+1 install a high flow cat. Cheap, gets the job done, is emissions legal, and won't stink so bad that everybody stuck behind you in traffic will want to walk up and break your face at a red light. Stock pipe is 2.25" downstream of the cat. Go 2.5" the whole way through.

Regarding the rear O2: it is highly dependent on year. OBD-I XJs only monitor the system and set a code. 1996 probably the same 1997-1999 are vague as many people report mileage differences when measing with the rear O2, however the FSM has conflicting wording. My 1999 does not expose an B1S2 STFT value to my scanner, but that doesn't mean that the PCM doesn't take action if the reading is completely out there. When the weather is nicer I'm going to test this and see what happens. 2000+ systems with 4 O2 sensors absolutey use all four sensors for live fuel trim calculations.

 

......and there's a big difference in the rear O2 location '00+ vs '99 down. A/F ratio accuracy drops very quickly the farther the O2 sensor is from the exhaust port on the head. So, if it's located far away from the head, it's not used to measure A/F ratio.

 

Thanks for the info, this skewed a bit lol. Mine is a 91 so only has the forward o2 sensor.

 

What will I gain by going to 2.5''? I'm not really looking to make it super loud.

 

Hippie alert! That link is real cute. Do you really think the feds are gonna come down on an XJ driver living in the sticks, where it's not required at the state level?

 

Do you think that matters? Read the site rules.

Evet driven behind a car with no cat? You get this sudden urge to leap out an punch the driver in the face because the exhaust stinks so bad.

 

Sounds like **** poor tuning...

I'd rather drive behind someone with no cats than drive against someone with those drop in hid kits.

 

I'd rather be around neither, lol. I like to breathe and see.

 

No cat you get a nice raw fuel smell to the exhaust,But a bad cat will give the exhaust a nice rotten egg stink to it.

 

Bingo. Bad cats make the exhaust smell bad. No cat makes the exhaust smell like... exhaust.

We lived without cats for a loooong time, and nobody ever smelled rotten eggs until the cats arrived.


The kind with 4 legs can sure make a house smell bad, too.

 

Moron!!!
If you knew the forum rules you would know what I was trying to get across! If you can read reread my original post saying that we are not suppose to talk about removing emission components. Try reading before you make a dumb A$$ comment!

 

So I replaced my exhaust and I put in a magnaflow high flow cat and a flowmaster super 40 series sounds nice. I have about 1000 miles on the new exhaust and I noticed there is already some black on the tailpipe like it might be running rich. The old exhaust was a stock cat and a muffler with a hole and a rusted tail pipe lol. I was wondering since everything was new should I reset the ECM so it can record the new data and change the air fuel mixture or would it fix that on its own?