1991 Camaro RS V6 T5

Just thought I would share this with you guys:

Prior to my first emissions test, I changed plugs, wires, cap, rotor, fuel filter, air filter and ran seafoam through the tank. Exhaust was very stinky when I first obtained the car, prior to replacing the above items and was stinky afterwards as well.

Emissions results:
Hydrocarbons: 1,087 (220 allowed) Carbon Monoxide: 2.31 (1.20 allowed)

I was receiving a check engine light, so went towards the next avenue - O2 sensor. The pigtail was severed with frayed copper wiring sticking out. It was also ridiculously hard to remove. The old sensor was caked with carbon beyond recognition. Replaced the O2 sensor and spliced in a new section of wire. I still received a check engine light but thanks to this board, found out to obtain ECM codes...used a jumper wire on pins 5 & 6 of the OBD connector and received code 32.

Removed the EGR and started up car to check if exhaust was plugged...it blew exhaust out the top. Next, I unbolted the EGR steel hose entering the throttle body and the hole seemed narrow and caked with carbon...used a coat hanger wire and a tiny amount of carburetor cleaner inside. Still received the check engine light so the next solution is a new catalytic convertor.

Took the car in to the exhaust shop yesterday and watched them remove the old cat; it was completely hollowed out as expected. The muffler was also a cheap OEM replacement that the previous owner or previous-previous owner had installed long ago, all the fiberglass inside was completely wasted away. Went with Magnaflow on both cat and muffler.

As soon as they started it up, I could smell practically no exhaust fumes at all. Went through emissions and passed.

On a side note, since I have new exhaust installed, I noticed the shifter doesn't vibrate nearly as much while driving (not sure how that can be related but I'm not an expert).

 

Congrats on it being a "relatively" easy fix. Good lesson here for everyone, especially those who need to pass emissions. YES< the cat is required! lol

 

Actually I'm impressed on the diagnostics. You did the basic tuneup stuff before testing but failed and needed to find out why. Start with the most logical easy stuff. You never know, cleaning the EGR and tube or changing the O2 sensor might have fixed it. A new exhaust system probably wasn't cheap but you now passed emissions and the engine probably runs a lot better.

What were the emission results when it passed?

 

The new cat did 90% of the work for you. Almost nothing that came with a cat originally will pass a sniffer without one.

The one thing about a "hollowed out" factory cat is that they sound terrible, even with a muffler behind them. A hollow "rushing" kind of exhaust note. Worse inside the car than it is outside.

Glad you got it passed.

 

Thanks for the diagnostic praise; I'm trying to become a better jr. technician / hobbyist. This board has helped out so much. Even after replacing the O2 sensor, the check engine light was still going on at random times. Even after unplugging the EGR passage I still received the check engine light. I figured I would get the exhaust fixed instead of going through emissions and failing again....yeah, $437 for new cat, muffler, pipes and labor.

New Emissions Results:
Hydrocarbons: 33 (220 allowed) Carbon Monoxide: 00.00 (1.20 allowed)

What a major difference!

Side note: One thing that doesn't make sense about cats however - exactly a year ago, I owned a 1979 Firebird (base model). It had true dual exhaust and a Pontiac 350 from a 1968 Firebird (traced back casting numbers). It also had 2 gutted catalytic convertors and smoked horribly from the driver's side pipe (did a timing and compression test and found cylinder #7 to be dead). Even oil was coming out of the driver's side exhaust pipe and it still passed emissions! I was waiting in line for 55 minutes while that poor exhaust pipe smoked the entire time. I still don't get it.

Regarding the old exhaust sound, yeah, it sounded kinda farty and such but not in a silly Honda way. Once they put on the new exhaust, it sounds like a baby V8, ha (low roaring sound).