Catalytic Converter Removal

[Doug345]

Sup All,

I just bought a Megan Racing Decat Pipe (with bung for temp sensor) for my '94 R32 GTR but before installing it I started doing some research:

I see alot of people saying to just cut the temp sensor and the engine light will not come on. Some people say once cutting the sensor though, the light comes on. I need some feedback on this for this reason: my temp sensor is a bi**h to remove lol. 14mm is too big. 13mm is too small. 9/16" is too big. 1/2" is too small. Adjustable wrench will not grip...wtf right?

Next: say I do get the sensor removed from the stock cat, will putting it into the bung of the decat get high readings leading to an engine light anyway seeing as the internals of the cat will no longer be present, and temperatures will ultimately be higher? If this is the case, should I just tie strap the sensor to the underside of the car with some protective covering over the end? I would like to avoid cutting it for the reason that I live in the Cayman Islands where there are absolutely no emission tests but if I wanted to move to Canada (or anywhere else) and bring my GTR, I would need to keep the stock cat and sensor for passing emission standards there.

Lastly: The 14mm bolts that attach my cat to the cat-back system are not budging. Any tips/suggestions to get these off without cutting the flange? I tried using WD40 to loosen them but nothing. Maybe LiquidWrench? CorrosionX? Like I said, I want to be able to put the cat back on if I were to move to a place where emission testing is present. The Megan Racing Decat does come with new bolts and nuts and gaskets, so if push comes to shove, i could cut the old bolts, but honestly, I'm not versed in welding/cutting torches (or dremels for that matter) so any feedback here would be much appreciated as well.

TL/DR: I want to be able to replace my cat with a decat with the option of replacing the cat in the future. Odd sized nut. Seized nuts. Any engine light issues?

[rob_96]

my sensor has been removed and my engine lights comes on its very annoying, i want to find one and reinstall it

[MB38]

I just went through this a few days ago on my R32.

I tried everything in my power to get the EGT probe out of the old cat. No luck. I finally mangled it so badly using vice grips that I decided to cut the cable, cap it off, and see what happened. No warning lights for me yet. I wish I hadn't had to cut it, but that was the scenario I found myself in.

Regarding the bolts, just spray them with some PB Blaster, have a cup of coffee, then give 'em a go. Try a breaker bar [assuming you can get enough clearance under your car] or an impact gun. You should be able to pick up some fancy new bolts at your local hardware store. Just use some anti-seize on them to keep them from locking up on you again.

[ck_chino]

For me the most effective way is with a torch. heat it up at the base and use vise-grips.

[Skym]

The cat over heat sensor is plugged in under the front passenger seat.

If you put your hand under the back of the front passenger seat, there is a plug. Some remove the front passenger seat to access this plug.

If unplug the cat overheat sensor it should fit through the rubber bung in the floor pan. Then can remove the cat overheat sensor later on from the cat.

All that cat overheat sensor does is set off the cat overheat light on the dash when the cat overheats (around over 800 degrees C with exhaust temps). This means take it to Nissan dealership to get it fixed / replaced. From what I can remember, it says that in Japanese on the backside of the drivers side sunvisor.

Some say it activates something on the ECU (run richer, etc), but have yet to see evidence of this.

This cat overheat light on the dash also acts as a engine check light for when checking for error codes on ECU (goes off if ECU is set in diagnostic mode via screw on side of engine ECU).

If want to turn the cat overheat light off you can unplug and earth at the plug under the drivers side passenger seat (neat removal, ask a auto electrician on how to do this properly).

Or clamp the cat overheat sensor to the side of exhaust / cat elimination pipe with a intake hose clamp (this is how I have done it on my car). This earths the sensor which turns off the cat overheat warning light on the dash.

[Doug345]

Thanks everyone for the feedback. Will update in a bit to say how it goes

[PurpleStreak]

I managed to get my sensor out by getting a wrench on the sensor and putting an adjustable wrench on the exhaust flange for maximum torque. Oddly I couldnt get the plug out of the Megan test pipe lol. So the sensor is sitting in the frame rail right now; no light.

[Skym]

You're welcome. As long as the cat overheat sensor is touching the exhaust or chassis it is earthed. Some cut the cat overheat sensor off and earth the wiring to the exhaust shielding on the chassis, just above the cat, etc. It is a sensor that can be replaced via a new sensor from Nissan.

[caliber676]

Use a acetylene torch and heat the nuts/bolts until they are red hot then crack them loose. Repeat until they come off. There isn't going to be a penetrating spray good enough to take off a fully seized exhaust nut, they'll just strip before they budge. Remember to use a 6pt socket too, if the rust makes it hard to fit the right size, hammer the socket on.

[Doug345]

UPDATE:

Happy to report that I got the cat-back exhaust flange nuts off with liquid wrench yesterday. Once I did this, I disconnected the sensor underneath the seat as per Skym's instruction (didn't have to remove the seat). Turned the car on and no light comes on. After that it was as easy as feeding the wire through the hole in the floor and removing the cat and sensor all in one go!

Unfortunately, the nuts and bolts that Megan Racing supply with their decat are too big for the stock Y-pipe so I had to wait until today to buy some slightly smaller nuts and bolts. Should be able to mount up the decat when I get home today and I'm just going to leave the plug in the decat bung.

[Skym]

Strange, it should set of the warning light on the dash. Most sensors do that when unplugged. It could be that they removed the warning light bulb in the dash.

[Nismo_line]

I had this same problem and had to cut the sensor. When i uplugged it there was no light but after getting the car back on the road and driving for two weeks it felt like it was running way rich. This is a new motor and needs a tune but I tried plugging the sensor back in and so far it seems like its running better. Could just be me but I thought it was worth a shot