1999 Cat Removal

**PGP1999** · 04-03-2017

I have a 1999 Grand Prix with 3.1L. Recently the flange after the catalytic converter rusted through and disconnected the exhaust pipe from the cat. I want to know if I can remove the catalytic converter completely and replace it with just a piece of straight pipe. Will the car run okay? Would I need to do anything special with the O2 sensor that is inline after the cat?

Any tips would be super. I live in a state without emission inspections or emission requirements. Thank you all.

MODS: I may have put this thread in the wrong category. Please feel free to move it if it is. Thanks.

**GTPpower** · 04-03-2017

You'll get a check engine light, but it will run fine. You can just take the rear o2 sensor and remove it. Cut the pigtail off so it doesn't drag, or zip tie it up.

**PGP1999** · 04-03-2017

Great, thanks for the reply GTPpower. Do they make an O2 sensor delete plug for the 3.1L like they do the 3.8L?

**GTPpower** · 04-03-2017

To my knowledge, all gm o2 sensors are the same size, so yes, any plug should work.

**Slick2500** · 04-04-2017

Just get 2 spark plug non foulers put them together, drill one out so the o2 sensor fits in it and install back in the hole. No CEL no need to spend $50 on the dummy plug thing.
http://www.nairaland.com/1180238/how...k-engine-light

**PGP1999** · 04-04-2017

Slick2500 - I suppose I worded it incorrectly, but that's exactly what I was looking for. I didn't want to eliminate the sensor, just prevent the CEL, but couldn't think of the name of that device. Thanks y'all.

**Slick2500** · 04-04-2017

Originally Posted by PGP1999

Slick2500 - I suppose I worded it incorrectly, but that's exactly what I was looking for. I didn't want to eliminate the sensor, just prevent the CEL, but couldn't think of the name of that device. Thanks y'all.

The spark plug non fouler or the dummy plug thing?

**PGP1999** · 04-05-2017

The spark plug non-fouler. I cut the cat out and put in about 30" of straight pipe. I ordered an O2 sensor bung (M18x1.5) from eBay. That should be here in a few days and then I'll weld in that bung and use the 42009 spark plug non-fouler. The car is still a little louder that I expected, but the muffler could be bad and/or maybe the exhaust manifold gasket is damaged or manifold may have been pulled away from the mounting surface when it was supporting the weight of the cat after the flange broke. I drove it around a little while after I removed the O2 sensor and cat, however I don't know if it activated a DTC yet because the CEL is already on from an EGR fault.

**SaukRapids** · 04-05-2017

Originally Posted by PGP1999

I cut the cat out and put in about 30" of straight pipe. The car is still a little louder that I expected, but the muffler could be bad.

Your mufflers are probably fine. Lol.

**PGP1999** · 04-05-2017

Originally Posted by SaukRapids

Your mufflers are probably fine. Lol.

I'd like to think so. I need to get her back in the garage so I can inspect it. Most of that car has rusted away (notably the driver and passenger rockers) so I wouldn't be too surprised if it had a hole or two in it. When I was driving it yesterday, the exhaust noise sounded like it was coming from the rear. Do you think removing the cat would make it noticeably louder? I did leave the resonator in place though.