fivetears

I am the original owner of a well cared for, showroom stock, 2003 Altima with the QR25DE motor. It has 80,350 miles on the odometer. This is my primary family / trip vehicle. After reading this (and many other) forum, I became deeply concerned about the exhaust manifold PRE-CAT failure rate among owners. I decided bitching about the problem would do nothing, so I took action.

I decided to buy a CAT-LESS racing header. I chose the MEGAN Spec-V header for its quality, material, and price. Although this product is designed for the QR25DE Sentra, It bolted up perfectly to the Altima exhaust system. Let me describe the removal & installation process in detail for any worry warts and naysayer’s out there.

1. Disconnect the battery!

2. Remove the top engine cover by removing 5 Allen head screws.

3. Raise and support the front of the vehicle. Front tires remain in contact with the ground.

4. Remove the plastic pop-rivets from the engine cover in the front passenger side wheel well.

5. Get an assistant. Using a 14mm box wrench, relieve the tension from the serpentine belt, and have the assistant slide a 1/4" diameter bolt (or drill bit) through two aligned pilot holes in the belt tensioner.

6. Remove two 12mm bolts from beneath the relay module box mounting rack, immediately to the left of the alternator pulley. These bolts must be removed to allow the bottom (long) alternator pivot bolt to be removed. You will need a 1/4 drive ratchet to accomplish this.

7. Completely disconnect the red and black alternator wires and its electrical connector. A vehicle harness attachment bracket (10mm bolt) must also be disconnected from the alternator.

8. Remove the alternator from the vehicle (two bolts).

9. Completely disconnect the exhaust pipe from the PRE-CAT header. These two spring pressure bolts are weak ass pieces of shit. They will twist off, bend and or otherwise break off. Do not worry, as this PRE-CAT pile of metal will be heading to your trash can. I had to use large vice-grips to grab a hold of them and bend / snap them off.

10. After you've cooled off, there is one more bolt to remove from the PRE-CAT header. There is a bracket that secures the header to the motor block. Disconnect the header from this bracket. If you choose to remove the bracket, DO NOT DISCARD IT!

11. Carefully disconnect both O2 sensor electrical connectors. You must firmly depress the locking tab on each connector, before pulling it apart to disengage.
DO NOT PRY OR FORCE THESE TWO CONNECTORS APART! DO NOT TWIST OR PULL ON THE WIRING ON THESE TWO ELECTRICAL CONNECTORS!

12. Manually un-clip each O2 sensor from the existing pinch brackets.

13. Remove all heat shielding from the front side of the PRE-CAT header assembly. Use care when guiding the lower heat shield over and through the lower Secondary O2 sensor. Some rusted 10mm bolts may break off during this process. They will become trash material anyway.

14. Carefully remove both O2 sensors from the PRE-CAT header.
DO NOT SPINDLE, TWIST OR OTHERWISE GAFF UP THESE WIRES WHILE REMOVING THE SENSORS! O2 SENSORS ARE DELICATE INSTRUMENTS.

15. Remove all self-locking nuts from the PRE-CAT header assembly.
DO NOT DISCARD THEM!

16. Discard the PRE-CAT header, gasket, heat shields and donut gasket. Yes I found the catalyst containment screen intact, but with two small holes. I then barely touched the screen with a flat tip screwdriver (through the O2 sensor hole) and it broke through; EASILY BROKE THROUGH!

INSTALLATION is in the reverse order of the removal with the following added points:

1. Torque all hardware to manufacturer specification.

2. Use all new gaskets and hardware supplied with your new MEGAN Racing header.

3. Use anti-seize compound sparingly to the threads of all hardware securing the stainless steel header.

4. Modify the AUTOZONE HELP P/N 42009 (package of two) as specified throughout this message board. You drill out one spark plug non-fouler using a 1/2" drill, while retaining the second non-fouler to be installed in the lowest O2 sensor position on the new MEGAN Racing header first. The correct order is spark plug non-fouler, modified spark plug non-fouler, then second (lowest O2 sensor. Use anti-seize compound sparingly to the threads of these components.

5. Both O2 sensor electrical connectors do not just slide and clip back together. You must firmly depress the locking tab on each connector, before pushing it back together.
DO NOT FORCE THEM OR YOU MAY DAMAGE THEM.

6. The O2 wires will require some very minor repositioning. REMEMBER: DO NOT STRETCH, PULL OR OTHERWISE FORCE THEM TO THEIR NEW LOCATION. A couple ty-straps will be useful.

7. The MEGAN Racing header does not come equipped with a mount bracket for where the header collector flange is mounted to the motor block bracket. SEE REMOVAL STEP 10. Using 2" mild steel angle bracket, a 1/2" drill, and standard metal working tools, I manufactured a new piece. I chose to weld it to the factory bracket retained in step 10. I could have used hardware, but welding was easier. If you do not manufacture / reinstall a bracket in this position, you will experience exhaust manifold vibration and buzzing. Cracks in your new header will surely follow. Don't be stupid; use your head and make a new bracket.

THAT'S IT!

I am very pleased with the installation. Since this is my family / trip car, I have no intention of any further modification to the exhaust system. This header is impressively quiet. There is only a slight growl under the hood during acceleration while going through the gears, and intentionally passing other vehicles. This header is very peaceful. Noticeable performance gain? Nope. Gas mileage increase / decrease? Nope. It's the same 28 MPG with A/C on in San Antonio, Texas. Threw the pretty MEGAN Racing decals in the trash, so as not to attract attention and advertise on the street.

Do yourself a big financial favor, and give yourself vehicular peace of mind; AX YOUR ALTIMA QR25DE PRE-CAT NOW!

What? The CEL light? The Check Engine Light? WHAT STINKIN' CHECK ENGINE LIGHT? Follow the instructions ALL OVER THIS GREAT WEB SITE, and in my INSTALLATION Step 4.

Stop it already!!!

FIX YOUR DAMN QR25DE PRE-CAT ALTIMA!

I DID!

Brian.

 

roadkill2_0

hi im the owner of a 2004 2.5S with 67000 miles on it....you think ill have this "pre-cat" problem? If so, i want to take care of it early....thank you

fivetears

Judging from what many have posted all ready... I wouldn't gamble on it. That's why I posted this procedure. ... And STILL No CEL. Protect yourself and your ride. Good luck.
Brian

civiceatr87

I have heard of this problem too but it you goto www.dmv.org/recalls there is no such article. So if it is truly a serious issue, i think Nissan would send out a recall on it. But it is still in your best intrest to do as much research as you can on it. I havnt come up with much yet myself.

civiceatr87

CORRECTION: AUTO RECALLS - Tire & Child Safety Recalls - Vehicle Recall Search - DMV.ORG

That is the right URL

 

fivetears

Read carefully here;
There's enough good information and enough CRAP all over the web on this topic. I consider myself LUCKY discovering the importance of this issue by accident, while web reseaching a HID modification on my '03 Altima here on this MB. Damn sure enough... the screen on my PRE-CAT was deteriorated by heat and 80,350 miles of normal driving. Punctured easily.

Do as you may my fellow QR25DE Altima readers! Take my advice above... or read'em and weep when it happens to you.

To any and all naysayers... you'd make great Nissan vehicle maintenance managers.

That's my last trip to the top of the soapbox, on this thread. PM me if you need any technical help with the process.

OUT!

cebesius

I tried to follow fivetears' instructions, but I had some trouble understanding what he meant in the install step 4. We went back and forth via email, and I finally figured out what he meant. Here is a diagram that shows where each O2 sensor mounts to the header, and where to put the spark plug non-foulers.

fivetears

Nice job Carlton. You nailed it.