PASSENGER SIDE
Remove the 3 nuts connecting the cat to the manifold flange using a deep 14mm socket. Once free move it towards the rear of the vehicle taking care not to damage the O2 sensor. Take the cat to your work bench and using a 22mm wrench remove the O2 sensor. Unlike the down tubes you will notice that the sensor is not threaded directly into the cat bung but is instead threaded into an adapter. On mine the sensor was frozen in the adapter and both came out together. Simply place the O2 sensor adapter in a vice, tighten the jaws on two flats, and remove the O2 sensor from adapter.

Take the O2 sensor that was removed from the cat and remove the old crush washer and install a new one and then install the sensor into the header.

Next using a 12mm standard socket remove the clamp for the power steering line stay and move the lines up and towards the front of the vehicle. You will need to do this to access the front most manifold nut.

With the lines out of the bracket begin loosening the EX manifold nuts using a 14mm deep socket. Some of the studs may back out with any luck they will be the three studs you will need to replace. Once you have removed all 6 nuts remove the manifold it should come out right over the frame rail.

3 of the OEM studs are too long for the AC header flanges. To fix this you will have to remove the 3 studs indicated in the pictures below and replace them with the shorter studs. Also inspect the 3 OEM short studs for damage and excess corrosion, if damaged replace as needed.

Long OEM stud on the left and the short stud you will need to install on the right.

Long stud locations

If the studs are not too stubborn they can be removed using an 8mm socket. Once you have removed the 3 long studs, and any damaged studs, you can now install the new studs. Place a bit of high temp Loctite on the studs and install them to between 9.4 to 12.3 ft lbs. Once installed clean the EX manifold gasket surface using the scotch brite pad and finally wiping it down using a little bit of brake cleaner.

Time to install the header. The EX studs I purchased came with new nuts but after looking at the diameter of the nut flange vs the size of the holes in the header flange I decided to re-use the OEM nuts. The OEM nut has a much wider flange and should do a better job of applying even pressure to the flange.

New aftermarket nut on the left and OEM on the right.

Take your new exhaust gasket and set it in place on the cylinder head. Next put a bit of the anti-seize on all 6 ex studs. Carefully work the header into position taking care not damage the O2 sensor and slide it onto the studs. Temporarily secure it in place using two nuts near the center. You will notice that the holes in the flanges are much larger then the studs they sit on. This can cause misalignment of the header to the gasket surface, possibly resulting in an ex leak, or misalignment of the header with the ex port possibly negating the potential performance gains from installing headers.

To combat this I made 2 installation dowels at work to ensure that everything would be aligned properly. You can see in the pictures below that the dowels center the stud in the flange holes. The nuts for the flange must be torqued in a specific sequence to ensure that the flange stays flat and true.

Centering dowel

Centering dowels installed in positions 5…

and position 3

Following the guide below, taken from the FSM, apply between 21.0 and 24.6 ft lbs of torque to each nut in the order shown. Also shown below you will see two nuts indicated by red arrows for each side. These are nuts that you will not be able to put a socket on because thay are obscured by the header tubes. What you must do is use a wrench and approximate the torque applied to the first nut. Once the first two nuts are torqued remove the alignment dowels and install the nuts. Torque 3 through 6 and your first header is installed.

Tightening pattern

Obscured nut locations

Removing the centering dowels

Resulting in a nicely centered header.

Re-install the power steering line clamp and then back to the bench to install the CEL and the rear O2 sensor in the passenger side down tube. Place a small amount of anti-seize on the O2 sensor and the threaded end of the CEL and thread the CEL in as far as it will go and tighten the locking nut. Install the O2 sensor into the CEL and then loosen the CEL lock nut so the CEL can move freely this will allow you to clock the CEL to the correct position once the down tube is installed.

With the CEL and O2 sensor now installed you will need to install a new crush washer on the 3 bolt flange end of the down tube. Using a pick or flat blade screwdriver pry up an edge of the old gasket and work it off of the tube, once off slide on the new washer.

