I've seen this part diagram posted a few times in various exhaust threads, and it got me wondering if there were any benefit to using the exhaust components below to delete the catalysts, and if so what issues that might introduce such as how the ECU and 02 sensors would adapt or need to be reprogrammed?

http://www.jaguarclassicparts.com/uk...e-non-catalyst


Seems a curious option that Jaguar apparently supported, and I wonder in what markets this was standard.

 

This is an interesting thread where someone mentions that the XJR was not fitted with the upper catalysts, only the underfloor catalysts. Was this true in some markets for the XJR?

https://www.xj40.com/viewtopic.php?t=5669&start=10

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I think he is referring to the (very rare) XJRs built on the older 'XJ40' body style. I recall that these left Jaguar as XJ6s and were sent, with Jaguar sanctioning, to an upfitter for modifications. Engine mods were mild but a firmer suspension and some appearance goodies were added


Cheers
DD

 

Have a peek

JaguarSport XJR - History


Cheers
DD

 

[QUOTE=al_roethlisberger;1340020]I've seen this part diagram posted a few times in various exhaust threads, and it got me wondering if there were any benefit to using the exhaust components below to delete the catalysts, and if so what issues that might introduce such as how the ECU and 02 sensors would adapt or need to be reprogrammed?

I did it this summer. I live in Massachusetts and after 15 years we are only subject to safety inspection not emissions. Besides the obvious cost difference, it sounds a little better, the check engine light is always on. I did not remove the underfloor cats as the shop said they were still ok, but i will replace those with straight pipes when they do clog. I also left all the O2 sensors in and connected.

 

[QUOTE=dagny747;1340294]Any idea what code(s) is being set with the upper catalysts removed and if it is "significant" from a reliability, economy or performance perspective?

Also, if there is no performance/reliability downside to having the upper catalysts removed can something be done so that it doesn't set a code and ultimate a "check engine light" (CEL)?

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My guess, and that's all it is, is P0420/430--cat convertor efficiency .

The O2 sensors, pre cat versus post cat, are expecting to smell something different, so to speak....but without the cats, they're smelling the same thing....which would be interpreted as lack of convertor efficiency.


Cheers
DD

 

i think that the ECU will switch to open circuit (mode) since there is no signal from the O2 sensors

 

It would be theoretically possible to reprogramme an engine ECU to turn off individual diagnostics, but personally I couldn't justify spending the time to do it. If you are keen to remove the downpipe catalysts and desperate to keep the malfunction Indicator lamp (MIL) off, you could try extending the wiring to all 4 lambda sensors and install them either side of the underfloor catalyst bricks. This might "fool" the catalyst conversion efficiency diagnostic, but I've never tried it so don't know for sure.

 

I don't have a code reader although at this point I should. I believe that it was P0420 and 430. Also, when installed he put all 4 sensors back in because the pipe at the bottom is double walled and it was easier to put the sensors back in than do extra welding. I have had no adverse effects that I know of in terms of performance or reliability, although that is subjective. I've had the car since 2000 and it still feels like it drives the same.

 

Hi dagny,
Since the CEL is on, then the ECU is in open loop.
Theoretically closed loop is when ECU gets all sensors signals inputs and gives the relative output commands to the relative units (fuel injectors, spark plugs, for example), this is a varying process since the input signals are varying (ambient temperature, throttle, cooling medium temperature, O2 situation, etc)
Open loop is a mode when ECU outputs one type, not varying, output commands, of course taking in consideration the throttle for example.
The car may be will behave different somehow, economy, performance, throttle responce, etc.
This is general theory.
But since you don't have emission problems at your area, why don't you try the O2 simulators, they simulate the O2 sensor signal and ECU operates in closed loop.

 

Never heard of them before. I'd be willing to try them, have you used them? I found this? Now that I googled it, I see there is whole new thing to learn about:-)

O2 Simulator Straight Cel Fix stainless steel oxygen sensor simulator.

 

dagny,


there are just metal extensions, some kind of nipples, I'm not sure what the sensors will feed back to the ECU, I don't like them, location of this nipple on the exhaust pipe, length of the nipple...I'm not sure.


the check this one


www.o2sim.com/universal-o2-sim-c-76


I bought them, not installed yet, I'll do it during spring and try to locate them under the cover, close to the ECU

 

If the oxygen sensors are screwed into bosses in the exhaust so that they are in the exhaust gas stream in the correct group of 3 cylinders then the closed loop fuelling control of the engine ECU will work correctly, regardless of whether there is a catalyst present. However, the CEL will still be illuminated because the signals from the sensors which should be mounted either side of the downpipe catalysts will be very similar. The catalyst conversion efficiency diagnostic software will detect that signals from these two sensors are not sufficiently different because there is no longer a catalysts between them, if it removed or the sensors have simply been fitted into a non-catalyst downpipe. The failure of the catalysts conversion efficiency diagnostic will cause the CEL to be illuminated. However, the engine ECU is still operating in closed loop mode.

