2001 Jeep Cherokee Jeep idles rough and gas mileage down to

Tiny
JEEPER2001
  • MEMBER
  • 2001 JEEP CHEROKEE
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 98,000 MILES
My jeep runs good until warm and is shut off. Upon restart it starts idling rough. My gas mileage went from 20 mpg to 15 mpg. It had a recent tune up and the check engine light said cyl 3 misfire, so I changed the injector, didnt fix the issue. Ever since the gas mileage went down the rpm's are 300 higher at 55 miles an hour. Any thoughts would be appreciated, o2 sensors havent been replaced and catalytic converter is stock. Thanks
Wednesday, February 25th, 2009 AT 5:33 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Has the #3 misfire been repaired? Have you checked to make sure the plug wire isn't shorting against the engine? As far as the catylatic converter, listen to make sure you don't hear a hissing coming from the exhaust or ratteling that would indicate a converter problem. Also, a bad O2 sensor can cause the poor MPG. You may want to have that checked too. Has the ck engine light come back on?

Joe
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Thursday, February 26th, 2009 AT 6:33 PM
Tiny
JEEPER2001
  • MEMBER
  • 2 POSTS
The check engine light went off itself and hasnt been back on, prior to fixing the number three injector. The jeep doesnt have spark plug wires is has a spark rail where the boots are directly hooked to the plugs. The o2 sensors havent been replaced yet and the jeep has 98000 miles. There are 3 O2 sensors. As far as the converter, the exhaust system has a wierd rattle when its first started which vibrates the floor board under my foot, it almost feels like its restricted. I have access to a scanner which will show me the ranges that the sensors are in, if I start the engine and check the O2 sensor ranges they should flucuate if I rev it up, is that correct? Thanks

Tony
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Saturday, February 28th, 2009 AT 9:33 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Yes, the O2 sensors will. I wonder if the insides of the cat are loose and blocking the exhaust. Also, are the boots on the spark rail good?
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Saturday, February 28th, 2009 AT 1:16 PM

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