'00 xj performance questions...

[Cherroarkee]

ok so i have a 2000 xj with the dual cats design and 4 02 sensors. my plan is to purchase Banks torque tube headers (because they seem to be one of the only companies that will mate up with that design). i also wanted to remove or at least delete the 2 cats by either cutting them out and replacing with reg. pipe or hollowing them out and putting a pipe on the inside so they resemble what theyre supposed to be to pass inspection. my question is since i do have 4 o2 sensors. is there a way to use a wideband 02 setup or something of the sort to fool the stock computer into thinking or even adjusting to the newly acquired setup so i don't throw an engine code? i'm not knowledgeable when it comes to all the computer setups as all the xjs before that i had were renix and eliminating the EGR and cat on them made a big difference in performance and mileage. i'd like to build this motor in the future and the wideband already in place would help that but i just wanted some input from people that have done something slightly similar so i know what i'm thinking of doing is either just plain dumb or will make my setup ready for more in the future. so lets get this going!

also on a side note, has anyone done a port and polish on a newer jeep and saw improvement? at least doing the exhaust side cause there seems to be a bit that can be opened up.

 

[wheeling365]

By doing that your going to run the risk of failing the PA emissions inspection. You can also fail the saftey inspection portion which includes a visual check that all emissions systems are present and working as designed. Not only that but if you read the forum rules it clearly states that there will be no talking about bypassing or disabling emissions devices. The MOD's don't take kindly to it around here.

 

[Yoda]

Yeah big No No. When googled that will pop up and makes Naxja look like the are supporting an illegal vehical mod.

 

[casm]

By doing that your going to run the risk of failing the PA emissions inspection.

Not to mention that it's Federal law that the system must remain intact and functional.

Not only that but if you read the forum rules it clearly states that there will be no talking about bypassing or disabling emissions devices. The MOD's don't take kindly to it around here.

I'm not a mod, and I don't particularly care for it.

Not to mention that removing catalytic converters (pre-cat or cat; doesn't matter) and bypassing oxygen sensors doesn't actually gain you anything performance-wise.

If this was 1977 and emissions systems were still a nightmare composed of vacuum lines, air pumps, and voodoo, then yeah, there would room for improvement. Not in this case.

 

[srmitchell]

Its a 2000. That means they had over 13 years to tune the 4.0 litre to run cleanest, and with as much power as possible. My 2001 hauls ass, passes smog no problems (and that's California smog, mind you) and runs awesome. I really don't see how eliminating the factory pre cats and down stream o2 sensors would yield you much gain.

Not to mention that its against FEDERAL law. And naxja rule...

Dumb idea.

And cats help reduce pollution, which is good.

 

[urban yan]

Yeah, don't ditch your cats.

 

[88JeepXJ]

I don't suggest ditching the cats. It will free up a few horses but not worth the pollution. You can get some highflow cats but I'm not sure how much OBDII will like those.

 

[Talyn]

Its a 2000. That means they had over 13 years to tune the 4.0 litre to run cleanest, and with as much power as possible.

They had 13 years to choke it down. Compared to my 91 my stock 2000 was a dog. Same trim, same everything. Most of the problem lies in the PCM and its closed loop operation. They might have made it run cleaner but at the cost of performance.

It will free up a few horses

Proof of this?

has anyone done a port and polish on a newer jeep and saw improvement? at least doing the exhaust side cause there seems to be a bit that can be opened up.

If you still have the stock head putting any effort into it is a waste. They are known to crack.

Get a rugged ridge or any other header that is meant for a 00-01 XJ.

 

[Cherroarkee]

thanks for the input guys and yeah i guess i'll leave it alone. it is running great i just got it all apart now replacing the rear main, a leaky manifold gasket and valve cover. i'm just gonna get bank's header and get a cherry bomb after the cat. it'll sound great and freer flowing. im sorry if the whole removing cats was a no no on here. i wasn't worried for the fact in the poconos they dont do a emission check and i had an 91 240sx with a SR20det in it and the guy didn't even think twice (he said it was the cleanest engine bay he looked at, hehe).
i'm just not used to just letting most things just be in a car. even if theres been over 13 years of engineering into the 4.0. i mean chevy has been around forever and my moms '10 malibu and its been in the shop over 20 times for things they can't seem to get right, idk.

on the plus side thank you Talyn for the info about the rugged ridge headers. everything else is practically double what the black coated steel ones are going for! i'm going to be gettin a pair of them instead of the banks just because they're just a wee bit more in my price range.

i'll be doing a write up in the future when i put my iPad in the dash!! pretty excited and i think i got everything to start the project. :: RULES!!!

 

[casm]

thanks for the input guys and yeah i guess i'll leave it alone.

Good call. More:

im sorry if the whole removing cats was a no no on here. i wasn't worried for the fact in the poconos they dont do a emission check and i had an 91 240sx with a SR20det in it and the guy didn't even think twice (he said it was the cleanest engine bay he looked at, hehe).

