Vehicle: 2001 XJ 4.0 188K , unregistered farm Jeep that runs for an average of 2 hours a week, max speed less than 15 mph and a lot of idling. occasional full throttle donut. only engine mod is I removed evap system and capped vacuum line on intake. I did this because I rebuilt the frame on the back end and got rid of the canister.

I've read up lately on open loop vs closed loop just because it seems to be the flavor of the month on this forum. I've read about O2 sensors in the sticky and that discussing catalog converter removal sticky is no longer frowned upon.

Things I think I know:

open loop vs closed loop in a odb2

2 up streams O2 sensors in my configuration are need by the computer to adjust air fuel mixture in closed loop only.

2 down stream O2 sensors provided feedback to computer in closed loop only on the effectiveness of the air fuel mixture supplied which is based on the upstream sensors input. checks and balances if you will. it also is used to monitor the precats.

not sure the purpose of the precats in-between the set of sensors

what I'd like to know:

please elaborate on the above. I didn't go into voltage differences and the particulars cause I don't think it applies for my questions.

IAW with the mentioned sticky on O2 sensors the down stream do not effect the air fuel mixture and only are for monitoring effectiveness of the upstream and whether basic mandatory emissions are being met. does this apply to the 2001 O2 system?

what do the pre-cats do?

The million dollar question and the reason for my post...

What are the draw backs based on my application of my XJ with running in permanent open loop and the PCM basing air fuel mixtures and timings on preset values?

my fuel economy is already crap based on my uses and not a concern for me. CEL no issue. not registered, no emissions.

Thank you.

 

None.

 

Thanks

 

ye

 

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The 2 oval " pre-cats " in the exh manifold piping...between the sensors ARE your primary cats. The first sensor before each let the computer know how to adjust the injectors for the best burn, and the ones after let the computer know well the cats are performing. The 3rd cat by the xfer case is just to clean things up for the tailpipe smog check. It is not monitored by computer. If you don't care about codes or emission testing you need none of that but the engine runs better with the feedback from your first set of sensors during normal road/ hwy driving. Problem is if you disconnect the 2 nd set the entire O2 sensor system goes into default mode anyway...which is better than having a bad functioning sensor flooding or leaning out the injectors for your set up....yank them out but you might eventually clog the cats from running rich.