10.5 a gallon

Asked by Jul 15, 2011 at 03:48 AM about the 1994 Jeep Grand Cherokee Limited 4WD

Question type: Maintenance & Repair

Hey Fellas.. Have a 94 318 with 120 k. A few years ago I was avg. 13.5 city and 18 Highway. Fuel mileage just continued to go to hell and it sometimes has a huge miss, runs really rough for a few mins. when I start hot with A/C on. I do have some rattling noise from cat. ( Insides broken loose, plugged ? )  Did a complete tune also injection clean and new 02 sensor on top of intake. Ran a little better for a week, then back to the same old crap with noticeably rough idle.   I'm thinking maybe multiple problems, any one with me on these scenarios ?

2 Answers

55

i had almost the same problem with my 95 JGC. I had to change the fuel pump to fix it. it might be the same with yours. I have the 4.0 I6 and i get between 18 and 22 mpg now. i was getting alot less before i changed the fuel pump. you can try doing that, it might help.

120

Vacuum leak somewhere possibly causes rough idle and other trouble. I too have an 04 I6. MPG actually can increase with the right vacuum leak meaning I have experimented with allowing controlled vacuum leaks. Any in the purge type systems cause trouble. But I have improved mpg to as high as 36 highway by putting a T in the vacuum line that goes to the interior air flow control and putting a little air filter on it.

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