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Unread 01-04-2014, 08:39 AM   #1
DiveFlyFun
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2000 4.0 runs rough at 45 mph

When I leave home there is a six mile stretch. For some reason my Cherokee runs rough and sometime backfires if I punch it at 45 mpg. Its runs great at all the other speeds/times. Any ideas why I have this problem? Thanks

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Unread 01-04-2014, 09:26 AM   #2
CJ7-Tim
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Test the O2 Sensor and the Coolant Temperature Sensor. Inspect their wire plugs and wire harnesses for damaged and/or chafed insulation.
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Unread 01-04-2014, 10:17 AM   #3
DiveFlyFun
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O2 sensors already replace...will check the coolant sensor. Thanks
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Unread 01-04-2014, 04:22 PM   #4
tjwalker
It's the crank sensor!
 
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*Assuming that you haven't seen a check engine light? If so, must retrieve codes for guidance.

*Good idea to check the coolant temperature sensor

*I would verify fuel pressure with a stone cold engine and see if it is in spec., which is 49 psi, plus or minus 5 psi. I have seen a fuel pump be marginal at initial start up after which pressure stabilizes after engine has run a bit.....

Good luck and keep us updated!
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Unread 01-23-2014, 10:39 AM   #5
DiveFlyFun
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Replaced the coolant temperature sensor and the problem is gone. I would have never thought of that sensor...thank you very much for your help!!!
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Unread 01-23-2014, 11:06 AM   #6
CJ7-Tim
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Glad it was a simple fix.
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