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Discussion Starter #1
Ok, got new exhaust. New Cats too. And I noticed they sometimes smell. (gets pretty rank in the car, but goes away fairly quick) So I figured I might be dumping too much fuel, and maybe O2 sensors might be to blame. (I've never replaced them, so I figured I might as well) So new O2 sensors, reset the computer and took here for a nice long 1.5 hour drive, keeping as constant pedal and speed as possible. Seems the smell is quite a bit better now, but still noticeable at times.

So with all this information I set my scan gauge to show TPS reading, rpm, and closed/open loop.

Here is what I found,

First of all it shows TPS at 19 at idle... Why? And anything above 32 the computer goes into Open loop! WHY? thats like 1/4 pedal!

And second, I found a correlation between when the computer goes into open loop and the cats smelling. When I take off from a light, if I do anything over the 32 TPS mark (where the computer will then go into open loop for a couple seconds, then closed when I start coming out of the throttle while im coming up to speed) I will smell the cats.

Further more, the cats are starting to turn colors! Their brown now, but I fear if I keep driving it they will soon turn blue indicating WAY too much heat. (also magna wont warranty them if they show these signs of heat)

PLEASE HELP!

~MG~
 

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damn.....if your cats are getting that hot then you are likely running lean for some reason.
 

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Discussion Starter #3
the opposite I would think...
 

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nope, sounds like a lean mixture to me....a rich mixure will actually help cool the engine....at the expense of bad mileage.....you notice any white smoke out of your exhaust...thats a sign of a lean mixture....we all want the perfet air/fuel mixture....but its always better to run rich than lean....your car isnt getting enough air or fuel for the proper mixture in the combustion chamber....hense, improper burn and more heat....one of my focus buddies had a lean condition so bad that his header would almost glow red hot.....you could simple have a vacuume leak.....but yeah, the first thing to go are going to be your cats if you are indeed running lean.
 

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Discussion Starter #5
interesting because my gas mileage BLOWS right now....


I really want to know why the computer goes OPEN loop at 1/4 pedal though... I would think it should go Open at say 85 or so...

Anyone have an Idea?!

~MG~
 

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Discussion Starter #6
Just did some research and found that my thoughts were correct. Rich conditions (over fueling) will overheat a cat, to the point of damage. The excess fuel reaches the cat, and by means of chemical reaction (that the converter is originally designed for) heats up as a byproduct of the reaction.

Although a lean condition will cause high exhaust temp, the cat itself is not to blame. I do believe my situation is a rich condition, also because I have no symptoms of a lean condition. (No pinging etc...)

A thought actually just popped into my head... Think It could be a faulty Fuel pressure regulator?


~MG~
 

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You removed your 3rd cat when you did your exhaust, correct?
Did you do anything with the rear o2 sensors or just unplug them???
 

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huh?....i always knew running rich would eventually kill your cats, but i thought that just congested them...not fried em.....interesting.
 

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Discussion Starter #9
You removed your 3rd cat when you did your exhaust, correct?
Did you do anything with the rear o2 sensors or just unplug them???

Rear O2 sensors are disabled in the tune.

~MG~
 

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Discussion Starter #11
I know the new install will take a little while to burn off, but the cats are showing signs of overheating.The smell is also much more powerful than just a new install smell.
 
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