2003 s type r cat delete
 

I just picked up a 2nd s type r from a salvage dealer. Its a pretty clapped out 2003. I'm planning on using it for track days and autocross. Along with other issues I"m dealing with, the exhaust is already gone from the car. The Stock cats are still on and all 4 O2 sensors are there. the cats look pretty nasty and slightly choked up from the one side I pulled off. Does anyone have some useful advise on how I can remove them and not set off a limp code or DTC code? I'm planning on running just a x pipe resonator. Once again this will be a track day only car so no need to keep them.

I know someone or a few have already done this and are running around like this as a daily driver. How did you cheat the 02 sensors and keep the fuel trims accurate?

In my quest to do this cheaply and effectively, If I just gutted the cats, and then replaced them, How effective are this O2 sensor cheaters that go into the downstream port?

anyone

Cheap & effective are mutually exclusive in this case...

Have a read of this thread https://www.jaguarforums.com/forum/x...-remap-140980/

The minicats will work in keeping the Check Engine Light off and codes being set.

However your fuelling will be a bit screwed up because the downstream sensors are also used to manage the closed-loop fuel trims.

The only way to do it "properly" is within the ECU, either with the IDS/SDD diagnostic system, or an aftermarket tune (but i'm not aware of any aftermarket tunes that have acheived this yet on the early pre-2006 ECU's).

thanks for the link. If the Mini cats are used, how bad did your experience show with fuel consumption? I will be running a small fuel cell.

Well Sid's N/A 4.2 went from averaging 9.8L/100km on the highway down to 9.2L/100km after ditching the minicats.

But the bigger thing in my eyes is the transition from closed-loop to open-loop. You see the dyno graph in that thread with the Air-Fuel-Ratio, there is a big lean patch with the minicats fitted.

I suspect it's because the minicats slow the response of the downstream cats, so going WOT there is a second or so where the measurements are a mile off, and that's where the lean spot is.

I personally would never use minicats on one of these engines, not after what we've learnt from this testing.

I noticed that lean section on the graph. You are positive it is related to the mini cats? If that is the case I might just have to bite the bullet and buy a set of 200cell cats and put on here unless you have a better cost effective solution?

Can't be 100% sure without more testing (and for the time being that's not going to happen) but it certainly looks that minicats were the reason for that strange AFR curve.

Guys, just for my info...

I know what an OEM cat is.
I know what a 200-cell cat is.
I know what no cat whatsoever is.
What the hell is a Minicat?

https://www.jaguarforums.com/forum/a...p-img_0810.jpg

https://www.jaguarforums.com/forum/a...p-img_0811.jpg

https://www.jaguarforums.com/forum/a...p-img_0812.jpg

https://www.jaguarforums.com/forum/a...p-img_0815.jpg

It's a small extension to the O2 sensor which has a miniature catalyst honeycomb in it, to trick the sensor into reading "clean" exhaust gas.

Thanks, Cambo.

My '05 STR has 78k miles on the clock. I have 4 new Denso sensors, 2 new 200-cell cats and 2 plain extenders (see pic) standing by, just waiting for the MIL.

My question - how much change to normal fuelling can I expect to see once I have fitted all the above?

Well you saw the difference to the highway fuel consumption on the XJ.

I can't tell you exactly how much difference.

But for sure it's not going to be "right" with the downstream sensors being fooled by extenders or minicats.

Wow, that difference is about 2 mpg UK!

So the erroneous low-oxygen signal from the sensors by the the minicats causes the ECU to unnecessarily increase the richness of the fuel mixture, reduce the mileage and mess up the fuel trims. I get that.

What puzzles me is why you would use a minicat in the first place. A sensor in the downstream airflow from a 200-cell cat would signal too much oxygen. As it is removed further away from the main airstream (with an extender) there will be less airflow across the sensor, and it would eventually signal too little oxygen. Somewhere in between is a position where the sensor signal would be the voltage expected by the ECU if OEM cats were in use. Any way this position could be determined, maybe to the nearest 1/4"?

Maybe it's not possible. Maybe I have got the theory wrong. Can you put me straight, Cambo?

All of the extenders will cause a slow reaction of the O2S to the mixture change. It will hurt all of the transient conditions and it may lean a mixture in a cruising conditions (this will affect a milage, increasing a fuel consumption). Transition from a cruising to a power enrichmet will be affected too, it may cause a detonation (in a hot weather). Also, in some situations a EGT may rise too high, causing a damage to a cat converters and/or exhaust valves/seats.
The best way to fit a custom cats or to remove a cats is to flash a proper tune and leave secondary O2S in place.