cat temp is cooler coming out then going in - Third Generation F-Body Message Boards

koolcutta · 09-07-2009, 06:18 PM

I failed smog and is trying to figure out if my cats are dead I put an infrared thermometer on them and had 350F going in and 212F coming out. the car is a 91 5.7 with dual cats and both read the same hotter exhaust going in then coming out. From what I've read i believe the readings should be the opposite hotter exhaust coming out then going in. Can someone confirm this before i purchase new cats live in cali and we all cali cats are not cheap.

Goldenbullet44 · 09-07-2009, 07:48 PM

were is the thermometer located at the back?

koolcutta · 09-07-2009, 08:06 PM

Quote:

Originally Posted by Goldenbullet44

were is the thermometer located at the back?

the car is on ramps so i have the thermometer 2" from the cats entrance and exiting slip coupling. Also the car is fully warmed up when i'm taking these temps. The temp at the muffler is around 110F. So far I have 300F right before cat,200F right after cat and 100F at the muffler.

koolcutta · 09-09-2009, 01:01 AM

Okay so since its a know fact that cats gets really hot, glowing red hot when they have a really rich mixture whats the easiest way to make a L98 run rich.
1 disconnect map sensor
2 disconnect spark plug wire
3 other suggestions

my logic is if the cats don't get hot they aren't working

gurkgurkgurk · 09-09-2009, 02:54 AM

i always thought that the exhaust after the cat would be less hotter than the exhaust going in. just thinking logically since the air would help cool the exhaust tubing. not to mention the AIR system pumping air into the cat via that little tube.

but as far as figuring out why your car doesnt pass smog. id just post up your sheet with all your data on the dyno run.