Pic showing how the crush washer interacts with the bevel cut into the header.

New crush washer compared to the old one on the right. You can see how the washer crushes to conform to the shape of the bevel in the cat or header.

Now take the down tube and work it into position under the vehicle. It takes some doing but take your time and take care not to damage the O2 sensor. You also need to make sure that the CEL stays pointed towards the front of the vehicle, if it ends up pointed towards the rear there is not enough clearance to spin it around once the tube is in place.

Once the tube is in place thread in the 3 bolts that attach the down tube to the header, verify that the crush gasket is still in place as they can fall off while the tube is being positioned. Using a 17mm standard socket start the bottom 2 flange bolts by hand. Once the bottom 2 bolts are installed thread in the top bolt using a 17mm standard socket and the 3/8 swivel drive. The swivel drive will allow you to get around the CEL which is blocking access to the 3rd bolt. With all 3 bolts started evenly tighten them down to 21.0 to 24.6 ft lbs. When finished you should have an even gap, all the way around, between the flanges of the down tube and header. Next clock the CEL to a position with clearance on all sides and snug down the locking nut.

Pic showing the CEL orientation and the down tube installed.

 

DRIVER SIDE
Simply follow the directions above (driver side same as the passenger side) with the following exceptions.

2 of the OEM studs are too long for the AC header flanges. To fix this you will have to remove the 2 studs indicated in the pictures below and replace them with the shorter studs. Also inspect the 4 OEM short studs for damage and excess corrosion, if damaged replace as needed.

Long OEM stud on the left and the short stud you will need to install on the right.

Long stud location

On the top of the old manifold is a plug that you will need to transfer over to the header. Simply remove the plug, clean the threads, apply anti-seize, and install it in the header. If you can not get the plug loose a replacement is available from Nissan by ordering 14052-21R00. Thanks to Mirage for coming up with the number.

Centering dowel should be installed in locations 5 and 6 of the FSM tightening order guide.
Following the guide below, taken from the FSM, apply between 21.0 and 24.6 ft lbs of torque to each nut in the order shown. Also shown below you will see two nuts indicated by red arrows for each side. These are nuts that you will not be able to put a socket on because thay are obscured by the header tubes. What you must do is use a wrench and approximate the torque applied to the first nut. Once the first two nuts are torqued remove the alignment dowels and install the nuts. Torque 3 through 6 and your second header is installed.

Tightening pattern

Obscured nut locations

Now take the down tube and work it into position under the vehicle. It takes some doing but take your time and take care not to damage the O2 sensor. You also need to make sure that the CEL stays pointed towards the front of the vehicle, if it ends up pointed towards the rear there is not enough clearance to spin it around once the tube is in place.

Once the tube is in place thread in the 3 bolts that attach the down tube to the header, verify that the crush gasket is still in place as they can fall off while the tube is being positioned. If you look at the flange you will see that the CEL is blocking access to installing the top bolt. You will need to cut down this bolt, shorten it, in order to thread it in. The bolts that AC supplies with the headers are absurdly long so cutting it down should not cause an issue just don't go to short. Using a 17mm standard socket start the bottom 2 flange bolts by hand. With all 3 bolts started evenly tighten them down to 21.0 to 24.6 ft lbs. When finished you should have an even gap, all the way around, between the flanges of the down tube and header. Next clock the CEL to a position with clearance on all sides and snug down the locking nut.

Pic showing the CEL orientation and the down tube installed.

Once you have both headers and the both down tubes installed simply re-install the Y pipe , don’t forget the single mounting bolt next to the flex pipe, and begin routing and securing the leads for the O2 sensors. Try and get them as close as possible to the OEM routing locations but in the end your main goal is to keep them away from the heat of the exhaust system.

Re-connect the negative battery cable and you have completed the header installation.

Upon starting my Xterra everything was fine until it threw code P1148 (RIGHT BANK, -B1) CLOSED LOOP CONTROL a mere 5 miles later. After thinking about it and reading through the FSM I followed the following procedures, along with cleaning the engine grounds, and the code went away and all was right with the world.

