Desert Pearl

I am currently in the market for a y-pipe. Well to make a long story slightly less long, I haven't found one that replaces my front-side precat. I took a trip to my local Nissan parts dept and found something very interesting.

The 2000 Maxima had two different exhaust manifolds for the front-side of the car... one for CA emissions and one for federal. The 2001 Maxima has only one exhaust manifold... the same as the 2000 CA emissions Maxima. This means that all 2000 CA emissions Maximas and ALL 2001 Maximas (regardless of your emissions setup) have a precat on both sides of the motor. BUT this also means that someone with this setup can work around it by buying a 2000 non-CA exhaust manifold (P/N = 14006-31U00) and get rid of that stupid precat.

I believe that SEVERAL people on this board will be glad to hear this, because it seems that many have complained about only being able to get rid of one of their precats when they put on their aftermarket y-pipe.

The price for this part at my local store (no discount) is $144.77. It could probably be found for well under $100 with a good discount or even used. Sounds like money well spent.

maxman2k

a couple questions....first, if you want to do this, wouldnt you have to buy 2 of these? and also i think that the CA emissions involves more than the pre-cat, right? and if so, wouldnt that trip some kind of sensor if the pre-cats are removed?

y2kse

iTrader: (1)

No doubt about it. The ECU would <b>FREAK OUT</b> if you put a Fed-spec front exhaust manifold on a CA/NLEV-spec Maxima. To make it work, you'd not only have to replace the CA/NLEV-spec front manifold with a Fed-spec manifold, you'd probably have to replace the CA/NLEV-spec ECU with a Fed-spec ECU as well. And last time I looked, ECUs were running just a wee bit more than $144.00.

But hey, it's a nice thought.

Desert Pearl

Just a few comments here.

1) There is more to the CA emissions that the precats. There are two extra O2 sensors that would have to have extra bungs welded onto the new y-pipe, if you got one that didn't have these already.

2) The rear exhaust manifold doesn't have the precat built into it like the front one does. Actually, this was my first idea... to buy a "rear" exhaust manifold and replace the one on the front of the car with it. Sounds like a good idea and upon my initial inspection, it seemed like it would work, however the bolt pattern around the center exhaust port is reversed on the front side manifold.

3) I'm not so sure that the current ecu would object to this. I don't recall hearing anyone with an aftermarket y-pipe having issues. Why would the ecu allow you to remove the rear precat, but then object when you removed the front precat? They are both done the same with one O2 sensor just prior to the precat and another just after.

Keep in mind that I don't have a y-pipe yet, so there may be more that I don't know. If you have more info, please feel free to enlighten me.

2k1spdfrk

Very observant, I have only had my 2k1 for about month now and it has been to damn cold and snowy here in NH to look around. I do like your idea and you theory on the ecu and sensors make sense, at least to me. Keep me informed as to any info u come across. I will also be checking in here as well.

psing23

ye i hope some more "experienced" people come and see this and post something about it cause im gonna keep track... seems like a great idea... i wish there was a list or something that showed the differences bet a fed car and a ca car... does anyone know of such a list? that would be great to have

y2kse

iTrader: (1)

Fair enough.

1) Correct. And the function of the O2 sensors mounted in the new Y-pipe would be . . . you guessed it . . . to measure the reduction in emissions between them. But with the front pre-cat removed, there won't be any reduction in emissions between them. As a result, you WILL get a check engine light.

2) Correct. The rear O2 sensor is mounted in the rear pre-cat housing. Frankly, I'm not sure why removing the rear pre-cat doesn't generate a check engine light. I just know that it doesn't. Obviously the critical measurement of emissions reduction occurs across the front pre-cat rather than the rear pre-cat.

3) Actually there are THREE O2 sensors in the exhaust system, two in the front pre-cat section and one in the rear pre-cat section.

Now here's a little experiment you could try. See if you can find a used CA/NLEV-spec front exhaust manifold and gut the pre-cat. Then replace your stock manifold with the modified manifold and report your results here. I think you'll thank me for not recommending that you start by gutting your stock manifold.


[Edited by y2kse on 03-10-2001 at 09:15 AM]

y2kse

iTrader: (1)

Me too, psing23.

Nissan has a list. And I suspect it's probably buried somewhere in the service manuals.

The real key would be to find out if there's a difference between a CA/NLEV-spec ECU and a Fed-spec ECU. If there isn't any difference, then the question becomes how to get the CA/NLEV-spec ECU to behave like the Fed-spec ECU when it comes to measuring the emissions reduction ACROSS the front pre-cat. Obviously, the CA/NLEV-spec ECU takes this measurement into account and the Fed-spec ECU doesn't. Once that piece of information is known and the CA/NLEV-spec ECU can be modified to emulate the functioning of the Fed-spec ECU, the games can begin.

