Fuel Mileage / Vacuum / Timing Issues Jeep 1993 YJ - JeepForum.com
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post #1 of 7 Old 04-17-2010, 09:07 AM Thread Starter
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Fuel Mileage / Vacuum / Timing Issues Jeep 1993 YJ

I have been fiddling with my first jeep that i just bought a few weeks ago for a while now and have not had much luck. Here is a detailed explanation of what i have been through so far with my current issues at the very bottom next to the *.

1993 Jeep Wrangler YJ 6 cyl. 4.0

Bought a 1993 Jeep Wrangler at a great deal that had new wires, plugs, cap, rotor. Pretty much a complete tune up. My drive from the seller to my house was approx 44 miles so i filled up the Jeep and by the time i got home i was on 1/8 of a tank so almost a full tank. I noticed Carbon coming out of tailpipe heavy like powder.
I then pulled the plugs and started to try to diagnose the problem which i first thought it could be catalytic converter but temperature came out good on that, and also had it checked through emissions and it was good. So i proceeded to the Fuel Pressure Regulator and changed it out and noticed a vacuum line that goes to it had dry rotted rubber boots so changed them out too. This did not fix my problem So i proceeded to the next avenue and cleaned up the Air Intake Control Valve and it was caked up with carbon also and since the idle control valve is right next to it i went ahead and changed it out just for kicks since it was only 12 bucks.
Now i thought this would help it at the least but instead my idle went from running around 1100 rpms up to about 800 rpms with surges up to 1500 rpms.
This obviously didnt do any help. So i went ahead and drove it to hope to clean it up and nothing helped so started to go over with a fine tooth comb.
"Remember this is my first 4 wheel drive and first Jeep" so i get underneath it and notice i have 4 vacuum lines that run off the back of the transmission up to my firewall area that have come in contact with my exhaust and have all melted together (Thank god in a way i could tell which one went to which after i cut and spliced them all together.) So now i crank it up and im running at a smooth idle about 850 rpms and when i drive i feel like i have more torque and the engine is no longer skipping any. So i am assuming these vacuum lines are all intertwined from the transmission up to my fuel line areas and etc. Have not had a chance to drive it on a long distance drive yet.

**Here is my current issue now... When i drove it home from fixing those lines about 5 miles away i can still smell the unburnt gas faintly (not as bad as before) while driving. And when i accelerate going through my gears the check engine light will come on only when my foot is on the pedal. once i release the fuel pedal the light goes out or once i get into 4th to 5th gear the light goes out also. So since that has been going on since the beginning i am assuming i have yet to track down my problem**


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post #2 of 7 Old 04-17-2010, 10:09 AM
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1995 YJ Wrangler 
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If your check engine light is coming on, cycle the ignition three times without starting it, then leave in the on position, and count the light blinking sequence. It is coding, so that should help by first finding out what code it is.
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post #3 of 7 Old 04-17-2010, 10:58 PM Thread Starter
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i tried that and it didnt work. its a 1993 engine and ECM so not sure what im doing wrong there. I took out the o2 censor and cleaned it off (since its only 2 weeks old) and the check engine light is not coming on anymore unless i go into engine overspeed like to high of rpms between swapping gears. think it may be fixed but not sure what or how many miles i should be getting to a tank. right now im getting about 250 mile to a full 15 gallon tank.
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post #4 of 7 Old 04-18-2010, 05:29 AM
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If you have that much carbon in the engine I would use some Seafoam and see how it runs after that. Also if your Jeep is a 4.0L you have a 20 gal. gas tank.
check out this thread for more info on Seafoam.http://www.jeepforum.com/forum/f12/a...angler-957683/


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Originally Posted by Imped View Post
Screw the HOA. More guys just need to start doing man things in the garage.
Originally Posted by aw12345 View Post
Jeeps are like mistresses, they take all your money, but boy what a ride!
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post #5 of 7 Old 04-18-2010, 06:03 AM
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1996 ZJ 
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There is a fuel tank vent line that runs from the fuel tank to the charcoal canister under the washer fluid bottle. The vent line is probably rusted out causing the smell.
iF the CEL goes off there will be no code. I wouldn't worry about it. Just keep checking for codes every now and then.
The OP has a 20 gallon tank if it's a poly tank, but will have to do the 15-20 gal tank mod to get 20 in it.

96 ZJ.
05' Grand Cherokee Limited, 2"OME lift
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post #6 of 7 Old 04-18-2010, 09:07 AM Thread Starter
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Well this is a 1992 model jeep. I left this part out but guess its pertinent now. It was a 4 cyl originally but was swapped over to a 6 cyl just a straight swap everything drivetrain so all the parts are there just has a 4cyl fuel tank with 6 cyl engine.
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post #7 of 7 Old 04-18-2010, 09:22 AM
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1994 YJ Wrangler 
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As Burnerman said, check the charcoal canister. Other than that, if the rims and or the tires have changed from factory this will change the speedo and thus the odometer. With 32's on 15" rims a 4.0l will gets between 12 and 15 miles per gallon depending on where you drive the vehicle. I have a 94' with 32's and 15's and routinely get 14.6 to 15.3 per gallon with an even split between highway and city.

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fuel system , transmission , vacuum lines

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