Would having a small crack in the exhaust manifold be killing my mpg? Im getting about 10-12mpg, I didnt notice my gas going down so fast until i started to notice the tick sound, and got new tires. (tires are just 235 75 15 though)

Also when replacing the headers the 01 XJ has two parts, the front and rear, then its the pre cat. Is it the same methods as replacing the 1 piece headers with no pre cat? Are any bolts impossible to get to with the pre-cat there?

 

Yes a cracked header will effect gas mileage how much I dont know,when replaceing any bolts that are not on the head use a torch set and burn them off and replace with new hardware.

 

it will effect it alot trust me, i went from where you are 10-13 up to about 18-21, but i also did full exhaust with aftermarket header, and full tune up, next is 703 injectors

 

It will affect it because it gives a false reading to the O2 sensor

 

what aftermarket brand did you go with? I was just thinking of getting the APN header since its cheapest, but apparently good.


the 01 xj has the pre cat, would it be better if I eliminated that and did a whole new exhaust system headers and back? I know the pre cats have 2 o2 sensors in them though wouldnt I need to keep thep re cat then? , but when i was checking things out the pre cats looked pretty beat up, but from what i seen they cost 300 dollars.

 

it depends where you live, i know we cant talk about removing or gutting cats on here but you are going to keep the post cat so i dont see harm it it, Anyway you could get rid of the pre cat, and then header and have a o2 sensor bung welded in, unless you can do it yourself, I have a pacesetter header, alot of ppl dont like them because they use a 3-3-2-1 sorta deal, but i like it, sounds nice with my flowmaster