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Header Crack v/s MPG

Big_Al

NAXJA Forum User
Location
Gaston Co. NC
I have a small leak where my header is welded together. My exhaust guy said he's only seen a few XJ 4.0's that weren't cracked.

I was wondering if anyone here noticed a gain in MPG after a leak was fixed. I'd like to hear some actual experences.

I know I can spend money on a new header and fight rusty bolts half a day but prefer not to unless there is an increase in MPG.

My 97 4.0 doesn't appear to be running rich but have noticed a drop in MPG lately. TIA.....Al
 
Depends on how big the leak it. The O2 sensor will detect a lean condition and add more fuel. More fuel = less mileage.

As for improvement, what are you getting now? I put a new stock manifold, OEM cat, Cherrybomb Turbo muffler and new O2. My mileage is about 16 hard city, about 22 flying highway.
 
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It'll plug your CAT, you wont be thinking about fuel mileage while paying for that one. Don't ask me how I know this.
 
The leak doesn't seem too bad and sometimes I don't hear it at all.

Well at least they look rusty.:)

I now get about 12.5~14.5 hard city. I have 31's and 4.11 gears (97 4.0 aw4)

Al
 
Im not sure you will notice an INCREASE with a new header, but you will DECREASE with a cracked header. I went from avg 19 to avg 14 with a cracked header. This was a TJ, but Im sure the same effect is seen with an XJ
 
It'll plug your CAT, you wont be thinking about fuel mileage while paying for that one. Don't ask me how I know this.
dont need to ask, been there done that..

the crack will only get worse, and the side affects are a P.I.T.A.

Replace it whenever you get the cash and time.
 
Im not sure you will notice an INCREASE with a new header, but you will DECREASE with a cracked header. I went from avg 19 to avg 14 with a cracked header. This was a TJ, but Im sure the same effect is seen with an XJ

Mine is cracked and is getting bigger every day. I did notice a change in mileage similar to you.
 
My 94 has had a crack for about 4 years. I did not know enough about it till I signed up for NAXJA. I thought it was the exhaust donut I did five times. My 94 is pure stock. I'm happy when I get 17> unloaded on ethanol free gas. I plan on replacing it when I get the bugs worked out of my 96.
 
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