[Edited by y2kse on 03-10-2001 at 09:32 AM]

y2kse

iTrader: (1)

OK. You guys got me thinking.

I called Dave Barron at Southpoint Nissan and asked him if there was a difference in ECU part numbers between a Fed-spec Max and a CA/NLEV-spec Max. He told me that different models (GXE/GLE, SE) have different ECU designations, but they all share one thing in common.

The 2K Maximas have DIFFERENT ECU part numbers depending upon whether they're Fed-spec or CA/NLEV-spec and the 2K+1 have the same part numbers. That means, of course, that ALL 2K+1 Maximas conform to CA/NLEV emissions specifications.

To modify a CA/NLEV-spec Max to conform to Fed-spec standards would cost AT LEAST $900.00. This includes the cost of a new Fed-spec ECU ($755.00) and a new exhaust manifold ($144.00). This also assumes that there are no other modifications required to change emissions specifications from CA/NLEV-spec to Fed-spec.

I don't know about you guys, but paying $900.00+ to gain 5 hp is a little rich for my blood. And you obviously won't be able to pass CA/NLEV emissions testing with a Fed-spec vehicle.

Any other questions?

Desert Pearl

You have some good advice here with your experiment. I don't think I'll try it because I could pick up a used exhaust manifold for the same price as a front precat. The gutted cat probably wouldn't help performance at all (too big = lower velocity = less evacuation), so it would be used for this experiment only, even if the check engine light didn't come on.

My car has FOUR O2 sensors in the exhaust. They are color coded red, blue, white and black. There is one before and after each precat on both sides of the motor. This is why I don't feel that the ecu would treat the front precat any different that the rear one. I doubt that they would put encode the CA emissions with a requirement for a front-side precat but not a rear one. Think about that for a second. I can't picture an engineer saying "Well, we'll monitor half of the motor and make sure it's running clean. The other half, who cares what it does; we still have the main cat back there." I've seen stupider things, but I don't think this is the case.

One more comment. I've heard that if you get a check engine light, that they will eventually clear themselves (I recall hearing someone say "about 40 cycles"). If that's the case, the annoying light on your dash is only a temporary problem and will go away in a few weeks. You could also put a switch inline with your light so you could disable it whenever you want (or you could just cut the wire!). My only problem is what if the ecu sees something and tries to correct for it by retarding my timing or leaning out the car. I hope it won't do something like this, but I'm not 100% certain.

Also, this annoying check engine light seems to be inconsistant on our cars. I have read some posts with people claiming that the JWT POP Intake set off their light. This was not the case for me. Wonder why???

Desert Pearl

This was definitely not my intention going into this. I do feel that the front precat is no different than the rear one. So, I'm basically just extending the y-pipe idea to incompass the restriction in the front exhaust path (front precat). I still feel that the car would respond no differently than if you simply installed an aftermarket y-pipe, but you are almost doubling the HP gain by also doing the manifold/front precat. That seems well worth $144 to me!

y2kse

iTrader: (1)

Right you are. I'm looking at a diagram of the CA/NLEV-spec intake system as we speak. There are, in fact, FOUR O2 sensors all of which are housed forward of the main catalytic convertor. Two O2 sensors surround the front pre-cat and two surround the rear pre-cat. I'm also looking at a diagram of the Fed-spec intake system. The Fed-spec vehicle has THREE O2 sensors. One is housed in the front down-pipe, the second is housed in the rear downpipe, and the third is housed aft of the main catalytic converter.

y2kse

iTrader: (1)

Are you prepared to test your theory, Desert Pearl? Or should we simply assume that you know more than the engineers at Nissan who designed the differences between the Fed-spec and CA/NLEV-spec vehicles?

Desert Pearl

Sounds like a challenge to me. Regretfully, with my underdrive pulley already on order, I'm a little low on car funds right now. I will probably go ahead and buy the exhaust manifold, but the y-pipe will have to wait until early May, I think.

Desert Pearl

Hey Y2kSE, what do you think about this. Suppose I buy the exhaust manifold from a 2000 Federal Max and a 2000 Federal aftermarket y-pipe. That leaves me with two O2 sensors with no place to go. What would happen if I spliced their leads together, lengthened the wiring to reach the main cat, added a bung and plugged it in just after the main cat??? That way, the 2nd O2 sensors would still be "seeing" a catalytic converter.

