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Old 09-01-2008, 07:32 PM   #1
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Mileage catastrophes. Any ideas?

Here is my sob story. I have a 92 yj, 180 thousand on the engine. I bought it from a kid I think its pretty beat. I get more than horrible gas mileage, to the tune of $40 for about 200 miles. It's got a three and a half inch lift and 31's. I am getting a little blow back of oil into the air filter, and the mechanic I use says that I need a ring job or better yet another engine. It's not blowin' any smoke, and I am confused. Does any body else think that my mechanic is trying to hose me for the engine replacement? Would a tune up do the trick or is my mechanic right? any ideas? I really hate the eight hundred a month gas bill I have, but I love my truck. Help.

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Old 09-01-2008, 09:22 PM   #2
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6 Cyl? Doesn't sound too far off.......

Replace O2 Sensor, especially if you have been getting Check Engine light.

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Old 09-01-2008, 09:25 PM   #3
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make sure the pcv valve isn't clogged that can cause the oil to blow out into the air filter.
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Old 09-01-2008, 09:34 PM   #4
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200 miles a tank for $40 is about right. Not sure what gas is right now, deployed, but @ $3.50/gal for 15gallons to fill up = $52, And I only get around 220 miles a tank along with most people on here, so you are right in the ballpark. As for the oil, my air box has always had some oil/sticky lube which is just from the air filter, i use a K&N which I clean and recharge every oill change or after a hard dusty off road adventure. Not questioning your judgement on spitting back oil, but are you sure its engine oil and not air filter oil? Either way Id do a full intensive tune-up if it hasnt been done recently and get a second opinion on the engine.
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Old 09-01-2008, 11:02 PM   #5
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Quote:
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make sure the pcv valve isn't clogged that can cause the oil to blow out into the air filter.
It doesn't have one.....PCV valve. At least a 94 doesn't.
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Old 09-02-2008, 07:14 PM   #6
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could have plugged vacuum lines. I had an 89 that blew oil like that and it ended up having some pugged vac lines. The rigid metal ones mounted to the engine.
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Old 09-02-2008, 08:25 PM   #7
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so what if there is alot of blow by and your piston rings are fried, just get used to using a quart of oil every week!!!
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Old 09-03-2008, 09:20 AM   #8
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Quote:
Originally Posted by porkchop71 View Post
Here is my sob story. I have a 92 yj, 180 thousand on the engine. I bought it from a kid I think its pretty beat. I get more than horrible gas mileage, to the tune of $40 for about 200 miles. It's got a three and a half inch lift and 31's. I am getting a little blow back of oil into the air filter, and the mechanic I use says that I need a ring job or better yet another engine. It's not blowin' any smoke, and I am confused. Does any body else think that my mechanic is trying to hose me for the engine replacement? Would a tune up do the trick or is my mechanic right? any ideas? I really hate the eight hundred a month gas bill I have, but I love my truck. Help.
Why in the hell do you use a jeep for a daily driver? If you are looking for fuel economy...get a car with a 4 cylinder.
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Old 09-06-2008, 08:08 AM   #9
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fuel mileage

I would first do a compression check,refer the manual for directions. this will rule out the obvious. My 94' with a 2.5 4 cyl., 33" tires, 4.10 gears, I get around 16 miles per gallon. Before I installed electric fan, and a home made cold air kit with a K&N air filter I was getting about 14 mile's per gallon. I am pleased with it,what else do you want? buy a prius. My 2007 GMC 2500 with 6.6 duramax turbo diesel gets 16 to 17 miles per gallon around town and as high as 22 miles per gallon on the Highway. But the the best part of that is IT HAS OVER 600 FOOT POUNDS OF TORQUE, and 345 Horse's.
I agree buy, a 4 cylinder car to run every day not a jeep for economy.
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Old 09-06-2008, 09:00 AM   #10
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It doesn't have one.....PCV valve. At least a 94 doesn't.
I know tj's dont i thought yj's did matbe only early ones.
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Old 09-06-2008, 09:14 AM   #11
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Quote:
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I know tj's dont i thought yj's did matbe only early ones.
There should be a metal tube coming off the valve cover, thats all it has. Pull it off and clean it out with carb cleaner, my bet is it's full of crude.

My YJ with 33s gets around 14/15 mpg. Thats with a K&N, TB spacer, header and a Flowmaster.
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Old 09-21-2008, 11:27 AM   #12
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Also make sure your exhaust isn't being restricted. Slow exhaust can cause problems as well. I'm planning on getting a Ractive #7101 Metal core cat. I know it's marketed more for tuners but its the same as the Random Technologies unit, if you look at it, but at half the price. But you'll have to put a new port for you O2 sensor.
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Old 09-22-2008, 07:51 AM   #13
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I had the same problem in my jeep about two weeks ago. The back blow comes from the air flow being blocked out of the engine. Meaning that your exhaust system has a block somewhere in it. For me, it was my CAT, which caved in and caused a few pieces to shoot back in to my muffler. I had to replace both but now, its running fine.

