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Unread 03-11-2013, 04:24 PM   #1
Ansleigh
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Getting 6-8 mpg, what could be wrong?

95 XJ, v6 engine 4.0L 120K miles

Ive had my jeep for 4 years, and it usually gets around 14 mpg around town but lately its mileage has been horrible and its doing some other weird things! I'm a college student, so this is the only mode of transportation I have right now, and I would feel a whole lot better if I could get bonnie running well again! Here's the symptoms:

-I'm getting 6-8 mpg
-The air reeks of gas everytime I get out of it after I drive it
-The engine never misfires, but it does idle pretty hard sometimes
-It's taking longer to crank than it used to
-Sometimes I hear a knocking noise after I turn the car off

Side note- I just had an oil change and all my fluids topped off, and it doesnt leak any kind of fluid

Anyone have any ideas about what could be wrong?

Thanks so much!

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Unread 03-11-2013, 05:07 PM   #2
bigbill888
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Did it start doing this immediately after the oil change?
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Unread 03-11-2013, 05:25 PM   #3
xtremzj
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Change your o2 sensors.
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Unread 03-11-2013, 05:53 PM   #4
Ansleigh
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bigbill888- No, it was doing this before also, I thought the oil change might help (plus it was due for one anyways) but no luck

xtremzj- I actually have an O2 sensor that I tried to put on myself when I tuned up the jeep when I first got it, but couldnt get it on. I guess its time to bite the bullet and pay a mechanic to do it for me- Thank you for the advice!
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Unread 03-12-2013, 12:41 AM   #5
Paulio91184
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Yea man, most likely it's your 02 sensors...If they aren't working correctly they make your engine run WAY rich
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Unread 03-12-2013, 11:18 AM   #6
CJ7-Tim
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Are all of your tune-up parts fresh ?

Have you inspected for a cracked exhaust manifold ?

Is the Catalytic Converter working ?

Change your O2 sensors.

.
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Unread 03-13-2013, 09:43 PM   #7
Ansleigh
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CJ7-Tim Thanks for the advice!
-I think the tune up is fairly new- I replaced all of the spark plugs when I had to replace a cracked distributor head 3 years ago (is that new enough considering Ive only put 9000 miles on the car since then?)
-I wanted to see what all yall experts had to say before I jumped to any conclusions, but I was very suspicious of my catalytic converter, especially since a mechanic told me I needed a new one because mine was starting to go bad 2 years ago, but my dad chose to ignore the advice and let it be.
-I have the O2 sensor to put on, and am going to make some more attempts to convince my dad to pay for the catty.
-And I will look into this exhaust manifold- where would I find it on the car? I put in a new exhaust system (muffler and pipes) when I got the car because the muffler was so rusted that I could fit my fist inside the holes in it, and all the pipes were just as bad.
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Unread 03-13-2013, 10:06 PM   #8
x91evo
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the other problem is you have a V6 cherokees came with an I6 lol
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Unread 03-13-2013, 10:34 PM   #9
chris87xj
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mine didn't come with an I6 and has a V6.
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Unread 03-13-2013, 10:42 PM   #10
ss427ci
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Quote:
Originally Posted by Ansleigh
CJ7-Tim Thanks for the advice!
-And I will look into this exhaust manifold- where would I find it on the car? I put in a new exhaust system (muffler and pipes) when I got the car because the muffler was so rusted that I could fit my fist inside the holes in it, and all the pipes were just as bad.
The exhaust manifold is on the drivers side underneath the intake manifold. It will probably be very difficult to spot a crack with it on, but if you listen close you might be able to hear an exhaust leak and that would be a clue.

3 years is a long time, but with that mileage, idk. It'll just depend on the current condition of the parts and plugs, if it looks good, keep it.

X2 on the O2 sensors, they can cause all of your problems.

You might also check for any injectors leaking because of worn or cracked o-rings. With engine running look for any fuel leakage around each injector.
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Unread 03-13-2013, 10:50 PM   #11
ss427ci
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Quote:
Originally Posted by chris87xj
mine didn't come with an I6 and has a V6.
The GM V6 was used from 84-86, but there is no way his 95 is. It is most definitely a 4.0L I6
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Unread 03-13-2013, 10:52 PM   #12
x91evo
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I would say O2 sensor not sensors lol dont need to waste any money.
The only one that would vary engine performance is the 1st one upstream. Not the one after the cat, that one is pretty much useless
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Unread 03-13-2013, 11:06 PM   #13
chris87xj
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Quote:
Originally Posted by ss427ci View Post
The GM V6 was used from 84-86, but there is no way his 95 is. It is most definitely a 4.0L I6
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Unread 03-14-2013, 09:07 AM   #14
habbyguy
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I'll just jump in and add my agreement with the good advice above.

1) Replace the O2 sensor (cheap, and it might well improve your gas mileage even if it's not the root cause of the "big problem". At $4 a gallon, it'll pay for itself in very short order either way.
2) Really, really check for an exhaust leak. The fact the OP had a very rusty exhaust system, and that it's been replaced both point to the possibility of a cracked exhaust manifold (assuming it was rusty and weakened as well, and that the torque of wrenching in that new exhaust system probably cracked it).
3) It's always a very good idea to learn about your vehicles. I see "V6" references on all sorts of vehicles that never had 'em, 2002 and up "Cherokees", etc.
4) Cats seldom actually fail - most times it comes down to an O2 sensor or other issue (cracked manifold)
5) A new tubular header will replace the nasty old iron exhaust manifold for not too much money, and it'll look better, weigh less, and improve performance and efficiency. It's not a huge job to install it, and is something I did based on my MPG dropping from about 24 on the road down to about 18, even though I couldn't really hear an exhaust leak. My manifold was cracked, and the header fixed my mileage issue (and looks cool, to boot).
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Unread 03-14-2013, 01:04 PM   #15
bobbo_xj
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Cat deserves to at least be tested. Sucky mpg, rich exhaust, mechanic previously telling you it is failing. Of course you could have other problems. If you replaced your upstream O2 sensor and spark plugs and have good gasoline, and want to chance it that those items are ok then focus on the cat and failing cat symptoms. Might want to wonder why cat has been going bad though. Caveat: I am no expert, but google helps.
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