Looks like i ran into another problem.

So i went to the shop the other day. Turns out that the reason why i've been losing so much gas mileage (12mpg) is because i have a leak on my passenger side manifold. The guy told me he cant weld the crack because the manifold is cast iron. He suggested that i buy a new manifold (which happens to be a one piece kit connected with the cat) and replace the cracked manifold.

Its quite costly, anyone have any other suggestions?

That's hardly anything new, almost every Xterra (or any nissan with the VG33) has had or will have a cracked manifold, or several of them. I doubt it has anything to do with your mileage though... never has impacted my mileage. Already had passenger side replaced and driver's side has a 2 inch crack now. I still get 18 - 20 MPG normally. But one thing is true; you have to replace the manifold as there is no way to repair it and have it hold.

Uh, no, he's wrong the one-piece manifold/cat didn't show until 2003 and is much less prone to cracking. The 00-02 manifolds list for $108, part #14004-4S103.
First of all, I'm highly skeptical that a minor manifold crack could affect your mileage. Plenty of people have had the same problem and I've never heard anyone say their mileage was affected.

If you're not inclined to try and have it replaced, you might try this:
http://www.por15.com/PRODUCTS/PUTTYFILLERSSEALERS/FIRESEAL2000/tabid/88/Default.aspx

Brent

Thanks for your reply brent.

.. i figured that it would ruin my gas mileage because a friend of mine actually had the same thing happen to him. His headers were leaking, went to fix it and his gas mileage and throttle response was significantly increased.

Wouldnt that be correct though? A leak in the headers / manifold would create air flow outside of the exhaust. kind of like running open headers. You'd burn more gas because there is no back pressure going back into the engine. Right? Well i could be wrong. But i definately want to fix my gas mileage. If you get 10-12mph, theres definately something wrong with my car.

- Fuel filter changed
- New spark plugs
- Spark plug wires
- Serviced engine recently

What else am i doing wrong?

The only thing i havent fixed or changed is my manifold leak, and im hoping that is the reason why im suffering horrible gas mileage.

Now you're sure that the part number #14004-4S103 for the correct manifold right?

I need one for the passenger side.

If you're positive I will purchase ASAP.

Also you should check a machine shop - you can have cast welded...but it the manifold is only about $100.00 you will be cheaper to buy new.

Yes, that's the updated part number for the passenger side.

As far as I've heard, it should take a hell of a crack/leak (to the point of being intolerably loud) to have any real effect on mileage etc.

Sorry for the noobie questions, but someone stated that the cracked manifold is a common problem. Anyone actually replaced it themselves? or did you all take it to the shop. I hate ripping things appart and finding out that i cant put it back together.

It can be done on your own, but it's not particularly fun. If you don't end up with any broken studs, it's fairly simple. There's just not much room to work. Please read/search previous discussions in problems/annoyances or perhaps backyard mechanic for more info.