# Catalitic converters **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [January 25, 2009, 8:23pm UTC](https://community.cartalk.com/t/catalitic-converters/25531 "2009-01-25T20:23:00Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![JayWene](https://avatars.discourse-cdn.com/v4/letter/j/8c91f0/32.png) [@JayWene](https://community.cartalk.com/u/JayWene)\ **Post date:** [January 25, 2009, 8:23pm UTC](https://community.cartalk.com/t/catalitic-converters/25531/1 "2009-01-25T20:23:00Z")
how do you know when your catalitic converter needs to be replaced? My MPG has dropped fron 42 down to 36 but I don’t think the car has lost power.I have changed the spark pluds and air filter but that has not helped.I have an 04 hyundai accent 4 cylinder standard trans with 222000 miles. I am not kidding ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [January 25, 2009, 8:26pm UTC](https://community.cartalk.com/t/catalitic-converters/25531/2 "2009-01-25T20:26:04Z")
Is the Check Engine light on? Tester ---
**Author:** ![hellokit](https://avatars.discourse-cdn.com/v4/letter/h/6a8cbe/32.png) [@hellokit](https://community.cartalk.com/u/hellokit)\ **Post date:** [January 25, 2009, 8:53pm UTC](https://community.cartalk.com/t/catalitic-converters/25531/3 "2009-01-25T20:53:10Z")
The engine is running rich. If there is a check engine light, the DTC (Diagostic Trouble Code) will give us a clue as to what may be causing the richness. Auto parts stores do a free code scan. Just ask. ---
**Author:** ![mcparadise](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mcparadise/32/32_2.png) [@mcparadise](https://community.cartalk.com/u/mcparadise)\ **Post date:** [January 25, 2009, 9:13pm UTC](https://community.cartalk.com/t/catalitic-converters/25531/4 "2009-01-25T21:13:59Z")
Don’t worry about the cat unless you have some indication it’s not working correctly. Reduced mileage is more likely caused by something else. I’d look very closely at the O2 sensor(s). I suggest having the car’s computer scanned for codes even if the check engine light is not on. ---
**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\ **Post date:** [January 25, 2009, 9:38pm UTC](https://community.cartalk.com/t/catalitic-converters/25531/5 "2009-01-25T21:38:18Z")
JMHO, but whenever the spark plugs come out a compression test should be run. This will verify whether or not the engine has any abnormal wear in the top end and which will in turn lower engine performance. Even a partially clogged cconverter can lead to loss of fuel mileage and the best method of checking for a converter problem is by using a vacuum gauge. It’s possible to have a partial clog, no CEL, and no apparent lack of performance. (About 6 months ago I ran across this on one of my cars; a SAAB. The car was running great, etc. but since I’m a tinkerer I put the vac. gauge on it one weekend and it showed a possible slight clog. The converter is easy to remove and I replaced it with a known good one out of my parts stash. Later I knocked some of the substrate out of the converter and a rough estimate showed that it had about a 30% clog in it.) ---
**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\ **Post date:** [January 25, 2009, 11:15pm UTC](https://community.cartalk.com/t/catalitic-converters/25531/6 "2009-01-25T23:15:09Z")
You could also lose mileage from: tire pressure, wheel alignment, over thick oil (watch out for quick lube places using the wrong viscosity), ignition timing and advance (if it has a distributor), sticky coolant thermostat, or a temp sensor that off but not enough to trip the engine light.