# Nissan Quest 95 inefficient engine

**URL:** <https://community.cartalk.com/t/nissan-quest-95-inefficient-engine/191789>\
**Category:** Maintenance/Repairs\
**Tags:** nissan, quest\
**Created:** [July 19, 2023, 2:20am UTC](https://community.cartalk.com/t/nissan-quest-95-inefficient-engine/191789 "2023-07-19T02:20:54Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Yusean1792](https://avatars.discourse-cdn.com/v4/letter/y/f05b48/32.png) [@Yusean1792](https://community.cartalk.com/u/Yusean1792)\
**Post date:** [July 19, 2023, 2:20am UTC](https://community.cartalk.com/t/nissan-quest-95-inefficient-engine/191789/1 "2023-07-19T02:20:54Z")

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I have a 1995 Nissan quest with only 80k miles on it. I’m observing black smoke come out of the tail pipe, really poor fuel economy (8 mpg) and a terrible smell. Does anyone know what might be happening and how to diagnose?

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**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\
**Post date:** [July 19, 2023, 2:28am UTC](https://community.cartalk.com/t/nissan-quest-95-inefficient-engine/191789/2 "2023-07-19T02:28:04Z")

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It means the engine is running very rich.

Some of the things that can cause this are a leaking fuel pressure regulator, a thermostat that’s stuck open, or a faulty coolant temperature sensor for the computer

Is the engine light on?

Tester

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**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\
**Post date:** [July 19, 2023, 2:43am UTC](https://community.cartalk.com/t/nissan-quest-95-inefficient-engine/191789/3 "2023-07-19T02:43:15Z")

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A dead oxygen sensor can make an OBD I vehicle run very rich. Unplug the oxygen sensor and see if the engine runs better.

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**Author:** ![oldtimer-11](https://avatars.discourse-cdn.com/v4/letter/o/e79b87/32.png) [@oldtimer-11](https://community.cartalk.com/u/oldtimer-11)\
**Post date:** [July 19, 2023, 2:52am UTC](https://community.cartalk.com/t/nissan-quest-95-inefficient-engine/191789/4 "2023-07-19T02:52:59Z")

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Also a faulty coolant temp sensor or a missing or broken thermostat

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**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\
**Post date:** [July 20, 2023, 11:49pm UTC](https://community.cartalk.com/t/nissan-quest-95-inefficient-engine/191789/5 "2023-07-20T23:49:03Z")

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Other than the tailpipe smoke and odor, does the engine seem to have the normal amount of power? Accelerates as well as before?

Good ideas about the overly rich mixture theory. Another idea, could be internal engine problem, e.g. piston rings. Has engine every been run low on engine oil? Has it ever severely overheated? If the mixture tests ok, suggest to obtain an engine compression test.