Just to add some perspective on this that's completely outside of the legal reasons: I'm in a no-test area for emissions as well, but spent 10 years prior to that dealing with CA smog requirements so have a pretty good handle on how bad they can be. While I was there, I owned a number of vehicles with and without emissions control equipment depending on year of manufacture.

What I found was that you probably don't want to own a vehicle made between about 1975 and 1985 if it has emissions equipment because it'll be a nightmare to deal with, both from a maintenance and a passing-inspection standpoint. The engine, electronic, and emissions technology of that time just wasn't developed enough yet to not adversely affect performance - and while there are definitely some exceptions to that, there aren't many that were in mainstream manufacture at the time.

Fast forward to when your XJ was manufactured. Technology had improved to the point where not only was the emissions equipment no longer a stumbling block to performance, but was required to be functional in order to make full use of that performance.

Using the oxygen sensor bypass idea floated earlier as an example of this: yes, they can be bypassed and the PCM effectively fooled into believing that they're in a legitimate state. Now consider that readings from the oxygen sensors contribute to controlling fuel/air mixture and timing across a range of engine speeds, loads, temperatures, and other criteria. If your bypass items are giving the PCM a constant reading, those values that they're sending to the PCM are going to be invalid across a huge range of conditions. Kiss goodbye to linear performance, fuel economy, and longevity of a number of service items.

i mean chevy has been around forever and my moms '10 malibu and its been in the shop over 20 times for things they can't seem to get right, idk.

If it's been back that many times and is that new, it sounds like she got a lemon. If I were in her shoes I'd probably be looking into having GM take it back - but you can't necessarily use her one vehicle's issues as being representative of across-the-board problems or drawbacks with a specific type of system, particularly when relating those experiences to other makes and models. At that point, you're effectively comparing apples and oranges.

Good luck on the Banks headers; I've been playing with the idea of a set on my 2000. Let us know how it goes once you've got them in.

 

[Talyn]

Using the oxygen sensor bypass idea floated earlier as an example of this: yes, they can be bypassed and the PCM effectively fooled into believing that they're in a legitimate state. Now consider that readings from the oxygen sensors contribute to controlling fuel/air mixture and timing across a range of engine speeds, loads, temperatures, and other criteria. If your bypass items are giving the PCM a constant reading, those values that they're sending to the PCM are going to be invalid across a huge range of conditions. Kiss goodbye to linear performance, fuel economy, and longevity of a number of service items.

The down stream O2 sensors contribute no information to performance or the air-fuel ratio. The PCM gets data from them just to verify that the two precats are working. Siming them out will not do as you described.

 

[casm]

The down stream O2 sensors contribute no information to performance or the air-fuel ratio. The PCM gets data from them just to verify that the two precats are working. Siming them out will not do as you described.

Interesting, and understood re: checking the cat/pre-cat functionality. Any recommendations on a good overview for this? I'd like to do some re-reading on it; it's been a while and it wouldn't be the first time my memory went. Could have sworn it was used to alter fuel introduction to lean out or richen the mixture as well as advancing or retarding timing.

 

[Talyn]

I think the FSM has a small blurb about it. I really don't have anywhere to point you. However, I have read other manufactures (if not all lately) do use the rear O2 sensors to some degree to control AFR. The amount that the rear sensors can contribute is limited and usually only under fault conditions such as a bad cat. However, the 4.0L PCM just looks at them to see if the cat is working or not.

I wonder if AERA has an article about this.

 

[casm]

I think the FSM has a small blurb about it. I really don't have anywhere to point you.

Cool, I'll dig through it again. FWIW, that's now ringing some bells from when I went through oxygen sensor hell a few years back.

However, I have read other manufactures (if not all lately) do use the rear O2 sensors to some degree to control AFR. The amount that the rear sensors can contribute is limited and usually only under fault conditions such as a bad cat.

This may have been getting mixed in with what I was thinking of in terms of the XJ's operation.

I wonder if AERA has an article about this.

Good question... I've never had a compelling reason to join them, but this is a case where I'd definitely like a peek at their archives.

 

[gradon]

If I had a 2000-01 w/ the cali package, I'd do exactly what you planned to do and ditch them underhood bakers and sim out the precat sensors(you can y the output of one), but leave the main upstream and downstream sensors.

 

[casm]

If I had a 2000-01 w/ the cali package, I'd do exactly what you planned to do and ditch them underhood bakers and sim out the precat sensors(you can y the output of one), but leave the main upstream and downstream sensors.

What performance gain would you anticipate from doing this?

 

[gradon]

I know the long-tube Borla w/ downpipe flows better than those cast manifolds and pres do(and weigh less, and less heat).

 

[casm]

I know the long-tube Borla w/ downpipe flows better than those cast manifolds and pres do(and weigh less, and less heat).

Sure, with you on that. I should've phrased my question more accurately, though: what gains would you anticipate from bypassing the oxygen sensors and removing the pre-cats?

 

[srmitchell]

Do those RR headers fit well? Not much info is available.

 

[Talyn]

Ive heard a few people use them. None reported any issues