How can you test the catalytic converters to see if they should be replaced. I'm getting the rotten egg smell off an on (more on than off these days). Ever since the dealership reprogrammed the PCM last January my gas mileage dropped from 17 to 14mpg. I took it back and they claimed there was no problem and 14 was normal (never mind the fact I had consistently gotten 17 for 2 1/2 years). Another dealership refused to look at it for bad mileage complaint unless dummy light was on and again I was told 14 was normal, and that V6 was actually worse than V8 for mileage.
Everything I've read and heard tells me something is causing rich fuel mixture which is causing the excess fuel to burn in the cat and produce the rotten egg smell. What I'm wondering is if I can solve the rich fuel mixture problem, are my converters already too clogged and need to be replaced. I know the warranty on them is 7 yr or 70k.

Any thoughts?

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97 F150, XLT, V6, 5spd, black

 

Bad EGR? Should code out.

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97 F-150 SC Lariat, Styleside, White over Gold, 4.6L (Windsor), Automatic, 3.55 rear end, electronic 4X4, w/ every option of Lariat and ORP packages except the 17" wheels and the 4X4 decals, MODs so far: K&N air box mod, Gibson Super Truck, clear Bugflector II, Leer TSC 600 hard cover, Bridgestone Dueler OWL ATP 265/75 R-16's, TrailMaster Invader N7 shocks, Smittybilt step bars, Ford moulded mud guards, "White-white" head lamps, Bosch platinum + 4's.

 

Have a "CAT - SCAN"

If they do not purr, or meow - they are dead

Sorry - I could not resist - I had to beat Raoul to the punch.

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98 F150 S/C 4.6 2wd Vermillion/Silver,HD Tow Pkg, Boards, Vents, Bug Chaser, DIY "breezer" Tailgate, 5th whl hitch, Tool box, 16" OEM Mag's,
MARVIN Action Figure in coffee cup holder (2 extra MPG with this mod!!!)

 

The only good cat is a dead one

Sorry, I couldn't resist either!

 

When they stop twitching and meowing when You kick them, They're dead

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98 F150 2WD,Bright Red, Regular Cab, 4.2, 3.55, 5 Speed, Superchip, 2 Superchip Decals (I Think They Add 5 HP Each), 3 Inch Bullseye Lift Spindles, Manik Grill Guard,Nerf Bars, Vent Visors, Fog Lights Mounted In Front Air Dam ,2 Kc DayLighters, Back Up Lights, Alpine CD Player, 2 Kenwood Amps, 10 Inch MTX Blue Thunder SubWoofer, Tinted Windows. And Coming Soon: 3 Inch Body Lift Kit, 16.5 x 9.75 American Racing Baja Wheels Wrapped With 33x12.5x16.5 BFG All Terrains

 

I would hound on the dealerships some more. If your gas mileage dropped 3 mpg that is not normal.

 

Either which one you are talking about, they both will eventually stink.

 

Mean Deane,

There is a product out there for chemically cleaning the deposits out of the cats. It can be found at any auto supply house.

There would also be diagnostic codes popping up all over the place. I think the only way they dont work is if they are plugged with carbon and other deposits.

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1999 F250 SD CC, LWB, 5.4L, Auto, 3.73, 4x4, Power TT mirrors w/ marker lights, White, Full Tint, PendaPro SR, FlowmasterDelta 40 series, K&N filtercharger, Superchip(Airbox removed for a second try, maybe in the winter it will be advantagous?)

www.angelfire.com/pa3/spaceace/index.html

 

Actually, the rotten egg smell is associated with a lean mixture.

If your converters are clogged, the engine will barely run. As a test, you can remove the pre-converter O2's, and the engine will come back to life. Remember, if a cat fails, something killed it (ignition miss).