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Old 09-22-2013, 02:20 PM
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Jeep Grand Cherokee starting issues/mileage drop

I have a 03 Jeep Grand Cherokee Laredo 4.7 4wd. It has about 130k on it and has been great. About 2 months ago I changed the spark plugs as preventative maintenance. Last week as I was driving to Austin, I noticed that the mileage went from almost 21mpg down to 14.8 in the last hour of the trip. Then I noticed the next morning when I was leaving that the engine would wind longer than normal before it starts. During the week it would seem that it didn't want to start correctly, I even held the starter for 15 sec or so, then let off... as soon as I hit the starter again... immediate ignition. I'm thinking that maybe the Throttle positioning sensor is bad, or some form of choke. I am not sure what would change the starting pattern and kill the mileage, but I need to iron this out so my wife can use it!
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Old 09-22-2013, 02:40 PM
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Re: Jeep Grand Cherokee starting issues/mileage drop

Several things could be the cause here. Could be low fuel pressure caused by a faulty fuel filter/pressure regulator. I would start changing this first, cheap item, but sometimes a bit hard to remove the lines. This filter/regulator sits just in front of the rear axle and the fuel line connections get full of road dirt and dust. Spraying then with some kind of lubricant will help during removal. There is a writeup on this in the DIY section of the WJ.
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Old 09-27-2013, 04:59 PM
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Re: Jeep Grand Cherokee starting issues/mileage drop

I just got your reply today. I did replace that booster about 1.5 years ago, and that kinda what I though of. Today it finally decided not to start at all. I changed the IAC sensor, and added some gasoline to see if it was starved for fuel.... it finally started but ran rough, and wanted to stall if you pressed the gas quickly at all. So I'm back to either the fuel filter/booster, or the pump. I cannot hear anything coming from the rear of the jeep when I click the key over right before the starting sequence, so I am thinking that the fuel pump is dead.
That and since the fuel booster is decently new...
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