Catless system

[92xjlaredo]

so I have a catless setup on my jeep (96 XJ Classic) im only running my upstream O2 sensor to a flowmaster 40 to a tailpipe...as of right now, anyone know of a cheap/easy way to fool the ECM into thinking that its there? also where the hell is the wiring located for the downstream sensor....i cant find it for the life of me, someone welded in an O2 bung at one point but theres nothing but a broke off O2 sensor in place of where it is, everywhere that ive read tells me to get the "black box" which is like 80 bucks...any input on that one?

[Lycaon]

fix your shit. running catless is stupid especially on OBDii. dont try to trick your ecu, its a stupid game and its not going to gain you much in the way of performance. if anything go buy a highflow cat and fix your system

[92xjlaredo]

well the system never had a cat on it since the day i got it and frankly i could care less. without replacing the ENTIRE exhaust system i cant just throw a cat on there as the muffler sits where the cat once did....the whole thing was changed out and it was run for a LONG time with no cat on it, i just dont want it running as rich as it does...dont have to be super high performance at all really just needs to make the CEL go away and make it run decent.

[clean4drxj]

fix your shit. running catless is stupid especially on OBDii. dont try to trick your ecu, its a stupid game and its not going to gain you much in the way of performance. if anything go buy a highflow cat and fix your system

This.. Put a cat on it and the smells will go away and life will be easier. you can get a cat @ summit racing fairly cheap.

[Ktmracer419]

high flow cats are like 40 bucks. get that, move the muffler back like 10 inches, and you are good to go and won't piss off treehuggers.

[Harry]

Do downstream O2s even affect fuel trim that much? Just fix it.

[ct67_72]

Do downstream O2s even affect fuel trim that much? Just fix it.

No they dont. Only monitor cat efficiency.

[92xjlaredo]

No they dont. Only monitor cat efficiency.

well mines a 96 (OBDII) which means it does actually affect fuel/air mixture...

[Harry]

I really don't think so. OBDI didn't even have a downstream O2 after the cat. Pretty sure Dan is right, just the government's way of making sure people don't cut their cats off.

[Burton58]

My downstream o2 isn't connected on my 99 and air/fuel is fine. Only thing it did was set off the check engine light

[92xjlaredo]

well fuck it then.....just gonna pull the bulb and say to hell with a downstream sensor

[Lycaon]

downstream sensor monitors cat efficiency but it also works in conjunction with the upstream sensor to appropriate the fuel trim to the proper specs. think of it like the front is gross adjustment and the rear is fine adjustment, unless something is wrong in the system, then it goes to a default fuel trim which is where your system is now.

[92xjlaredo]

downstream sensor monitors cat efficiency but it also works in conjunction with the upstream sensor to appropriate the fuel trim to the proper specs. think of it like the front is gross adjustment and the rear is fine adjustment, unless something is wrong in the system, then it goes to a default fuel trim which is where your system is now.

yeah i understand that, it goes into closed (or open) circuit...cant remember which...i did a highway run a little while back and got just about 20mpg the whole time so id say thats not too bad.

[ct67_72]

Here is some good info. Read the OBDII part.
http://www.underhoodservice.com/issu...ontentid=39710
Downstream o2 is to monitor cat efficiency.

[ct67_72]

I will add, that this is only true of early OBDII. Late model vehicles do use the downstream o2 sensor to adjust air fuel but its miniscule adjustments to optimize emissions output based on cat efficiency.