What do you think???

psing23

ye thats what i was thinking about too... just to relocate the o2 sensor after the main cat... cause then it will find a change and not cause a check engine light... im sure something could be done... if lets say i change the car from a CA to Fed emisions would i not pass emisions? how does a Fed car pass emissions then? is there a different program that they go into? cant i just change the sticker under the hood to say Fed emissions? lemme kno

y2kse

iTrader: (1)

There's much more here than meets the eye, Desert Pearl. According to the exhaust manifold diagrams, a Fed-spec front exhaust manifold won't even bolt up to the stock CA/NLEV-spec Y-pipe. The front pre-cat gets in the way. On the other hand, if you replace the exhaust manifold and the Y-pipe simultaneously, you might be able to achieve a proper fitment. But that still leaves the problem of acquiring or fabricating the piece between the main cat and the resonator on Fed-spec vehicles that houses the rear O2-sensor. And whether the ECU would respond properly if the positions of the O2 sensors were changed is problematic.

Frankly, I think it's more trouble than it's worth. If it works, you probably won't gain more than about 5 additional hp. But I'd encourage you to try it. Why, you ask? Because I have nothing to lose.

[Edited by y2kse on 03-10-2001 at 01:36 PM]

PKO

I was thinking of doing the same thing except I already have a CA Cattman y-pipe and would probably need a custom made pipe to replace my front pre-cat. I got an e-mail from Brian Catts who said he was working on a solution to this pre-cat, O2 sensor problem. He didn't say when his solution will come. Desert Pearl, there's probably quite a few people interested in your experiment. Give it a try and let everyone know what happens!

y2kse

iTrader: (1)

I'd be interesting to know what Brian is up to. Obviously, removing the front pre-cat and "fooling" the O2 sensors into thinking it's there would be very cool indeed. I might even think about buying a Y-pipe if Brian could pull that off. Of course, I won't consider buying one before that. Engine longevity is at least as important to me as performance, and I don't like the idea of unbalancing the exhaust flow between cylinder banks by removing only one of the pre-cats. It would be like installing a NOS setup and putting larger injectors into only one bank of cylinders. You'd still get a performance increase, but it probably wouldn't be very good for the engine. Know what I mean?


[Edited by y2kse on 03-10-2001 at 05:46 PM]

Desert Pearl

I too would like to see what Cattman is working on. If I do try this manifold swap, I would definitely be installing it simultaneously with a Federal emissions 2K y-pipe, so I didn't have to make something to replace the front precat. As far as making something to plug the downstream O2 sensor into, that's cake. Belanger's Custom Exhaust, the place that did my cat-back can do it in a couple of minutes.

Thanks for all of the input guys. If Cattman doesn't offer something by early May, I think I'll proceed with my original plan.

Has anyone here removed the O2 sensors after the cats to see if they'll get a check engine light? How about if you leave them connected but just tie wrap them outside of the exhaust and plug the hole in your pipe? Does anyone have any experience with either of these situations to say for certain if they'll generate a check engine light? I may test these out tonight.

PKO

Engine longevity is at least as important to me as performance, and I don't like the idea of unbalancing the exhaust flow between cylinder banks by removing only one of the pre-cats. It would be like installing a NOS setup and putting larger injectors into only one bank of cylinders. You'd still get a performance increase, but it probably wouldn't be very good for the engine. Know what I mean?


[Edited by y2kse on 03-10-2001 at 05:46 PM] [/I][/QUOTE]I'm concerned with this unbalance as well with my y-pipe. I don't like possibility of my engine slowly self destructing. Hopefully, someone will come up with something soon!

PKO

2) Correct. The rear O2 sensor is mounted in the rear pre-cat housing. Frankly, I'm not sure why removing the rear pre-cat doesn't generate a check engine light. I just know that it doesn't. Obviously the critical measurement of emissions reduction occurs across the front pre-cat rather than the rear pre-cat.

[Edited by y2kse on 03-10-2001 at 09:15 AM] [/I][/QUOTE]Brian Catts solved the problem on his y-pipe by doing the following. Instead of placing the rear O2 sensor on the pipe after the non-existant rear pre-cat, he mounted it on the pipe connecting to the front pre-cat. So basically, there are two O2 sensors downstream of the front pre-cat. The ECM thinks everything is fine. It just doesn't know it's monitoring the front pre-cat instead of the rear one. The ECM can be fooled!!

psing23

so can all the sensors be placed after the main cat? this would fool it too right?

y2kse

iTrader: (1)

Sort of. It appears the idea would be to install a Fed-spec front exhaust manifold, a Fed-spec Y-pipe, an O2 housing in each of the downpipes, and two O2 housings aft of the main cat. The blue O2 sensor would go in the front downpipe. The white O2 sensor would go in the rear downpipe, and the red and black O2 sensors would go in the housings aft of the main cat. That way, O2 readings would be taken on both cylinder banks across the main cat instead of the pre-cats. And both pre-cats could be eliminated without damaging the engine or setting off a check engine light.

In theory, that should work. If anything, the drop in emissions across the main cat should be GREATER than across the pre-cats.

So who's going to be the first to try this out?