1997 Jeep Wrangler Mileage and the exhaust manifold

Tiny
REDDOG7854
  • MEMBER
  • 1997 JEEP WRANGLER
  • 6 CYL
  • 4WD
  • MANUAL
  • 85,000 MILES
Recently my exhaust manifold decided to crack in 3 places. Parts are on the way to replace. Previous to the cracks my gas mileage was standard for a 4.0L Jeep but now it has dropped to 10-12mpg. Is it possible for a cracked manifold to affect the mileage that much or should I be looking for a different culprit?
Sunday, January 11th, 2009 AT 9:13 PM

1 Reply

Tiny
BLUELIGHTNIN6
  • MECHANIC
  • 16,542 POSTS
The cracks will allow air to enter the manifold and this air will make the oxygen sensor(s) say engine is lean. Then the ECU will force very rich fuel injections. This will cause very poor gas mileage and eventually will harm the catalytic converter(s).

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Sunday, January 11th, 2009 AT 9:33 PM

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