of the dust cloud you apparently created. Maybe pull the upstream sensor and inspect for dust etc? Maybe wash it out a couple of times with methanol or similar?
 

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2000 GXE, 150k miles
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23 Posts
Discussion Starter #14 (Edited)
If it got inside of the engine am I screwed? What can I do?

I just read that a cause of a P0171 code can be contaminated oil
 

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2000 GXE, 150k miles
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23 Posts
Discussion Starter #15 (Edited)
And just a reminder that this is a 2nd gen Altima, not a 3rd gen that has the valve that allows the catalyst to be sucked back into the engine when running. (Don't know if that makes any difference in my situation)
 
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