 

Ahh, so I would interpret that to mean there is no performance issue as the engine sensors will be fully operational cooperatively with the ECU. That's good news as that indicates no disadvantage other than an annoying CEL being illuminated.

Now that being said, I wonder if something as simple as a resistor (for example) could be added to the downstream O2 sensor to fool it into not tripping a code and thinking the catalysts are present?

All very interesting

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I think it is the downstream O2S which are used to control closed-loop fuel/air ratio, so you don't want to fake them unless you don't want closed loop operation. The upper sensors provide pre-cat info to the ECU so cat effectivness can be evaluated.
Re a resistor (for example): I would prefer to leave the O2S disconnected so the ECU used a pre-programmed map (I am guessing) rather than have the engine potentially run lean which could cause damage.
I have an ex-Japan car which has no upper sensors, has only the 2 downstream ones, so I expect I could remove the downpipe cats with no adverse effect (no MIL), but I have not tried this.

 

Sorry, what I meant is that as described by Andy (XJREngineer) the car will run correctly with the upper cats removed and run properly in closed loop mode, but you will get a CEL set as the ECU will detect the pre and post cat O2 sensors not reporting the correct delta since there is no cat.

I was just wondering if you could fake the expected "delta" somehow so that the CEL doesn't get illuminated, but still retain full functionality of the pre and post cat O2 sensors so the open and closed loop modes still functioned correctly. I was just thinking out loud

But that being said, Andy's other suggestion that one could possibly move the post upper cat O2 sensor down past the under-floor catalysts might solve the problem as well by fooling the post upper-cat O2 sensor into thinking it was still detecting the upper catalysts?? One would have to experiment of course.


So, with all that in mind, it appears that there is likely no functional or performance disadvantage to eliminating the upper catalytic converters other than the CEL will illuminate reporting an informational versus functional code.

So that leaves the question of whether eliminating the upper catalysts offers any real benefit? Clearly if your old catalysts are plugged, removing them and repairing the problem will be a benefit. But other than potential cost and future maintenance (cat clogging again one day) savings, would there be a performance or other benefit in completely removing the upper cats and going with the factory "catalyst delete" downpipes versus replacing them with new catalysts?

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So that leaves the question of whether eliminating the upper catalysts offers any real benefit? Clearly if your old catalysts are plugged, removing them and repairing the problem will be a benefit. But other than potential cost and future maintenance (cat clogging again one day) savings, would there be a performance or other benefit in completely removing the upper cats and going with the factory "catalyst delete" downpipes versus replacing them with new catalysts?

.[/QUOTE]

The obvious initial benefit is cost vs new catalyst or refurb. The second would be weight, although I think that would be negligible on cars of our weight. The third would be sound and flow of the exhaust. I see no downside to the cat delete pipes and will remove the back cats when they clog. You still have the under floor resonators and mufflers at the back to provide sufficient back pressure in the exhaust system from what I understand.

 

I removed the catalysts on a V12 and I wouldn't do it again if the cataysts were functional. There was no measurable performance difference between the functional catalysts and the cat delete pipes and the exhaust smells without cats. It was a pain to do as well.

 

Removing the cats, pre csts or all of them, will not hurt anything, car will run as well or better(depending on how bad they are clogged up), and will not affect the ecm at all except the check engine light. The first set of o2 sensors are what controls the engine timing and fuel ratios, as long as everything is as its supposed to be as far as temps of coolant and working control sensors, it will run closed loop as it did with cats thereas stated before, the second set of sensors only check cat efficiency. You can cut the wires and nithing bad will happen. Just the light on.
The mil eliminators are just a resistor, fools tge computer into seeing a different resistance, so keeps light off. Poeple have used those spark plug anti oil fouling inserts that take the sensor out of tge fliw of exhaust, which has seemed to have worked well for most poeple. They are tubes that you screw into the plug holes tgen screw the plugs into them. Cheap and easy. Screw the antifoukers into the secondary o2 sensor holes, the screw the o2 sensors into those. Only problem may be that the Brits may use goofy threads, be sure to compare the threads of the antifoulers to the sensors. There are two sizes used for the antifoulers, older US cars used a different style plug, most likely the Jag would use the smaller newer version. From the o sensrs Ive messed with, US and Asian, they were all the same thread. Bet the x300 is the same sunce Furd owned them then.2