1973 - 1979 F-100 & Larger F-Series TrucksDiscuss the Dentsides Ford Truck
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78 F150 California truck. How can I test if my cat is bad? Exhaust smells horrible.
Unless you have a precat and post cat o2 sensor with scan tool hooked to computer, you dont, so as far as I know you will need a gas sniffer. The cat can make that smell from a bad state of tune or bad fuel. Antifreeze makes a funky smell too, as it destroys the cat. Are you due a inspection or something? You can do a back pressure test if you feel like it is getting blocked up. Really no way to check for proper operation without measuring input and output gases though.
We would drill a hole in the cat, and weld it up after we were done.
If it is passing smog, the cat is working (according to Cali anyway) LOL
A bad smell means its converting unused fuel, or antifreeze, or oil using the catalyst process. Do you have a missfire, or a overly rich carb setting, or oil being burned.
No oil being burned, truck runs good except a slight mis at idle that I could never cure-new everything minus carb rebuild. Truck runs great. Muffler is oem and has a large hairline crack in it. Would the cat get overly hot if it was clogged?
1978 F250 Lariat 4x2
2008 Expedition Eddie Bauer 4x2
You can tell if it's plugged. Little to no exaust coming out the pipe.
There is also a test with a lazer thermometer. But it's not an exact science. You read the incoming exaust temp and compare it with outgoing exaust temp. The outgoing temp should be hotter on a good converter.
If the temp going out is within 20 degrees of the temp going into it, then it's bad. within 50 degrees it's worn, and 100 degrees is ideal. this is on a warmed up converter.
Failing all that, a smog shop should be able to do a pretest for you and give you your tailpipe emissions. Real high HC is a sign it may be a cat, or excessive fuel problem.
My cat went bad in my DD as it began to rattle. It sounded as if a heat shield under neath was coming lose. It didn't have any odd, or different smells that I noticed. I remember in the 70's when I worked at the Ford garage most all the cars smelled of sulfur, or rotten eggs when they were running.
Every so often we would take the latest and greatest models to the mall across town early in the morning, and they made sure we got them to their locations for diplay and din't want the sulfur or rotten egg smell in the mall anymore than necessary. Usually we took in LTD's, Thunderbirds, a few Fairmonts, and on occasion a Lariat packaged dent side.
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