Hope this helps.
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Old 09-23-2008, 11:46 AM   #14
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Correction..... I got the brand name mixed with something else, its Vibrant that makes the metal core cat part # 7101

Vibrant Performance::.

Sorry about the mix up
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Old 10-12-2008, 07:34 PM   #15
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Re blow by

I got the same problem but I got a 2.5L (4 banger) and it's a 90 but recently was told either something is clogged or it will need rings. I'm just as lost as you and it's also pushing the oil out the dipstick. and your gas bill won't get better I got 33in. tires 3in. lift with 456 gears and yes its a daily driver I get 238 miles to the tank full but I swapped in a 20 gallon tank.let me know what you do to fix problem...
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Old 12-11-2008, 10:12 PM   #16
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I have a 94 yj that is doing the same thing . I check the oil everyday and its fine . It may just be some blow back . I have high oil pressure when I first start it up . But it drops off a little after I drive it a while . I get 350 miles per tank of gas and my jeep has over 160 thousand miles on it . I drive it every day . If you have low oil pressure you may need a ring job or you could have a weak oil pump . If you have high oil pressure something is clogged . With the year of your jeep I think something may be clogged . If you got it from a kid I know something is clogged....Good Luck....
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Old 12-12-2008, 12:21 AM   #17
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Remove the oil cap while idling put your hand over the fill if you feel pressure blowing at your hand you likely have some blow by. Check PCV valve and all vacuum lines especially the one going to the pcv valve. Good strong vacuum required on that hose.
Good Luck
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Old 12-12-2008, 12:33 AM   #18
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with that many miles i agree its probably blow by.. I have the same thing but its not bad only a quarter sized spot on my filter every 3000 miles. 135,000 on the 2.5L

Just an educated guess
The compressions rings must be worn and the oil ring must be ok on the piston. This would allow pressure past the compression rings into the crankcase but the oil rings are still keeping the oil out of the cylinders.
so no burning oil but crankcase pressure
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Old 01-09-2009, 02:13 PM   #19
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wow i was unaware of this i guess im gonna have to check mine out. i was thinking of changing the gear ratio to get better fuel mileage but i just dont know what to change to
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Old 01-09-2009, 03:27 PM   #20
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gas at 1.50 i put 25 in and get 200 miles. perfect for a 6cyl. and im pushing 35"s on a 5 inch lift.
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Old 01-11-2009, 09:40 PM   #21
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Try this, compression test all cylinders then put in a tablespoon of oil in your spark plug hole, if the compression shoots up. The ring/cylinder is worn. I would remove the valve cover and look for smegma under it. Smegma as I call it, is oil deposist built up by not having normal oil changes. The valve train is fed oil which in turn drains to the oil pan through holes. I have seen these holes clogg from smegma. Your Jeep like my 92 has a closed pvc system. this keeps the engine under a vacuum and the oil can be pulled into the air filter via the 1/2 pipe at the rear of your valve cover if the oil can not drain. Also remove your oil fill and feel for a vacuum or pressure. I will check mine tomorrow and let you know what it is doing. I have 95k on mine.

Just my 2 cents.
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Old 01-12-2009, 08:21 AM   #22
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Crankcase venting

The crankcases all have positive pressure, its part of modern emission control. For some reason jeeps seem to be prone to blowing oil even with good rings, my logic for believing this are the many threads related to oil in the breather, coming out of dipstick etc. My mouse was blowing oil as well and the rings check out fine. There is no PCV valve (as in old system that used a vacumn actuated venting valve) but rather a PCV fitting, the elbow sticking out of the valve cover and connected via a hose to the breather. This is the air inlet, it provides filtered air into the crankcase. The air is removed out of the crankcase via a small orifice fitting on the side of the valve cover, on the manifold side (opposite side from distributor and plugs). This small fitting is connected via a vacumn hose to a fitting underneath the throttle body on the intake manifold. The purpose of this is to remove gases from the crankcase via manifold vacumn and combust them with fuel to prevent them from entering the atmosphere. The engineers at detroit call this a CCV system. (Crank Case Venting) Take out the fitting from the valvecover and clean with solvent (spray carb cleaner works good). Make sure it is completely clear of obstruction. Put a little loctite on it and reinstall. Attach a piece of new fuel line to the fitting and route to the manifold connection. Check it frequently to make sure it hasnt collapsed, come loose, or leaks. This is all you can to do to prevent crankscase pressure. Make sure the dipstick is firmly seated and dont overfill with oil.

oh, and never ever run the engine even at idle with the oil cap off, it makes a huge mess under the hood.


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