Pre-Cat Removal on 4.0L
 

I am new here and have been driving an xj6 for the past while. On a previous car I had, we removed the pre-cats directly after the manifold/turbo. We just gutted them out and put them back in with a "bung" in the o2 sensor holes as to avoid a check engine light.

Has that been done on a 4.0 with any success?

Pre-cats removal on 4.0
 

I am new here and have been driving an xj6 for the past while. On a previous car I had, we removed the pre-cats directly after the manifold/turbo. We just gutted them out and put them back in with a "bung" in the o2 sensor holes as to avoid a check engine light.

Has that been done on a 4.0 with any success?[/QUOTE]

I wold imagine that the pre/post O2 readings might throw a code.

Yeah I Don't think my car threw Codes after removing The primary Cats Doesn't effect anything But obviously removing the primary's will make more of a noise difference than the Down-pipe ones If you do remove the down pipe cats please weld pipe back on don't clamp them, that's just an exhaust leak waiting to happen. :D

havefuninthesurf,

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Cheers,

Don

I have recently got rid of the cats on my 1995 xj6 x330 4.0 and its running a lot better now fuel economy is up as is the power and it sounds great, I've just got a straight through pipe running to 2 cherry bomb back boxes, it is loud when you put the foot down but quiet enough when sitting at 70/80 on the motor way. Not had any warning lights come on the dash since its been done though I've not seen any sensors on the old cat pipes so I don't know if its a different set up to your car

Well i believe there is a probe after the down pipe cats so maybe there is a flow rating but yeah shouldn't have any codes anyway.

My pre-cats degraded and embolized into one of the the mid-cats which completely plugged it. The eventual solution was to gut the pre-cats, remove the mid-cats entirely, weld on a resonator to make up for the sound deadening of the mid-cats, and re-attach the 4 lambda sensors in my North American spec car. It's a quiet as before, and no codes.

Hi, When you say gut the pre cats, you have to take them off and knock the catalyst out and them put them back on? Why not put new pipes on with a the o2 sensors? I am needing to do this and am wondering why I would put the old pipes back. Also. I will be taking the mid cats off as well and would replace with straight pipes back to the resonator/muffler.

There are no pre cats. Those are your cats and then you have post cats. The front cats are monitored the down stream are not. . And yes you can use a 02 spacer but why not just remove the down stream cats. It improve exhaust note a litlle and the exhaust will get a new smell(not as clean) or build a new exhaust system top to bottom and put a turbo on the manifold why youre at it to make the xj6 more than a slug

Turbo unlikely, how about nitrous oxide
 

yes, the manual clearly states that when driving your slug quickly to never make it appear you are trying to drive quickly lest you be laughed at.

Brutal, none of us are going to find a mechanic willing to "job" us a turbo, but I wonder if perhaps nitrous oxide would be ok....??? I presume I could then keep up with an XJ8 from 1998 and spare myself the ghastly noise of the power-drill sounding Jag supercharger (hey, I owned one so I am qualified). :icon_lurk5:

graemem106, how about some pictures of your setup?

The AJ-16 can probably hold a 75 shot maybe a 100 shot of Nos but ill find that out for myself haha. Id like to build headers maybe even without a collector and just have 3 pipes out of both sides :D
Also I do believe the XJ-6 can already keep up with the 98' N/A XJ-8 and I think the xj-6 has more heritage as that I-6 was like the only engine in the body style that was not built directly by ford :)

So if I am understanding the collection of posts correctly:

1) The X300 has "upper" and "lower"(mid) catalytic converters, is this a pair, or four?
2) Either "gut" or remove but make sure to reinstall the O2 sensors.
2) Both or either sets can be gutted or removed with no adverse engine management or code (CEL/SEL) generation impact.

True?


I may have answered some of my questions: Attached is a photo from the parts catalog for reference with part #1 labeled "exhaust downpipe and catalyst" and part #4 "under floor catalyst"

.

There are 4 catalyst bodies. Gutting the downpipes will most likely throw codes. I'm not sure what correction variables this has so I't may do nothing or it may Adjust fuel mixture but not to extremes so you may see a lose of MPG also gutting everything will remove back pressure increasing HP but also decreasing Torque so find the median of back pressure and you are perfect also If you have very short exhaust with little back pressure you risk burning a valve.

So, the Y pipe with the cats had a non repairable hole. I ordered a new Y pipe with no cats from SNGB, see picture. When it got to me it turns out that the intermediate pipe, #9, was not there and no longer available. I had one made. My car is a California spec car, meaning it had four cats, now it has two under the rear seats. we put all four O2 sensors back in. Although as far as I can tell you only need the upper two. The Y pipe is double walled and leaving the rear two O2 sensors out would have caused a leak or required a lot more fabrication. The CEL is on, but that was expected. I'm in Massachusetts, so I no longer have to pass an emissions test. Obviously the removal of the clogged cats, I had intermittent 0420 and 0430 codes, with an open, non-leaking Y and intermediate pipe have given me an extra 25HP:D. There really is no difference in sound with the windows up and down just a little nicer lower sound.

That's awesome. A down pipe option from the factory. Did it bolt right in or did you have to weld it? How much did you pay for the piping?

? What about torque loss. I am at 5,300 ft elevation and would not want to have less torque.

How how in revs do you have to go to feel the HP difference?

Some more info on parts, performance and codes being set?
 

So to clarify:

1) You replaced your OEM down pipes that include the upper 2 cats, with this "Y" pipe shown above that omits cats. What is the part number for that "Y" pipe?

2) You had to fabricate a length of exhaust to go from the "Y" pipe to mate it to the existing second set of cats under the floor pan?

3) You left all the OEM 02 sensors in place.

4) The car runs fine "seat of the pants" but you are setting some codes as the CEL is being set. Do you know what codes are being set?

5) You mention you have gained 25HP. How did you verify that, and I'll echo weisberg's question about torque gain/loss and at what RPM you are seeing the 25HP gain.


I find this an interesting modification and am very curious about unintended consequences though based on the codes you are seeing, and mine will not pass emissions/inspection if the CEL is lit. So any additional info on what you are experiencing after the change is very helpful.

.

Al,

Here are part #'s:

CBC6373 replacement piping

EBC9388 gasket

JZN100024 nut

Any idea what the original application was for this Y pipe?

I see that is for "various" applications including the X300 according to Jaguar Classic Parts. Was this for markets where cats aren't required?

.