Big crack in exaust manifold, how does it effect MPG?

My 96 has a RE 5.5" kit with 33's and stock gears its manual and as for the exaust well, I have a nasty crack in the manifold and then i have no cat with no rear O2 sensor (its disconected and the harnes is coiled up hanging on the TC) How much better will my MPG get if i replace these things and what would be the most cost effective? Im broke.

by replacing the cat you could avoid paying a huge fine, which would make you broker

depending on where you live.


your probably getting like 5mpg with all those problems.

To save money weld the crack in the manifold. I`ve welded several with my wire welder.Rock Auto has the best price on o2 sensors. Having the sensor will improve mpg. The universal cats are under 100.00 in my area.

The rear o2 sensor doesn't affect the fuel mixture, it only checks the efficiency of the cat. I assume you have a check engine light on due to the sensor being MIA though.

Is the manifold plain steel? I have about a 2-1/2 inch crack in mine and was looking at replacing it. But if it's plain steel, I can MIG weld it. I have the equipment and skill to do that. If it's a special steel, I might not want to try it.

so i shouldnt bother replacing the cat, im not worried about getting a ticket that wont happen but if it wont help my MPG the F it, I have the original manifold so im going to take it out and have a buddy weld it. and ya about 6mpg with 80% highway

kenny schmitt said:

My 96 has a RE 5.5" kit with 33's and stock gears its manual and as for the exaust well, I have a nasty crack in the manifold and then i have no cat with no rear O2 sensor (its disconected and the harnes is coiled up hanging on the TC) How much better will my MPG get if i replace these things and what would be the most cost effective? Im broke.

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Dude! The most cost effective option is to sell the jeep! LOL

Welding the Manifold leak can have a huge improvement on your mileage, the leak fools the front O2 sensor and makes the PCM run the engine real rich even in closed loop.

Emissions + huge fines? My God where do you folks live? Here in Gods' country (Western Oregon) we don't have emission standards or inspections or safety checks. Hell it even appears that speed limits may be veiwed as useless. No sales tax! Not enough money budgeted to hire State troopers.
Mild winters warm summers, green all year. Wheel all the time. Want snow? Just an hour away going east from the west side if you like that kinda thing?! Yuck, I hate the cold.
Oops, got carried away....we drink in the early afternoon here right after the coffee hour.
I'll leave now....thanks
:greensmok