could someone do a writeup for me? - JeepForum.com

 
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post #1 of 11 Old 09-23-2010, 01:48 PM Thread Starter
wj_jeep92
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could someone do a writeup for me?

hey guys Im getting about ~12mpg on my stock rig. so ive decided to change my fuel filter and see if that helps it out any. so if someone could do a writeup on how to change the external filter (from my understanding there are two) i would appreciate it. i looked on wjjeeps and i couldnt understand what they were getting at.


1998 ZJ 5.9L
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post #2 of 11 Old 09-23-2010, 01:53 PM
WiCkeDuDe
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The one in the tank isn't meant to be replaced. The replaceable filter/regulator is held on by 2 bolts, just above the rear axle and the fuel line simply press and pull off.
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post #3 of 11 Old 09-23-2010, 02:20 PM
volvite
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I might be able to. I'm currently putting a lift on my jeep and since i need to replace mine anyway I'll see what I can do unless someone else has already done it.
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post #4 of 11 Old 09-23-2010, 03:02 PM
jdrogers
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Quote:
Originally Posted by wj_jeep92 View Post
hey guys Im getting about ~12mpg on my stock rig. so ive decided to change my fuel filter and see if that helps it out any...
I don't understand something here. How can a plugged fuel filter cause poor mileage?

2002 WJ Limited, Stone White, 4.7L H.O., Quadra Drive
OME Springs, MX6 Shocks, BFG 265/70R17 All-Terrain, Level 8 Tracker Wheels
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post #5 of 11 Old 09-23-2010, 03:43 PM Thread Starter
wj_jeep92
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Quote:
Originally Posted by volvite View Post
I might be able to. I'm currently putting a lift on my jeep and since i need to replace mine anyway I'll see what I can do unless someone else has already done it.
i havent seen one done for a wj yet so i encourage you to do it

1998 ZJ 5.9L
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post #6 of 11 Old 09-23-2010, 03:45 PM Thread Starter
wj_jeep92
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Quote:
Originally Posted by jdrogers View Post
I don't understand something here. How can a plugged fuel filter cause poor mileage?
no idea. if i had to make a guess i would say it clogs up a little bit and restricts fuel flow, which would make it feel less powerful and require more skinny pedal which feeds more fuel into it. if that bs i just spewed it right, that'll be 10.00

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post #7 of 11 Old 09-23-2010, 04:27 PM
WiCkeDuDe
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The filter assembly is also the pressure regulator on the WJs. Thats usually what goes bad, not the actual filter.
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post #8 of 11 Old 09-23-2010, 04:35 PM
jdrogers
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Quote:
Originally Posted by wj_jeep92 View Post
no idea. if i had to make a guess i would say it clogs up a little bit and restricts fuel flow, which would make it feel less powerful and require more skinny pedal which feeds more fuel into it. if that bs i just spewed it right, that'll be 10.00
I don't think that line of reasoning applies to a fuel injected engine. The computer commands the injectors to provide the proper amount of fuel based on the air flow through the throttle body. So restricted fuel flow would only come into play at wide open throttle and only if there was not enough fuel available. I'm pretty sure this is not coming into play during normal driving. And I would think this situation would result in misfires (which would show up as P03XX codes).

A more likely reason for poor fuel mileage could be a bad TPS which is telling the computer that more air is passing through the throttle body than actually is. The computer would then command too much fuel to be injected. I'm not sure the computer can detect this situation?

But hey, I liked your explaination. Maybe more beer will resolve the issue!


2002 WJ Limited, Stone White, 4.7L H.O., Quadra Drive
OME Springs, MX6 Shocks, BFG 265/70R17 All-Terrain, Level 8 Tracker Wheels
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post #9 of 11 Old 09-24-2010, 09:46 AM
dlwilson42
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There is some discussion of this issue in this thread: http://www.jeepforum.com/forum/f310/hello-jf-bad-mileage-question-1103937

I think that if the fuel pressure regulator is too high, then too much fuel will pass through the injectors when the computer opens them. I just bought a $16 fuel pressure gauge at Harbor Freight, and this weekend I will check my fuel pressure, before replacing the fuel filter/regulator. First I need to go through the manual and see what the pressure should be.

2004 Grand Cherokee Freedom Edition 4.7 HO, bought 3/17/10. w/ 97K miles. stock, except for Edelbrock Performer IAS shocks and AddCo rear swaybar.
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post #10 of 11 Old 09-24-2010, 11:23 AM
jdrogers
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Quote:
Originally Posted by dlwilson42 View Post
There is some discussion of this issue in this thread: http://www.jeepforum.com/forum/f310/hello-jf-bad-mileage-question-1103937

I think that if the fuel pressure regulator is too high, then too much fuel will pass through the injectors when the computer opens them. I just bought a $16 fuel pressure gauge at Harbor Freight, and this weekend I will check my fuel pressure, before replacing the fuel filter/regulator. First I need to go through the manual and see what the pressure should be.
Be sure to post your results here! Thanks.

2002 WJ Limited, Stone White, 4.7L H.O., Quadra Drive
OME Springs, MX6 Shocks, BFG 265/70R17 All-Terrain, Level 8 Tracker Wheels
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post #11 of 11 Old 09-25-2010, 01:52 PM
dlwilson42
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I updated the other thread, but basically I saw a steady 50 psi at the rail, which is just right. No need to replace the filter.

2004 Grand Cherokee Freedom Edition 4.7 HO, bought 3/17/10. w/ 97K miles. stock, except for Edelbrock Performer IAS shocks and AddCo rear swaybar.
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