1. Start engine and warm it up to normal operating temperature.
2. Turn ignition switch OFF.
3. Disconnect mass air flow sensor harness connector, and restart and run engine for at least 5 seconds at idle speed.
4. Stop engine and reconnect mass air flow sensor harness connector.
5. Make sure 1st trip DTC P0100 is displayed.
6. Erase the 1st trip DTC memory. Refer to “HOW TO ERASE EMISSION-RELATED DIAGNOSTIC INFORMATION”, EC-666.
7. Make sure DTC P0000 is displayed.
8. Run engine for at least 10 minutes at idle speed.


Overall I’m very happy with the headers. Throttle response in the mid range is much improved as well as the top end power. Currently I am still running the stock down tubes so there is still a restriction in the exhaust system that will be fixed in the near future with some custom fabricated larger diameter down tubes.

 

Thank you for making this write up. One question, do you recommend using the OEM manifold/header gaskets or the ones that come with the headers?

 

Holy awesome write up batman!

Good job

 

Sweet man!

Rep for you..

 

Awesome, I was on the fence about tackling the headers myself, but it doesnt seem too bad. Thanks for doing all the leg work Racer.
:anbeten-big:

 

Very nice write-up.


+rep

 

Excellent write up!!!!

 

great job!

 

Awesome write up...thinking about getting some new headers down the road...

 

OMG...im wore out just reading this....got to take a break now!

 

Very cool! Rep!

Still looks like more than Id like to take on!

 

good write up

 

Great write up, and you are right, the 2" BL makes a huge difference! You have a ton more room than i did with the DT's.

 

Awesome article here.

 

Sweet now I know the challenges. I'd like to get my headers installed back home before I drive my X to my next duty station.

At least I have a parts list to order and have Dad toss in the box with the headers.

Because I have no one at home to do it for me, I've considered having some of the mechanics back home giving it a run but I know thats gonna run me big in labor.

 

jesus. im going to have a cigarette now. im f'n sweatin too. nice write up. im still on the fence about the DT's but is really has to be done. this writeup will definitely be used.

 

what size are the tubes on those headers they look great noticed any improvements in performance

 

Head tubes are 1.75" and as far as the performance mid range throttle response is better but the majority of the improvement seems to be in top end power. Overall it seems a worthwhile mod for the gains....but unfortunately all my comparisons are skewed. I drove this truck for 10 years stock....then installed 33's and a lift and almost immediately installed the headers. So I really don't have a solid feel for what a lifted truck performs like without headers vs one with them. It's definitely better just how much better is the question.

In my situation I really don't care....I had two cracked manifolds and was not interested in installing two more OEM type manifolds that were going to crack again so headers were the answer.

 

Same boat as you Kelly I think both of mine are cracked and I realized this after the headers.

Its been some time but I'm coming to Yuma for an exercise and then home and I think I'm gonna order the parts (studs and such) while in Yuma and then go home and finally get the headers on my X.

 

Where do the 3 exhaust Flange gaskets for?

 

Where do the 3 exhaust Flange gaskets for?

They are for the Y pipe.

 

so headers to cats get a crushwasher and a 3 bolt gasket each?

 

3 EX Flange Gaskets (2 Bolt)

why a 2 bolt flange gasket if the headers to cats are a three bolt pattern?

 

so headers to cats get a crushwasher and a 3 bolt gasket each?

No I misunderstood you above and edited to fix it ..... sorry. There is no 3 bolt flange gasket it is just a crush washer.

3 EX Flange Gaskets (2 Bolt)

why a 2 bolt flange gasket if the headers to cats are a three bolt pattern?

Because you unbolt the Y pipe to get it out of the way and make room to remove the down tubes. Being a Y pipe it has 3 pipes and connection points all with 2 bolt flanges....so 3 gaskets.

 

got it thanks for editing.