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Discussion Starter · #1 ·
Hi, all.

This might be of use to some of you (doubtful), but will probably be a good laugh to those who can locate their @$$ w/o the use of both hands and a GPS.

What you will need:
-Jack & jack stands + tire iron
-Screwdrivers
-A fairly completely ratchet set, metric
-Several gallons of penetrating oil
-The new header!
-A 2000 Nissan Sentra GXE with a failing three way catalyst/header precat
-Beer (optional)
-Two disinterested dogs (optional)
-An O2 sensor wrench set (NOT OPTIONAL, Autozone will loan you one)
-A loaded gun, to shoot yourself in the face for ever thinking this was a good idea.

The offending car:

She's a real gem.

Procedure:
-Jack up the passenger's side and remove the right front wheel, then remove the wheel lining.


You need to pull the alternator, which requires you remove and set off to the side the AC compressor. Both of these (pita) operations require you remove the drive belts, so do that now. There is a much better guide on this here.


Basically you need to loosen the tensioners (two), which are positioned inconveniently. Once that's done, you can slip off the belts.

This is taken standing in front of the passenger wheel well looking down; it's where one of the tensioner bolts is. Again, see the link above.


With the belts off, you can undo the 4 (14 or 16mm, I think) bolts holding on the AC compressor.

The location of the 4th bolt is at the end of the wrench.

Once you get all 4 bolts off, gently remove the compressor and brace it on a box (or something):


Now, try removing the 3 bolts holding the alternator on. They are not easily accessible if you have hands.

Here's two of them. The third is cake (it's on the bracket screwed into the engine block).

Undo the connection bolt under the red cap, unscrew the ground, and pull that f-er out! And put it somewhere safe, these things are ~$100.

Lots of folks will tell you all this wasn't needed (taking out the alt), but I have to say, I don't have the skill/tools to remove the old header with only the clearance afforded with the alternator still installed. In fact, since I had a bit of a boo-boo (I hit a Pontiac), my radiator support and condenser coil +rad are intruding on any space there used to be as well. So, since I needed to flush the coolant anyway, I drained the radiator and took the whole assembly out.

I didn't take an pictures of pulling the rad because it's really easy. Just follow the FSM to drain, then undo the 2 fan plugs, the 3 hoses (in, out, tank), and a few bolts and pull up. Because of my *ahem* collision, I actually had to take the battery out and move the fuse box. You just can't make this sh1t up.

There, isn't that better?

To take the two heat shields off, undo the ~15 12mm bolts. They're probably rusted as F&^%, so spray 'em down with some good penetrating fluid first.

With the shields off, the real work starts. Unplug all 4 o2 sensors from the harness (this is a 2000 1.8, many of you will have only 2 sensors). Using the o2 wrench you "borrowed" you neighbor's car to go to Autozone to get, try very carefully to unscrew them. Remember a new one is $40.

Spray the ever-loving shoot out of them with penetrating fluid and be careful.
 

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Discussion Starter · #2 · (Edited)
Here's another shot:


Next, to get the manifold off, undo the 8 nuts holding it onto the block and the 6 bolts holding it onto the precat. Yes, there are 6 bolts, not 5, and the middle one in the rear is almost impossible to reach. But you can do it!

Unscrew the EGR nut (which is probably rusted too) and pull forward.

Success!

At this point, your header experience will probably diverge from mine. Because my car is rather rusted, I actually had to take out the whole downpipe (there was no separating the precat from the flex pipe). If you're just taking out the precat and leaving your existing flex pipe, there are some bolts (I've no idea how many) holding the two together, and 2 brackets holding the precat to the car. Undo those and you're good to go.


Me, I undid the brackets and let the entire precat-flexpipe-rest of the exhaust assembly fall to the floor. First undo the rubber mount holding the mid pipe on, obviously. I spent some time catching my hair on fir-I mean grinding the rusted-out bolts holding the rear cat to the resonator, since I couldn't reach the bolts holding the flex pipe to the cat.

Yes, this was a disaster:


After a lot of grinding, profanity, and crow-bar use, though:

Things were looking up.

Gosh, I just don't know why my car wasn't working very well..

Note I still can't get those 2 o2 sensors off. And I put a bag over the cat, since it just can't be good to breathe that stuff.


Now! On to installing the new header!

First clean off any remaining gasket with a razor blade and clean it real good. Put the new gasket on and praying fervently the entire time bend the dipstick tube forward. It'll go, I promise, but I doubt you want to break it, so do is slow. Now is a good time to break the top off the dipstick and replace it with some packing tape. Roll eyes.

