Evap leak codes and bad gas mileage - JeepForum.com
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post #1 of 18 Old 07-09-2019, 09:29 AM Thread Starter
Figgy
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Evap leak codes and bad gas mileage

Hey where do I start ? Jeep is a 04 LJ Iím the original owner . I havenít driven it much in the last 6 years . Where do I start .

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post #2 of 18 Old 07-09-2019, 10:21 AM
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how bad is your gas mileage?
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post #3 of 18 Old 07-09-2019, 11:45 AM Thread Starter
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10 mpg or less
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post #4 of 18 Old 07-09-2019, 12:42 PM
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For the evap codes, start by checking for a leaking fuel cap seal and check your evap lines and connections at the fuel tank, charcoal cannister/LDP, and intake manifold.

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post #5 of 18 Old 07-12-2019, 09:11 PM Thread Starter
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I think I found my issue and itís expensive for just a pice of plastic !
What does this thing do ?
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FE618162-827B-42B1-B660-BFFD36AF6737.jpg   26298CFE-D87C-4D39-B4C6-679D317086EE.jpg   7BC681E4-E6BE-4D6E-BEFB-5B16820892D1.jpg  
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post #6 of 18 Old 07-12-2019, 09:13 PM Thread Starter
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Flow control valve ,can that broken line cause issues when I fill up the tank? Or loose gasoline because venting into the atmosphere.

Last edited by Figgy; 07-12-2019 at 09:34 PM.
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post #7 of 18 Old 07-17-2019, 02:27 PM
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A couple days after reading your post I got a code again PO456 Evap system small leak. I had this code before so thatís where I started. The hose going down from the front Evap valve to the frame is connected with a rubber hose. It cracked on the lower end where it connected to the metal tube at the bump of the metal tube. The first time I just trimmed the rubber hose and that solved the leak. This time the hose was to short and fairly hard. This connection is on the left side at the front of the skid plate. You can see the bump in the new hose installed from the metal tube and the cracks on the old hose.
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post #8 of 18 Old 07-17-2019, 02:54 PM
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@Figgy
Sorry, missed your question earlier. The flow management valve is part of your evaporative emissions system. It meters the vapour to the EVAP cannister during fueling and normal engine operation, and serves as a liquid separator to keep fuel out of the cannister. You need it to have your evap system work correctly.

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post #9 of 18 Old 07-18-2019, 06:22 PM Thread Starter
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Thank you for the info
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post #10 of 18 Old 07-18-2019, 06:58 PM
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Evap codes and mileage are most likely not related unless there is maybe a very major vacuum leak associated with it. And I mean major. If you have not driven it much in 6 years you may have varnish issues and gum in your fuel system and even traces or amounts of very degraded fuel.

Give it lots of fresh fuel. Use a fuel system cleaner that contains techron. It can be branded by OEMs or even by chevron. Pretty good stuff. It may or may not help you. Old nasty fuel is evil though. It gums stuff up. If it turned to varnish there may be a lot of work involved like pulling fuel tank to clean, etc.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #11 of 18 Old 07-18-2019, 08:48 PM Thread Starter
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I actually use rec fuel for about half my fuel usage in the the last 5 years . The engine runs great no hesitation no miss fires . I have a major evap leak . I believe Iím just having some fuel evaporating .
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post #12 of 18 Old 07-19-2019, 07:23 PM
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I will post one paranoid thing here. DO NOT get tempted to test your evap system with shop or compressed air.

Here is why. Fuel tanks naturally displace ambient air or oxygen in plain terms by the fuel vapors always pushing air outward. The vapors pushing out do not allow for outside air, thus oxygen in high enough concentrations to enter the tank. Fuel pumps and senders inside of tanks are electrical and make sparks. Combustion needs three things. Fuel, Oxygen and an ignition or spark. A normal fuel tank lacks the oxygen, thus why normal fuel pump operation does not make cars explode. I once saw a video of a fuel pump inside a tank that showed how much sparking the fuel pump brushes produced. It made my butt pucker.

There are a lot of DIY evap testing methods on youtube and the net in general. Many are dangerous. Be careful. This is the reason that professional EVAP machines use a tank of nitrogen. Other inert gases can work also.

Not sure if you were going to go in this direction, but don't.

If you really have a HUGE evap leak, many of them can be found visually.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #13 of 18 Old 07-20-2019, 11:23 AM Thread Starter
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Quote:
Originally Posted by Boojo35 View Post
I will post one paranoid thing here. DO NOT get tempted to test your evap system with shop or compressed air.

Here is why. Fuel tanks naturally displace ambient air or oxygen in plain terms by the fuel vapors always pushing air outward. The vapors pushing out do not allow for outside air, thus oxygen in high enough concentrations to enter the tank. Fuel pumps and senders inside of tanks are electrical and make sparks. Combustion needs three things. Fuel, Oxygen and an ignition or spark. A normal fuel tank lacks the oxygen, thus why normal fuel pump operation does not make cars explode. I once saw a video of a fuel pump inside a tank that showed how much sparking the fuel pump brushes produced. It made my butt pucker.

There are a lot of DIY evap testing methods on youtube and the net in general. Many are dangerous. Be careful. This is the reason that professional EVAP machines use a tank of nitrogen. Other inert gases can work also.

Not sure if you were going to go in this direction, but don't.



If you really have a HUGE evap leak, many of them can be found visually.

Oh I wasnít going to do that. I live in Florida I donít have emission testing I just hate the CEL on the dash . I found my leak Itís in the pic up there .
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post #14 of 18 Old 07-22-2019, 06:54 PM
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After I replaced the damaged hose it took three days for the engine light to go out on itís own.
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post #15 of 18 Old 07-22-2019, 08:42 PM Thread Starter
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Iím still waiting for the new hoses .
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