96gtchinook

I recently stumbled upon a o/r x pipe and i want to install cats to keep the car from running in "safe" mode. My question is, will universal 3 step cats work, or will i have to buy obdII compliant c ats to keep the engine from running rich?

Thanks

StriderTacticaL

What do you mean "safe mode"? Do you mean running without the CEL coming on? In that case, can't you buy/make some MIL eliminators?

96gtchinook

there is no MIL on my cluster and i have MIL eliminators installed the car is still running sluggish. "safe mode" is when the car notices no cats so it makes the engine run rich to protect.

WannaBeGearHead

Lol never heard of that

Buy a tuner and turn the rear o2 sensors off. I am a little confused as to why you would buy and/or install an O/R midpipe and then want to install cats. Why not just buy a catted mid pipe?

96gtchinook

i didnt buy the o/r pipe it was given to me. Its sounds to much like a truck right now and im hoping to improve the sluggish engine with the cats.

DreamerGT

I always thought the down stream o2's reported if the cats are working or not. The one's before the cats are the one's that make all the adjustments.

cliffyk

Not having cats will not trigger safe, or "limp", mode, even if it were throwing a DTC for bad cats--and there's no way you're running in limp mode without the MIL on.

There is something else wrong if indeed the engine is sluggish--however it may just be the niose effect. When you installed the o/r pipe I bet it got a lot louder and until you get used to it you mind will be uncomfortable that the noise and performance levels don't seem to match...

cbbass123

Yes, pretty much the rear O2s make sure the catalytic converter functions correctly...If clogged, broken or not present, it will trigger the CEL by reading a different voltage than suppose to. It is also said that the rear O2 can compensate small amounts of fuel (air/fuel ratio) for the degraded catalyst. Ford says that it only has a +/- .5 fuel control authority.

cliffyk

I have never seen this, I am curious as to the source of the information?

The fuel trim and catalyst monitoring decriptions in the shop manuals I have make no mention of the rear sensors having anything to do with closed loop fuel trim control, nor do any of system diagrams, or the Ford OBD System Operation Manuals that I have read.

The PCM can force the mix rich and lean in attempting to jolt the rear sensors back to operation (normally only with a "green", less then 500 miles, cat), however this is just a transient test condition initated by the PCM when the rear sensors are "stuck"...

cbbass123

don't remember where i read that....just remember something like that. But i do agree that their main purpose is to maintain catalytic efficiency. It could be that i read that differ manufacturers use the rear for multi-purposes as in changing air/fuel if catalytic failure or degrading occurs. But i read it was very very minimal change. Or I could have read wrong.