You may have to fiddle with the EGR a bit. With the header on, screw in the EGR and then wait a second. To install this aftermarket flex pipe (it's an OBX), you have to screw it to the header before you fully screw the header to the engine. Otherwise there isn't room to get a wrench around the 3rd bolt. So, bolt the flex pipe to the header (with a gasket in the middle), and then bolt up the 8 nuts holding the header to the block. Screw in your 2 o2 sensors (make sure you pick the right ones, or your car won't start. You want the 2 sensors that were originally before the precat. These are Air-fuel mixture sensors, not "cat detectors" which is what the other 2 are. They also have the flat, and not square, plugs attached to them).

From here on out things start to suck. The OBX flex pipe is longer, but a few inches, than the stock one. So the rear cat won't fit back in between the new flex pipe and resonator. My solution was to drive, with a free-flowing exhaust, to the muffler shop and have them weld the old cat in. If you do this be warned that is is loud as &$^#, by which I mean really really really f'in loud. There was a Sheriff parked on my block when I drove by, cat in the trunk, and I thought for sure I was done. It's hard to tell you how loud this is.

Anyway, this is what $70 got me:

Not too great, but the car runs.

With everything back installed (be sure to shear off the bolt holding the coolant tank on, and replace it with some Nissan-approved zip ties):
 

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Discussion Starter · #3 · (Edited)
... And that's all I got :)

Disclaimer: I'm not (AT ALL) an expert, so if you actually know how to do this correctly, please let me know and I'll edit the post.

Sidenotes:
(1) I damaged an o2 sensors trying to get it off the old manifold, so now throw a p0130 code (and the car runs terribly). I've ordered a new one, $40 at amazon.
(2) It is illegal, and not very smart, to drive with no cat, resonator, or muffler. It is also terrifying.
(3) Regarding o2 sensors. The 2000 1.8 will run with no downstream (post-precat) sensors plugged in. You'll get 2 codes, the p0141 and p0161, since they're not plugged in. There are a lot of ways around this. I choose to get a simulator for $40, and I'm going to try to make a "heater box" type thing to fool the ecm into thinking that it's not only getting good signal, but it's getting good heated signal.

(4) My best advice is that before you do anything, look under your car. If bolts look pretty rusty, go pay someone else to do it.
 

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geezinondowntheroad
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Nice writeup. :)

Dude, how in hades did your car get so rusty? Is there that much snow & such in your part of Kali, or do you do weekly cruises on the wet sand at the beach?

You don't have to remove the alternator to install a header.
I think he covered that; he had extenuating circumstances, clearance-wise.
 

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Resident Slowpoke
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I already see 1 thing wrong with this process.

The Beer is not optional! :)
I agree. For this kind of wrenching duties a good case of ice-cold beer is mandatory :D.

Nice writeup. This is a perfect example of what happens when things don't go quite according to planned, but as long as it works....
 

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Discussion Starter · #8 ·
Dude, how in hades did your car get so rusty? Is there that much snow & such in your part of Kali, or do you do weekly cruises on the wet sand at the beach?
Hah, no, it's a Pennsylvania car. I think the previous owner regularly parked it in the river, and I have to say I never garaged it (6+ years now). I'm new to California.
 

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Discussion Starter · #11 ·
that is one dirty engine bay, also did you notice any kind of gain from the header, like power or better MPG or better sound?
Don't know about mpg yet, but it does sound a lot worse. Can of bees syndrome. I'm sure with a high-flow cat and muffler it would sound ok, but it really sounds terrible.

As for power... maybe? I think the throttle is more responsive (making the car easier to shift, actually), but it was KO'd for a while, so I don't remember what it felt like before.

I replaced both upstream o2 sensors, but the car still idles *very* rough (bad vibrations, dancing tach). I don't know if this is just a consequence of installing a header. I cleared the codes, and both codes for the heated downstream o2 cat detectors came back, no surprise there. The car is also incredibly hard to restart once warm. :( :confused:
 

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Don't know about mpg yet, but it does sound a lot worse. Can of bees syndrome. I'm sure with a high-flow cat and muffler it would sound ok, but it really sounds terrible.

As for power... maybe? I think the throttle is more responsive (making the car easier to shift, actually), but it was KO'd for a while, so I don't remember what it felt like before.

I replaced both upstream o2 sensors, but the car still idles very rough (bad vibrations, dancing tach). I don't know if this is just a consequence of installing a header. I cleared the codes, and both codes for the heated downstream o2 cat detectors came back, no surprise there. The car is also incredibly hard to restart once warm. :( :confused:
I kno this is like 11 years to late but try swapping the o2 sensor plug ends that's what I had to do with mine runs just as good as it did before
 
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